November 2004

MIC280

Micrel

MIC280

Precision IttyBittyTM Thermal Supervisor

REV. 11/04

General Description

The MIC280 is a digital thermal supervisor capable of measur-

ing its own internal temperature and that of a remote PN junc-

tion. The remote junction may be an inexpensive commodity

transistor, e.g., 2N3906, or an embedded thermal diode such

as found in Intel Pentium* II/III/IV CPUs, AMD Athlon* CPUs,

and Xilinx Virtex* FPGA's. A 2-wire SMBus* 2.0 compatible

serial interface is provided for host communication. Remote

temperature is measured with ±1°C accuracy and 9-bit to

12-bit resolution (programmable). Independent high, low, and

over-temperature thresholds are provided for each zone.
The advanced integrating A/D converter and analog front-end

reduce errors due to noise for maximum accuracy and mini-

mum guardbanding. The interrupt output signals temperature

events to the host, including data-ready and diode faults.

Critical device settings can be locked to prevent changes and

insure failsafe operation. The clock, data, and interrupt pins

are 5V-tolerant regardless of the value of V

. They will not

clamp the bus lines low even if the device is powered down.

Superior accuracy, failsafe operation, and small size make

the MIC280 an excellent choice for the most demanding

thermal management applications.

Typical Application

DATA

SERIAL BUS

HOST

2N3906/

CPU DIODE

1800pF

MIC280

CLK
/INT

3V to 3.6V

3 ×

10k

VDD

GND

0.1µF

ceramic

MIC280 Typical Application

Features

· Measures local and remote temperature

· Highly accurate remote sensing

±1°C max., 60°C to 100°C

· Superior noise immunity for reduced temperature guard-

bands

· 9-bit to 12-bit temperature resolution for remote zone

· Fault queues to further reduce nuisance tripping

· Programmable high, low, and over-temperature thresh-

olds for each zone

· SMBus 2 compatible serial interface including device

timeout to prevent bus lockup

· Voltage tolerant I/O's

· Open-drain interrupt output pin - supports SMBus Alert

Response Address protocol

· Low power shutdown mode

· Locking of critical functions to insure failsafe operation

· Failsafe response to diode faults

· Enables ACPI compliant thermal management

· 3.0V to 3.6V power supply range

· IttyBittyTM SOT23-6 package

Applications

· Desktop, server and notebook computers

· Printers and copiers

· Test and measurement equipment

· Thermal supervision of Xilinx Virtex FPGA's

· Wireless/RF systems

· Intelligent power supplies

· Datacom/telecom cards

Micrel, Inc. · 2180 Fortune Drive · San Jose, CA 95131 · USA · tel + 1 (408) 944-0800 · fax + 1 (408) 474-1000 · http://www.micrel.com

IttyBiity is a trademark of Micrel, Inc.
*All trademarks are the property of their respective owners.

MIC280

Micrel

MIC280

November 2004

Pin Configuration

VDD

GND

/INT

DATA

CLK

SOT23-6

Pin Description

Pin Number

Pin Name

Pin Function

VDD

Power Supply Input.

GND

Ground.

Analog Input. Connection to remote diode junction.

CLK

Digital Input. Serial bit clock input.

DATA

Digital Input/Output. Open-drain. Serial data input/output.

/INT

Digital Output. Open-drain. Interrupt output.

Ordering Information

Part Number

Slave Address Ambient Temp. Range

Package

Standard

Marking Pb-FREE

Marking

MIC280-0BM6

TA00

MIC280-0YM6

TA00

100 1000

-55°C to +125°C

SOT23-6

MIC280-1BM6

TA01

MIC280-1YM6

TA01

100 1001

-55°C to +125°C

SOT23-6

MIC280-2BM6

TA02

MIC280-2YM6

TA02

100 1010

-55°C to +125°C

SOT23-6

MIC280-3BM6

TA03

MIC280-3YM6

TA03

100 1011

-55°C to +125°C

SOT23-6

MIC280-4BM6 TA04

MIC280-4YM6

TA05

100 1100

-55°C to +125°C

SOT23-6

MIC280-5BM6 TA05

MIC280-5YM6

TA05

100 1101

-55°C to +125°C

SOT23-6

MIC280-6BM6 TA06

MIC280-6YM6

TA06

100 1110

-55°C to +125°C

SOT23-6

MIC280-7BM6 TA07

MIC280-7YM6

TA07

100 1111

-55°C to +125°C

SOT23-6

November 2004

MIC280

Micrel

Absolute Maximum Ratings

(Note 1)

Power Supply Voltage, V

DD .....................................................

3.8V

Voltage on T1 ........................................0.3V to V

+0.3V

Voltage on CLK, DATA, /INT ..............................0.3V to 6V
Current Into Any Pin ................................................. ±10mA
Power Dissipation, T

= 125°C ................................ 109mW

Storage Temperature ................................ 65°C to +150°C
ESD Ratings,

Note 3

Human Body Model ................................................ 1.5kV

Machine Model ........................................................ 200V

Soldering (SOT23-6 Package)

Vapor Phase (60s) .....................................220°C

-0

°C

Infrared (15s) .............................................235°C

-0

°C

Operating Ratings

(Note 2)

Power Supply Voltage, V

............................ +3V to +3.6V

Ambient Temperature Range (T

) .......... 55°C to +125°C

Junction Temperature ................................................ 150°C
Package Thermal Resistance (

)

SOT23-6 ............................................................230°C/W

Electrical Characteristics

For typical values T

= 25°C, V

= 3.3V, unless otherwise noted.

Bold values indicate 55°C T

125°C, 3.0V V

3.6V,

unless otherwise noted. Note 2

Symbol

Parameter

Conditions

Min.

Typ

Max

Units

Power Supply
I

Supply Current

/INT, T1 open; CLK = DATA = High;

0.23

0.4

Normal Mode

Shutdown Mode; /INT, T1 open;

Note 5

CLK = 100kHz, DATA = High

Shutdown Mode; /INT, T1 open;

[TBD]

CLK = DATA = High

POR

Power-on Reset Time,

Note 5

> V

POR

200

POR

Power-on Reset Voltage

All registers reset to default values;

2.65

2.95

A/D conversions initiated

HYST

Power-on Reset Hysteresis Voltage

300

Note 5

Temperature-to-Digital Converter Characteristics

Accuracy, Remote Temperature

60°C T

100°C,

±0.25

±1

°C

Notes 2, 7, 10, 11

3.15V < V

< 3.45V, 25°C < T

< 85°C

0°C T

100°C,

±1

±2

°C

3.15V < V

< 3.45V, 25°C < T

< 85°C

55°C T

125°C,

±2

±4

°C

3.15V < V

< 3.45V, 25°C < T

< 85°C

Accuracy, Local Temperature

0°C T

100°C, 3.15V < V

< 3.45V

±1

±2

°C

Note 2, 10

55°C T

125°C, 3.15V < V

< 3.45V

±1.5

±2.5

°C

CONV

Conversion Time, Notes 2, 8

RES[1:0]=00 (9 bits)

200

240

RES[1:0]=01 (10 bits)

330

390

RES[1:0]=10 (11 bits)

570

670

RES[1:0]=11 (12 bits)

1000

1250

Remote Temperature Input, T1
I

Current into External Diode

T1 forced to 1.0V, High level

192

400

Note 5

Low level

MIC280

Micrel

MIC280

November 2004

Symbol

Parameter

Condition

Min

Typ

Max

Units

Serial Data I/O Pin, DATA
V

Low Output Voltage, Note 4

= 3mA

0.3

= 6mA

0.5

Low Input Voltage

3V V

3.6V

0.8

High Input Voltage

3V V

3.6V

2.1

5.5

Input Capacitance

Note 5

LEAK

Input Current

±1

Serial Clock Input, CLK
V

Low Input Voltage

3V V

3.6V

0.8

High Input Voltage

3V V

3.6V

2.1

5.5

Input Capacitance

Note 5

LEAK

Input Current

±1

Interrupt Output, /INT
V

Low Output Voltage, Note 4

= 3mA

0.3

= 6mA

0.5

INT

Interrupt Propagation Delay

from TEMPx < TLOWx or

CONV

]

Notes 5, 6

TEMPx > THIGHx or TEMPx >

CRITx to /INT < V

; R

PULLUP

= 10k

nINT

Interrupt Reset Propagation Delay

from read of STATUS or A.R.A. to

Note 5, 9

/INT > V

; R

PULLUP

= 10k

LEAK

±1

Serial Interface Timing
t

CLK (Clock) Period

2.5

µs

Data In Setup Time to CLK High

100

Data Out Stable after CLK Low

300

Data Low Setup Time to CLK Low

Start Condition

100

Data High Hold Time after CLK

Stop Condition

100

High

Bus Timeout

Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating range. Final test on outgoing product is performed at T

= 25°C.

Note 3. Devices are ESD sensitive. Handling precautions recommended.
Note 4. Current into the /INT or DATA pins will result in self heating of the device. Sink current should be minimized for best accuracy.
Note 5. Guaranteed by design over the operating temperature range. Not 100% production tested.
Note 6. t

INT

and t

CRIT

are equal to t

CONV

Note 7. T

is the temperature of the remote diode junction. Testing is performed using a single unit of one of the transistors listed in Table 8.

Note 8. t

CONV

= t

CONV

(local) + t

CONV

(remote). Following the acquisition of either remote or local temperature data, the limit comparisons for that zone

are performed and the device status updated; Status bits will be set and /INT driven active, if applicable.

Note 9. The interrupt reset propogation delay is dominated by the capacitance on the bus.
Note 10. Accuracy specification does not include quantization noise, which may be up to ±

LSB.

Note 11. Tested at 10-bit resolution.

MIC280

Micrel

MIC280

November 2004

Typical Characteristics

= 3.3V; T

= 25°C, unless otherwise noted.

-2.5

-2

-1.5

-1

-0.5

0.5

1.5

2.5

-55 -35 -15 5 25 45 65 85 105 125

MEASURMENT ERROR

(
°
C)

JUNCTION TEMPERATURE (°C)

A ccuracy vs .

T emperature, Internal S ens or

100

120

140

0 1 2 3 4 5 6 7 8 9 10

MEASURED LOCAL TEMPERATURE

(
°
C)

TIME (sec)

R es pons e to Immers ion

in 125°C F luid B ath

-20

-15

-10

-5

1000

2000

3000

4000

5000

6000

7000

8000

TEMPERATURE ERROR

(
°
C)

CAPACITANCE (pF)

R emote T emperature E rror vs .

C apacitanc e on T 1

-2

-1.5

-1

-0.5

0.5

1.5

100

MEASUREMENT ERROR

(
°
C)

REMOTE DIODE TEMPERATURE (°C)

R emote T emperature

Meas urement E rror

100

150

200

250

300

350

400

-55 -35 -15 5 25 45 65 85 105 125

SUPPLY CURRENT

(
µ
A)

TEMPERATURE (°C)

S upply C urrent vs .

T emperature for V

= 3.3V

-55 -35 -15 5 25 45 65 85 105 125

QUIESCENT CURRENT

(
µ
A)

TEMPERATURE (°C)

Quies c ent C urrent vs .

T emperature in S hutdown Mode

/INT , T 1 open

C LK = DAT A = HIG H

2.6

2.8

3.0

3.2

3.4

3.6

QUIESCENT CURRENT

(
µ
A)

SUPPLY VOLTAGE (V)

Quies c ent C urrent vs .

S upply V oltage in S hutdown Mode

/INT , T 1 open

C LK = DAT A = HIG H

100

200

300

400

QUIESCENT CURRENT

(
µ
A)

FREQUENCY (kHz)

Quies cent C urrent vs .

C loc k F requency in

S hutdown Mode

/INT , T 1 open

DAT A = HIG H

-8

-6

-4

-2

1x10

MEASUREMENT ERROR

(
°
C)

RESISTANCE FROM T1 ()

Meas urement E rror vs .

P C B L eakage to +3.3V /G ND

G ND

3.3V

REMOTE TEMP. ERROR

(
°
C)

Nois e Injected into the B as e of

R emote T rans is tor

FREQUENCY (Hz)

1 10 100 1k 10k 100k 1M 10M100M

3mV

P -P

25mV

P -P

10mV

P -P

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

TEMPERTURE ERROR

(
°
C)

Nois e Injected into the

C ollec tor of R emote T rans is tor

FREQUENCY (Hz)

1 10 100 1k 10k 100k 1M 10M100M

50mV

P -P

25mV

P -P

100mV

P -P

November 2004

MIC280

Micrel

Functional Description

Serial Port Operation
The MIC280 uses standard SMBus Write_Byte, Read_Byte,

and Read_Word operations for communication with its host.

The SMBus Write_Byte operation involves sending the

device's slave address (with the R/W bit low to signal a write

operation), followed by a command byte and the data byte.

The SMBus Read_Byte operation is a composite write and

read operation: the host first sends the device's slave address

followed by the command byte, as in a write operation. A

new start bit must then be sent to the MIC280, followed by a

repeat of the slave address with the R/W bit (LSB) set to the

high (read) state. The data to be read from the part may then

be clocked out. A Read_Word is similar, but two successive

data bytes are clocked out rather than one. These protocols

are shown in Figure 1, Figure 2, and Figure 3.
The Command byte is eight bits (one byte) wide. This byte

carries the address of the MIC280 register to be operated

upon. The command byte values corresponding to the vari-

ous MIC280 registers are shown in Table 1. Other command

byte values are reserved, and should not be used.
Slave Address
The MIC280 will only respond to its own unique slave ad-

dress. A match between the MIC280's address and the

address specified in the serial bit stream must be made to

initiate communication. The MIC280's slave address is fixed

at the time of manufacture. Eight different slave addresses

are available as determined by the part number. See Table

2 below and the Ordering Information table above.

Part Number

Slave Address

MIC280-0BM6

100 1000

= 48

MIC280-1BM6

100 1001

= 49

MIC280-2BM6

100 1010

= 4A

MIC280-3BM6

100 1011

= 4B

MIC280-4BM6

100 1100

= 4C

MIC280-5BM6

100 1101

= 4D

MIC280-6BM6

100 1110

= 4E

MIC280-7BM6

100 1111

= 4F

Table 2: MIC280 Slave Addresses

Alert Response Address
In addition to the Read_Byte, Write_Byte, and Read_Word

protocols, the MIC280 adheres to the SMBus protocol for

response to the Alert Response Address (ARA). The MIC280

expects to be interrogated using the ARA when it has as-

serted its /INT output.
Temperature Data Format
The least-significant bit of each temperature register (high

bytes) represents one degree Centigrade. The values are in

a two's complement format, wherein the most significant bit

Command Byte

Power-on

Target Register

Value

Default

Label

Description

Read

Write

TEMP0

Local temperature result

n/a

(0°C)

TEMP1h

Remote temperature result, high byte

n/a

(0°C)

STATUS

Status

n/a

CONFIG

Configuration

IMASK

Interrupt mask register

THIGH0

Local temperature high limit

(60°C)

TLOW0

Local temperature low limit

(0°C)

THIGH1h

Remote temperature high limit, high byte

(80°C)

TLOW1h

Remote temperature low limit, high byte

(0°C)

LOCK

Security register

TEMP1l

Remote temperature result, low byte

n/a

THIGH1l

Remote temperature high limit, low byte

TLOW1l

Remote temperature low limit, low byte

CRIT1

Remote over-temperature limit

(100°C)

CRIT0

Local over-temperature limit

(70°C)

MFG_ID

Manufacturer Identification

n/a

DEV_ID

Device and revision identification

n/a

* The lower nibble contains the die revision level, e.g., Rev 0 = 00h.

Table 1: MIC280 Register Addresses

MIC280

Micrel

MIC280

November 2004

(D7) represents the sign: zero for positive temperatures and

one for negative temperatures. Table 3 shows examples of

the data format used by the MIC280 for temperatures:

Temperature

Binary

Hex

+127°C

0111 1111

+125°C

0111 1101

+25°C

0001 1001

+1°C

0000 0001

0°C

0000 0000

1°C

1111 1111

25°C

1110 0111

125°C

1000 0011

128°C

1000 0000

Table 3: Digital Temperature Format, High Bytes

Extended temperature resolution is provided for the external

zone. The high and low temperature limits and the measured

temperature for zone one are reported as 12-bit values stored

in a pair of 8-bit registers. The measured temperature, for

example, is reported in registers TEMP1h, the high-order byte,

and TEMP1l, the low-order byte. The values in the low-order

bytes are left-justified four-bit binary values representing

one-sixteenth degree increments. The A-D converter resolu-

tion for zone 1 is selectable from nine to twelve bits via the

configuration register. Low-order bits beyond the resolution

selected will be reported as zeroes. Examples of this format

are shown below in Table 4.
FAULT QUEUE
A set of fault queues (programmable digital filters) are pro-

vided in the MIC280 to prevent false tripping due to thermal

or electrical noise. Two bits, CONFIG[5:4], set the depth of

the fault queues. The fault queue setting then determines

the number of consecutive temperature events (TEMPx >

THIGHx or TEMPx < TLOWx) which must occur in order for

the condition to be considered valid. As an example, as-

sume CONFIG[5:4] is programmed with 10b. The measured

temperature for a given zone would have to exceed THIGHx

for four consecutive A/D conversions before /INT would be

asserted or the status bit set.
Like any filter, the fault queue function also has the effect

of delaying the detection of temperature events. In this ex-

ample, it would take 4 x t

CONV

to detect a temperature event.

The fault queue depth vs. CONFIG[5:4] of the configuration

for over-temperature events (CRIT0 and CRIT1) or diode

faults. The fault queue applies only to high-temperature and

low-temperature events as determined by the THIGHx and

TLOWx registers. Any write to CONFIG will result in the fault

queues being purged and reset. Writes to any of the limit

registers, TLOWx or THIGHx, will result in the fault queue for

the corresponding zone being purged and reset.

CONFIG[5:4]

FAULT QUEUE

DEPTH

1 (Default)

Table 5: Fault Queue Depth Settings

Interrupt Generation
There are eight different conditions that will cause the MIC280

to set one of the bits in STATUS and assert its /INT output,

if so enabled. These conditions are listed in Table 6. Unlike

previous generations of thermal supervisor IC's, there are no

interdependencies between any of these conditions. That is,

if CONDITION is true, the MIC280 will respond accordingly,

regardless of any previous or currently pending events.
Normally when a temperature event occurs, the corresponding

status bit will be set in STATUS, the corresponding interrupt

mask bit will be cleared, and /INT will be asserted. Clearing

the interrupt mask bit(s) prohibits continuous interrupt gen-

eration while the device is being serviced. (It is possible to

prevent events from clearing interrupt mask bits by setting

bits in the lock register. See Table 7 for Lockbit function-

ality.) A temperature event will only set bits in the status

in the interrupt mask register. An interrupt signal will only

be generated on /INT if interrupts are also globally enabled

(IE =1 in CONFIG).
The MIC280 expects to be interrogated using the Alert Re-

sponse Address once it has asserted its interrupt output. Fol-

lowing an interrupt, a successful response to the A.R.A. or a

read operation on STATUS will cause /INT to be de-asserted.

STATUS will also be cleared by the read operation. Reading

STATUS following an interrupt is an acceptable substitute for

Extended Temperature,

Resolution

Low Byte

9 BITS

10 BITS

11 BITS

12 BITS

Binary

Hex

Binary

Hex

Binary

Hex

Binary

Hex

0.0000

0000 0000

0.0625

0000 0000

0001 0000

0.1250

0000 0000

0010 0000

0.2500

0000 0000

0100 0000

0.5625

1000 0000

1001 0000

0.9375

1000 0000

1100 0000

1110 0000

1111 0000

Table 4: Digital Temperature Format, Low Bytes

November 2004

MIC280

Micrel

D4
D5
D6

MIC280

S
l
a
v
e

r
es

A
T
A

CLK

ommand

y
t
e

a
ta

y
t
e

t
o MIC28

S
T
A

R
T

S
T
O

R/W = WRITE

CKN

WLEDG

CKN

WLEDG

CKN

WLEDG

t
er-

t
o-sl

a
v
e t

r
ansmissio

S
l
a
v
e-

t
o-mas

t
er

r
es

ons

Figure 1.

WRITE_BYTE Protocol

X
X
X

MIC280

S
l
a
v
e

r
es

A
T
A

CLK

ommand

y
t
e

MIC280

S
l
a
v
e

r
es

a
ta

R
ead

F
r
om MIC28

S
T
A

R
T

S
T
A

R
T

S
T
O

R/W = WRITE

R/W = READ

CKN

WLEDG

CKN

WLEDG

CKN

WLEDG

CKN

WLEDG

t
er-

t
o-sl

a
v
e t

r
ansmissio

S
l
a
v
e-

t
o-mas

t
er

r
es

ons

Figure 2.

READ_BYTE Protocol

MIC280

S
l
a
v
e

r
es

A
T
A

CLK

ommand

B
y
t
e

S
T
A

R
T

R/W = WRITE

CKN

WLEDG

CKN

WLEDG

D7
D8
D9

D10
D11

MIC280

S
l
a
v
e

r
es

High-O

r
der

B
y
t
e

(
TEMP1h)

f
r
om MIC28

L
o
w-O

r
der

B
y
t
e

(
TEMP1L

)

f
r
om MIC28

S
T
A

R
T

S
T
O

R/W = READ

CKN

WLEDG

CKN

WLEDG

CKN

WLEDG

t
er-

t
o-sl

a
v
e t

r
ansmissio

S
l
a
v
e-

t
o-mas

t
er

r
es

ons

Figure 3.

READ_WORD Protocol for

Accessing TEMP1h : TEMP1l

MIC280

Micrel

MIC280

November 2004

A2
1
0

0
1

r
t
R
es

onse

r
es

A
T
A

/INT

MIC280

r
es

ond wit

its sl

a
v
e add

r
es

S
T
A

R
T

INT

E
v
e
n

t
O

ccur

S
T
O

R/W = READ

CKN

WLEDG

CKN

WLEDG

INT

t
er-

t
o-sl

a
v
e t

r
ansmissio

S
l
a
v
e-

t
o-mas

t
er

r
es

ons

Figure 4.

MIC280

Alert Response

Address Protocol

0
0
0

0
0

MIC280

S
l
a
v
e

r
es

A
T
A

/INT

ommand

y
t
e = 03

ONFI

MIC280

S
l
a
v
e

r
es

V
alue in S

T
A
TUS*

S
T
A

R
T

INT

E
v
e
n

t
O

ccur

ll st

a
tus bits a

r
e clea

r
ed

t
o

z
e
r
o

f
oll

o
wing this o

e
r
a
tio

S
T
O

R/W = READ

CKN

WLEDG

CKN

WLEDG

CKN

WLEDG

t
er-

t
o-sl

a
v
e t

r
ansmissio

S
l
a
v
e-

t
o-mas

t
er

r
es

ons

INT

Figure 5.

Reading Status in response to an interrupt

November 2004

MIC280

Micrel

using the A.R.A. if the host system does not implement the

A.R.A protocol. Figure 4 and Figure 5 illustrate these two

methods of responding to MIC280 interrupts.
Since temperature-to-digital conversions continue while /INT

is asserted, the measured temperature could change between

the MIC280's assertion of /INT and the host's response. It

is good practice for the interrupt service routine to read the

value in TEMPx, to verify that the over-temperature or under-

temperature condition still exists. In addition, more than one

temperature event may have occurred simultaneously or in

rapid succession between the assertion of /INT and servic-

ing of the MIC280 by the host. The interrupt service routine

should allow for this eventuality. At the end of the interrupt

service routine, the interrupt enable bits should be reset to

permit future interrupts.
Reading the Result Registers
All MIC280 registers are eight bits wide and may be accessed

using the standard Read_Byte protocol. The temperature

result for the local zone, zone 0, is a single 8-bit value in

is sufficient for retrieving this value. The temperature result

for the remote zone is a twelve-bit value split across two

eight-bit registers, TEMP1h and TEMP1l. A series of two

Read_Byte operations are needed to obtain the entire twelve-

bit temperature result for zone 1. It is possible under certain

conditions that the temperature result for zone 1 could be

updated between the time TEMP1l or TEMP1h is read and

the companion register is read. In order to insure coherency,

TEMP1h supports the use of the Read_Word protocol for ac-

cessing both TEMP1h and TEMP1l with a single operation.

This insures that the values in both result registers are from

the same ADC cycle. This is illustrated in Figure 3 above.

Read_Word operations are only supported for TEMP1h:

TEMP1l, i.e., only for command byte values of 01h.
Polling
The MIC280 may either be polled by the host, or request

the host's attention via the /INT pin. In the case of polled

operation, the host periodically reads the contents of STA-

TUS to check the state of the status bits. The act of reading

STATUS clears it. If more than one event that sets a given

status bit occurs before the host polls STATUS, only the fact

that at least one such event has occurred will be apparent

to the host. For polled systems, the global interrupt enable

bit should be clear (IE = 0). This will disable interrupts from

the MIC280 (prevents the /INT pin from sinking current).

For interrupt-driven systems, IE must be set to enable the

/INT output.
Shutdown Mode
Putting the device into shutdown mode by setting the shutdown

bit in the configuration register will unconditionally deassert

/INT, clear STATUS, and purge the fault queues. Therefore,

this should not be done before completing the appropriate

interrupt service routine(s). No other registers will be affected

by entering shutdown mode. The last temperature readings

will persist in the TEMPx registers.
The MIC280 can be prevented from entering shutdown

mode using the shutdown lockout bit in the lock register. If

L3 in LOCK is set while the MIC280 is in shutdown mode,

it will immediately exit shutdown mode and resume normal

operation. It will not be possible to subsequently re-enter

shutdown mode. If the reset bit is set while the MIC280 is

shut down, normal operation resumes from the reset state.

(see below)
Warm Resets
The MIC280 can be reset to its power-on default state during

operation by setting the RST bit in the configuration register.

When this bit is set, /INT will be deasserted, the fault queues

will be purged, the limit registers will be restored to their normal

power-on default values, and any A/D conversion in progress

will be halted and the results discarded. This includes reset-

ting bits L3 - L0 in the security register, LOCK. The state of

the MIC280 following this operation is indistinguishable from

a power-on reset. If the reset bit is set while the MIC280 is

shut down, the shutdown bit is cleared and normal operation

resumes from the reset state.
If bit 4 of LOCK, the Warm Reset Lockout Bit, is set, warm

resets cannot be initiated, and writes to the RST bit will be

completely ignored. Setting L4 while the MIC280 is shut

down will result in the device exiting shutdown mode and

resuming normal operation, just as if the shutdown bit had

been cleared.

EVENT

CONDITION

MIC280 RESPONSE*

Data ready

A/D conversions complete for both zones; result

Set S7, clear IM7, assert /INT

registers updated; state of /INT updated

Over-temperature, remote

([TEMP1h:TEMP1l]) > CRIT1

Set S1, assert /INT

Over-temperature, local

TEMP0 > CRIT0

Set S0, assert /INT

High temperature, remote

([TEMP1h:TEMP1l]) > THIGH1h:THIGH1l]**

Set S4, clear IM4, assert /INT

High temperature, local

TEMP0 > THIGH0**

Set S6, clear IM6, assert /INT

Low temperature, remote

( [TEMP1h:TEMP1l]) < TLOW1h:TLOW1l]**

Set S3, clear IM3, assert /INT

Low temperature, local

TEMP0 < TLOW0**

Set S5, clear IM5, assert /INT

Diode fault

T1 open or T1 shorted to VDD or GND

Set S2, clear IM2, assert /INT

* Assumes interrupts enabled. **CONDITION must be true for Fault_Queue conversions to be recognized.

Table 6: MIC280 Temperature Events

MIC280

Micrel

MIC280

November 2004

Configuration Locking
The security register, LOCK, provides the ability to disable

configuration changes as they apply to the MIC280's most

critical functions: shutdown mode, and reporting diode faults

and over-temperature events. LOCK provides a way to prevent

malicious or accidental changes to the MIC280 registers that

might prevent a system from responding properly to critical

events. Once L0, L1, or L2 has been set, the global interrupt

enable bit, IE, will be set and fixed. It cannot subsequently be

cleared. Its state will be reflected in the configuration register.

The bits in LOCK can only be set once. That is, once a bit is

set, it cannot be reset until the MIC280 is power-cycled or a

warm reset is performed by setting RST in the configuration

L4 in LOCK. If L4 is set, locked settings cannot be changed

during operation and warm resets cannot be performed; only

a power-cycle will reset the locked state(s).
If L0 is set, the values of IM0 and CRIT0 become fixed and

unchangeable. That is, writes to CRIT0 and the corresponding

interrupt enable bit are locked out. A local over-temperature

event will generate an interrupt regardless of the setting of

IE or its interrupt mask bit.
If L1 is set, the values of IM1 and CRIT1 become fixed and

unchangeable. A remote over-temperature event will gener-

ate an interrupt regardless of the setting of IE or its interrupt

mask bit. Similarly, setting L2 will fix the state of IM2, allow-

ing the system to permanently enable or disable diode fault

interrupts. A diode fault will generate an interrupt regardless

of the setting of IE or its interrupt mask bit.
L3 can be used to lock out shutdown mode. If L3 is set, the

MIC280 will not shut down under any circumstances. Attempts

to set the SHDN bit will be ignored and all chip functions will

remain operational. If L3 is set while the MIC280 is in shutdown

mode, it will immediately exit shutdown mode and resume

normal operation. It will not be possible to subsequently re-

enter shutdown mode.
Setting L4 disables the RST bit in the configuration register,

preventing the host from initiating a warm reset. Writes to

RST will be completely ignored if L4 is set.

LOCK BIT

FUNCTION LOCKED

RESPONSE WHEN SET

Local over-temperature detection

IM0 fixed at 1, writes to CRIT0 locked-out; IE permanently set

Remote over-temperature detection

IM1 fixed at 1; writes to CRIT1 locked-out; IE permanently set

Diode fault interrupts locked on or off

IM2 fixed at current state; IE permanently set if IM2=1

Shutdown mode

SHDN fixed at 0; exit shutdown if SHDN=1 when L3 is set

Warm resets

RST bit disabled; cannot initiate Warm resets

Table 7: Lock bit functionality

November 2004

MIC280

Micrel

Local Temperature Result Register (TEMP0)

8-bits, read-only

Local Temperature Result Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read-only

Temperature Data from ADC

Bit

Function

Operation

D[7:0]

Measured temperature data for the local zone.

Read only

Power-up default value:

0000 0000

= 00

(0°C)**

Read command byte:

0000 0000

= 00

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. See Temperature Data Format (above) for more details.

**TEMP0 will contain measured temperature data after the completion of one conversion.

Remote Temperature Result High-Byte Register (TEMP1h)

8-bits, read only

Remote Temperature Result High-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read-only

Temperature Data from ADC

Bit

Function

Operation

D[7:0]

Measured temperature data for the remote zone, most significant byte.

Read only

Power-up default value:

0000 0000

= 00

(0°C)**

Read command byte:

0000 0001

= 01

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000b. See Temperature Data Format (above) for more details.
TEMP1h can be read using either a Read_Byte operation or a Read_Word operation. Using Read_Byte will yield the 8-bit

value in TEMP1h. The complete remote temperature result in both TEMP1h and TEMP1l may be obtained by performing a

Read_Word operation on TEMP1h. The MIC280 will respond to a Read_Word with a command byte of 01h (TEMP1h) by

returning the value in TEMP1h followed by the value in TEMP1l. This guarantees that the data in both registers is from the

same temperature-to-digital conversion cycle. The Read_Word operation is diagramed in Figure 3. This is the only MIC280

**TEMP1h will contain measured temperature data after the completion of one conversion.

Detailed Register Descriptions

MIC280

Micrel

MIC280

November 2004

Status Register (STATUS)

8-bits, read-only

Status Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read-only

Bit(s)

Function

Operation*

Data ready

1 = data available

0 = ADC busy

Local high temperature event

1 = event occurred, 0 = none

Local low temperature event

1 = event occurred, 0 = none

Remote high temperature event

1 = event occurred, 0 = none

Remote low temperature event

1 = event occurred, 0 = none

Diode fault

1 = fault, 0 = none

Remote over-temperature event

1 = event occurred, 0 = none

Local over-temperature event

1 = event occurred, 0 = none

* All status bits are cleared after any read operation is performed on STATUS.

Power-up default value:

0000 0000

= 00

(no events pending)

Read command byte:

0000 0010

= 02

The power-up default value is 00h. Following the first conversion, however, any of the status bits may be set depending on

the measured temperature results or the existence of a diode fault.

Configuration Register (CONFIG)

8-bits, read/write

Configuration Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

reserved

Interrupt

Shut-down

Fault Queue

Resolution

Reserved

Reset

Enable

(IE)

(SHDN)

(FQ[1:0])

(RES[1:0])

(RST)

Bits(s)

Function

Operation*

Interrupt enable

1 = interrupts enabled,

0 = disabled

SHDN

Selects operating mode: normal/shutdown

1 = shutdown, 0 = normal

FQ[1:0]

Depth of fault queue*

[00]=1, [01]=2, [10]=4, [11]=6

RES[1:0]

A/D converter resolution for external zone - affects conversion rate

[00]=9-bits, [01]=10-bits,

[10]=11-bits, [11]=12-bits

D[1]

Reserved

always write as zero!

RST

Resets all MIC280 functions and restores the power-up default state

write only; 1 = reset, 0 =

normal

operation; disabled by

setting L4

Power-up default value:

1000 0000

= 80

(Not in shutdown mode; Interrupts enabled;

Fault queue depth=1; Resolution = 9 bits)

Read/Write command byte:

0000 0011

= 03

* Any write to CONFIG will result in the fault queues being purged and reset and any A/D conversion in progress being aborted and the result

discarded. The A/D will begin a new conversion sequence once the write operation is complete.

November 2004

MIC280

Micrel

Interrupt Mask Register (IMASK)

8-bits, read/write

Interrupt Mask Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

IM7

IM6

IM 5

IM 4

IM 3

IM 2

IM 1

IM0

Bit(s)

Function

Operation*

IM7

Data ready event mask

1 = enabled, 0 = disabled

IM6

Local high temperature event mask

1 = enabled, 0 = disabled

IM5

Local low temperature event mask

1 = enabled, 0 = disabled

IM4

Remote high temperature event mask

1 = enabled, 0 = disabled

IM3

Remote low temperature event mask

1 = enabled, 0 = disabled

IM2

Diode fault mask

1 = enabled, 0 = disabled

IM1

Remote over-temperature event mask

1 = enabled, 0 = disabled

IM0

Local over-temperature event mask

1 = enabled, 0 = disabled

Power-up default value:

0000 0111

= 07

(Over-temp. and diode faults enabled)

Read/Write command byte:

0000 0100

= 04

Local Temperature High Limit Register (THIGH0)

8-bits, read/write

Local Temperature High Limit Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

High temperature limit for local zone.

Bit

Function

Operation

D[7:0]

High temperature limit for the local zone.

Read/write

Power-up default value:

0011 1100

= 3C

(60°C)

Read/Write command byte:

0000 0101

= 05

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. See Temperature Data Format (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

MIC280

Micrel

MIC280

November 2004

Local Temperature Low Limit Register (TLOW0)

8-bits, read/write

Local Temperature Low Limit Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

Low temperature limit for local zone

Bit

Function

Operation

D[7:0]

Low temperature limit for the local zone

Read/write

Power-up default value:

0000 0000

= 00

(0°C)

Read/Write command byte:

0000 0110

= 06

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. See TEMPERATURE DATA FORMAT (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

Remote Temperature High Limit High-Byte Register (THIGH1h)

8-bits, read/write

Remote Temperature High Limit High-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

High temperature limit for remote zone, most significant byte.

Bit

Function

Operation

D[7:0]

High temperature limit for the remote zone, most significant byte.

Read/write

Power-up default value:

0101 0000

= 50

(80°C)

Read/Write command byte:

0000 0111

= 07

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. See TEMPERATURE DATA FORMAT (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

November 2004

MIC280

Micrel

Remote Temperature Low Limit High-Byte Register (TLOW1h)

8-bits, read/write

Remote Temperature Low Limit High-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

Low temperature limit for remote zone, most significant byte.

Bit

Function

Operation

D[7:0]

Low temperature limit for the remote zone, most significant byte.

Read/write

Power-up default value:

0000 0000

= 00

(0°C)

Read/Write command byte:

0000 1000

= 08

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000b. See Temperature Data Format (above) for more details.
Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

Security Register (LOCK)

8-bits, write once

Security Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

reserved

read/

write-once

Reserved

Bit

Function

Operation*

D[7:5]

Reserved

Always write as zero

Warm reset lockout bit

1 = RST bit disabled;

0 = unlocked

Shutdown mode lockout bit*

1= shutdown disabled;

0 = unlocked

Diode fault event lock bit

1 = locked, 0 = unlocked

Remote over-temperature event lock bit

1 = locked, 0 = unlocked

Local over-temperature event lock bit

1 = locked, 0 = unlocked

Power-up default value:

0000 0000

= 00

(All events unlocked)

Read/Write command byte:

0000 1001

= 09

* If the chip is shutdown when L3 is set, the chip will exit shutdown mode and resume normal operation. It will not be possible to subsequently

re-enter shutdown mode.

MIC280

Micrel

MIC280

November 2004

Remote Temperature Result Low-Byte Register (TEMP1l)

8-bits, read only

Remote Temperature Result Low-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read-only

reserved

Temperature data from ADC, least significant bits

Reserved - always reads zero

Bit

Function

Operation

D[7:4]

Measured temperature data for the remote zone, least significant bits.

Read only

D[3:0]

Reserved

Always reads as zeroes

Power-up default value:

0000 0000

= 00

(0°C)**

Read command byte:

0001 0000

= 10

Each LSB represents one-sixteenth degree centigrade. The values are in a binary format such that 1/16th°C (0.0625°C) is

reported as 0001 0000

. See Temperature Data Format (above) for more details.

TEMP1l can be accessed using a Read_Byte operation. However, the complete remote temperature result in both TEMP1h

and TEMP1l may be obtained by performing a Read_Word operation on TEMP1h. The MIC280 will respond to a Read_Word

with a command byte of 01h (TEMP1h) by returning the value in TEMP1h followed by the value in TEMP1l. This guaran-

tees that the data in both registers is from the same temperature-to-digital conversion cycle. The Read_Word operation is

diagramed in Figure 3. TEMP1h is the only MIC280 register that supports Read_Word.
**TEMP1l will contain measured temperature data after the completion of one conversion.

Remote Temperature High Limit Low-Byte Register (THIGH1l)

8-bits, read/write

Remote Temperature High Limit Low-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

reserved

High temperature limit for remote zone, least significant bits.

Reserved - always reads zero

Bit

Function

Operation

D[7:4]

High temperature limit for the remote zone, least significant bits.

Read/write

D[3:0]

Reserved.

Always reads as zeros

Power-up default value:

0000 0000

= 00

(0°C)

Read/Write command byte:

0001 0011

= 13

Each LSB represents one-sixteenth degree centigrade. The values are in a binary format such that 1/16th°C (0.0625°C) is

reported as 0001 0000

. See Temperature Data Format (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

November 2004

MIC280

Micrel

Remote Temperature Low Limit Low-Byte Register (TLOW1l)

8-bits, read/write

Remote Temperature Low Limit Low-Byte Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

reserved

Low temperature limit for remote zone, least significant bits.

Reserved - always reads zero.

Bit

Function

Operation

D[7:4]

Low temperature limit for the remote zone, least significant bits.

Read/write

D[3:0]

Reserved

Always reads as zeros.

Power-up default value:

0000 0000

= 00

(0°C)

Read/Write command byte:

0001 0100

= 14

Each LSB represents one-sixteenth degree centigrade. The values are in a binary format such that 1/16th°C (0.0625°C) is

reported as 0001 0000

. See Temperature Data Format (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

Remote Over-Temperature Limit Register (CRIT1)

8-bit, read/write

Remote Over-Temperature Limit Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

Over-temperature limit for remote zone.

Bit

Function

Operation

D[7:0]

Over-temperature limit for the remote zone.

Read/write

Power-up default value:

0110 0100

= 64

(100°C)

Read/Write command byte:

0001 1001

= 19

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. SeeTemperature Data Format (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

MIC280

Micrel

MIC280

November 2004

Local Over-Temperature Limit Register (CRIT0)

8-bits, read/write

Local Over-Temperature Limit Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read/write

Over-temperature limit for local zone.

Bit

Function

Operation

D[7:0]

Over-temperature limit for the local zone.

Read/write

Power-up default value:

0100 0110

= 46

(70°C)

Read/Write command byte:

0010 0000

= 20

Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0°C is reported

as 0000 0000

. SeeTemperature Data Format (above) for more details.

Any writes to a temperature limit register will result in the corresponding fault queue being purged and reset.

Manufacturer ID Register (MFG_ID)

8-bits, read only

Manufacturer ID Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read only

BIT(S)

FUNCTION

Operation*

D[7:0]

Identifies Micrel as the manufacturer of the device. Always returns 2A

Read only. Always returns

Power-up default value:

0010 1010

= 2A

Read command byte:

1111 1110

= FE

Die Revision Register (DIE_REV)

8-bits, read only

Die Revision Register

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

read-only

reserved

MIC280 DIE REVISION NUMBER

Bit(s)

Function

Operation*

D[7:0]

Identifies the device revision number

Read only.

Power-up default value:

[Device revision number]

Read command byte:

1111 1111

= FF

November 2004

MIC280

Micrel

Application Information

Remote Diode Selection
Most small-signal PNP transistors with characteristics similar

to the JEDEC 2N3906 will perform well as remote temperature

sensors. Table 8 lists several examples of such parts that

Micrel has tested for use with the MIC280. Other transistors

equivalent to these should also work well.

Vendor

Part Number

Package

Fairchild Semiconductor

MMBT3906

SOT-23

On Semiconductor

MMBT3906L

SOT-23

Philips Semiconductor

PMBT3906

SOT-23

Samsung Semiconductor

KST3906-TF

SOT-23

Table 8: Transistors suitable for use as remote diodes

Minimizing Errors

Self-Heating

One concern when using a part with the temperature accuracy

and resolution of the MIC280 is to avoid errors induced by

self-heating (V

× I

) + (V

× I

). In order to understand

what level of error this might represent, and how to reduce

that error, the dissipation in the MIC280 must be calculated

and its effects reduced to a temperature offset. The worst-

case operating condition for the MIC280 is when V

= 3.6V.

The maximum power dissipated in the part is given in the

following equation:

= [(I

)+(I

OL(DATA)

)+(I

OL(/INT)

]

= [(0.4mA × 3.6V)+(6mA × 0.5V)+(6mA × 0.5V)]

= 7.44mW

(J-A)

of SOT23-6 package is 230°C/W

Theoretical Maximum T

due to self-heating is:

7.44mW × 230°C/W = 1.7112°C

Worst-case self-heating

In most applications, the /INT output will be low for at most

a few milliseconds before the host resets it back to the high

state, making its duty cycle low enough that its contribution to

self-heating of the MIC280 is negligible. Similarly, the DATA

pin will in all likelihood have a duty cycle of substantially below

25% in the low state. These considerations, combined with

more typical device and application parameters, give a better

system-level view of device self-heating in interrupt-mode

usage given in the following equation:

(0.23mA I

DD(typ)

3.3V) + (25% × 1.5mA I

OL(DATA)

0.15V)

+ (1% × 1.5mA I

OL(/INT)

0.15V) = 0.817mW

= (0.8175mW × 230°C/W) = 0.188°C

Real-world self-heating example

In any application, the best test is to verify performance

against calculation in the final application environment. This

is especially true when dealing with systems for which tem-

perature data may be poorly defined or unobtainable except

by empirical means.

Series Resistance

The operation of the MIC280 depends upon sensing the V

CB-E

of a diode-connected PNP transistor ("diode ") at two differ-

ent current levels. For remote temperature measurements,

this is done using an external diode connected between T1

and ground. Since this technique relies upon measuring the

relatively small voltage difference resulting from two levels of

current through the external diode, any resistance in series

with the external diode will cause an error in the temperature

reading from the MIC280. A good rule of thumb is this: for

each ohm in series with the external transistor, there will be

a 0.8°C error in the MIC280's temperature measurement. It is

not difficult to keep the series resistance well below an ohm

(typically < 0.1), so this will rarely be an issue.
Filter Capacitor Selection
It is usually desirable to employ a filter capacitor between the

T1 and GND pins of the MIC280. The use of this capacitor is

recommended in environments with a lot of high frequency

noise (such as digital switching noise), or if long wires are

used to conect to the remote diode. The maximum recom-

mended total capacitance from the T1 pin to GND is 2200pF.

This typically suggests the use of a 1800pF NP0 or C0G

ceramic capacitor with a 10% tolerance. If the remote diode

is to be at a distance of more than 6"-12" from the MIC280,

using twisted pair wiring or shielded microphone cable for

the connections to the diode can significantly reduce noise

pickup. If using a long run of shielded cable, remember to

subtract the cable's conductor-to-shield capacitance from the

2200pF maximum total capacitance.
Layout Considerations
The following guidelines should be kept in mind when design-

ing and laying out circuits using the MIC280:

1. Place the MIC280 as close to the remote diode

as possible, while taking care to avoid severe

noise sources such as high frequency power

transformers, CRTs, memory and data busses,

and the like.

2. Since any conductance from the various volt-

ages on the PC Board and the T1 line can in-

duce serious errors, it is good practice to guard

the remote diode's emitter trace with a pair of

ground traces. These ground traces should be

returned to the MIC280's own ground pin. They

should not be grounded at any other part of their

run. However, it is highly desirable to use these

guard traces to carry the diode's own ground

return back to the ground pin of the MIC280,

thereby providing a Kelvin connection for the

base of the diode. See Figure 6.

3. When using the MIC280 to sense the tempera-

ture of a processor or other device which has an

integral thermal diode, e.g., Intel's Pentium II, III,

IV, AMD Athlon CPU, Xilinx Virtex FPGAs, con-

nect the emitter and base of the remote sensor

to the MIC280 using the guard traces and Kelvin

return shown in Figure 6. The collector of the

remote diode is typically inaccessible to the user

MIC280

Micrel

MIC280

November 2004

on these devices. To allow for this, the MIC280

has superb rejection of noise appearing from

collector to GND.

4. Due to the small currents involved in the mea-

surement of the remote diode's V

, it is

important to adequately clean the PC board after

soldering to prevent current leakage. This is

most likely to show up as an issue in situations

where water-soluble soldering fluxes are used.

5. In general, wider traces for the ground and T1

lines will help reduce susceptibility to radiated

noise (wider traces are less inductive). Use trace

widths and spacing of 10 mils wherever possible

and provide a ground plane under the MIC280

and under the connections from the MIC280 to

the remote diode. This will help guard against

stray noise pickup.

REMOTE DIODE (T1)

GUARD/RETURN

VDD

GND

/INT

DATA

CLK

GUARD/RETURN

MIC280

Figure 6. Guard Traces/Kelvin Ground Returns

DATA

SERIAL BUS

HOST

2N3906/

CPU DIODE

1800pF

MIC280

CLK
/INT

3V to 3.6V

100

3 ×

10k

VDD

GND

0.1µF

ceramic

4.7µF

Figure 7. V

Decoupling for Very Noisy Supplies

6. Always place a good quality power supply

bypass capacitor directly adjacent to, or under-

neath, the MIC280. This should be a 0.1 µF ce-

ramic capacitor. Surface-mount parts provide the

best bypassing because of their low inductance.

7. When the MIC280 is being powered from par-

ticularly noisy power supplies, or from supplies

which may have sudden high-amplitude spikes

appearing on them, it can be helpful to add ad-

ditional power supply filtering. This should be

implemented as a 100 resistor in series with

the part's V

pin, and a 4.7 µF, 6.3V electrolytic

capacitor from V

to GND. See Figure 7.

November 2004

MIC280

Micrel

Package Information

0.20 (0.008)
0.09 (0.004)

0.60 (0.024)
0.10 (0.004)

3.00 (0.118)
2.80 (0.110)

10°

0°

3.00 (0.118)
2.60 (0.102)

1.75 (0.069)
1.50 (0.059)

0.95 (0.037) REF

1.30 (0.051)
0.90 (0.035)

0.15 (0.006)
0.00 (0.000)

DIMENSIONS:

MM (INCH)

0.50 (0.020)
0.35 (0.014)

1.90 (0.075) REF

6-Lead SOT23 (M6)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL

+ 1 (408) 944-0800

FAX

+ 1 (408) 474-1000

WEB

http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's

use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify

Micrel for any damages resulting from such use or sale.

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