October 2003

MIC2044/2045

Micrel

MIC2044/2045

Single Channel, High Current, Low Voltage,

Protected Power Distribution Switch

General Description

The MIC2044 and MIC2045 are high-side MOSFET switches
optimized for general purpose power distribution applications
that require circuit protection. These devices switch up to
5.5V and as low as 0.8V while offering both programmable
current limiting and thermal shutdown to protect the device
and the load. A fault status output is provided to indicate
overcurrent and thermal shutdown fault conditions. Both
devices employ soft-start circuitry to minimize the inrush
current in applications that employ highly capacitive loads.
Additionally, for tighter control over inrush current during start
up, the output slew-rate may be adjusted by an external
capacitor.

The MIC2045 features a auto-reset circuit breaker that latches
the output OFF upon detecting an overcurrent condition
lasting more than 32ms. The output is reset by removing or
reducing the load.

Data sheets and support documentation can be found on
Micrel's web site at www.micrel.com.

Typical Application

7, 11,

13, 16

9,12,14

SET

100W

Note:

All V

pins (7, 11, 13, 16) must be externally tied together.

All V

OUT

pins (9, 12, 14) must be externally tied together.

LIMIT

= 4A.

Output Power-Good = 3.0V.

*C4 is optional. See

"Applications Information."

C4*

0.022mF

0.1mF

Logic

Controller

ON/OFF

OVERCURRENT

MIC2044-1BTS

MIC39100-2.5BS

VBIAS

VIN

/FAULT

ILIM

SLEW

2.5V

VOUT

PGREF

PWRGD

UVLOIN

GND

20kW

294kW

24.3kW

GND

OUT

LOAD

33mF

OUT

3.3V@ 3.5A

20kW

(OPEN)

+3.3V

Power

Supply

OUT1

OUT2

4.7mF

0.1mF

Features

· 30m

maximum on-resistance

· 0.8V to 5.5V operating range
· Adjustable current limit
· Up to 6A continuous output current
· Short circuit protection
· Very fast reaction to short circuits
· Thermal shutdown
· Adjustable slew-rate control
· Circuit breaker mode (MIC2045)
· Fault status flag
· Power-Good detection
· Undervoltage lockout
· No reverse current flow through the switching MOSFET

when OFF or disabled

· Low quiescent current

Applications

· Docking stations
· LAN servers
· WAN switches
· Hot swap board insertions
· Notebook PCs
· PDAs
· Base stations
· RAID controllers
· USB hosts

Micrel, Inc. · 1849 Fortune Drive · San Jose, CA 95131 · USA · tel + 1 (408) 944-0800 · fax + 1 (408) 944-0970 · http://www.micrel.com

October 2003

MIC2044/2045

Micrel

Pin Description

Pin Number

Pin Name

Pin Function

PWRGD

Power-Good (Output): Open drain N-Channel device, active high. This pin
asserts high when the voltage at PGREF exceeds its threshold.

Switch Enable (Input): Gate control pin of the output MOSFET available as
an active high (1) or active low (2) input signal.

/FAULT

Fault Status (Output): Open drain N-Channel device, active low. This pin
indicates an overcurrent or thermal shutdown condition. For an overcurrent
event, /FAULT is asserted if the duration of the overcurrent condition lasts
longer than 32ms.

GND

Ground connection: Tie to analog ground.

SLEW

Slew-Rate Control (Input): A capacitor connected between this pin and
ground will reduce (slow) the output slew-rate. The output turn-on time must
be less than the nominal flag delay of 32ms in order to avoid nuisance
tripping of the /FAULT output since V

OUT

must be "fully on" (i.e., within

200mV of the voltage at the input) before the /FAULT signal delay elapses.
The slew-rate limiting capacitor requires a 16V rating or greater, 25V is
recommended. See

"Applications Information: Output Slew-Rate Adjust-

ment"

for further details.

ILIM

Current Limit (Input): A resistor (R

SET

) connected from this pin to ground

sets the current limit threshold as I

LIMIT

= CLF/R

SET

. CLF is the current limit

factor specified in the

"Electrical Characteristics"

table. For the MIC2044/45,

the continuous output current range is 1A to 6A.

UVLOIN

Undervoltage Lockout Adjust (Input): With this pin left open, the UVLO
threshold is internally set to 1.45V. When the switching voltage (V

) is at or

below 1.5V, connecting an external resistive divider to this input will lower the
UVLO threshold. The total resistance of the divider must be less than 200k

To disable the UVLO, tie this pin to VIN. See

"Applications Information"

for

further detail.

7,11,13,16

VIN

Switch Supply (Input): Connected to the drain of the output MOSFET. The
range of input for the switch is 0.8V to 5.5V. These pins must be externally
connected together to achieve rated performance.

9,12,14

VOUT

Switch (Output): Connected to the source of the output MOSFET. These
pins must be externally connected together to achieve rated performance.

VBIAS

Bias Supply (Input): This input pin supplies power to operate the switch and
internal circuitry. The input range for VBIAS is 1.6V to 5.5V. When switched
voltage (V

) is between 1.6V to 5.5V and the use of a single supply is

desired, connect VBIAS to VIN externally.

PGREF

Power-Good Threshold (Input): Analog reference used to specify the
PWRGD threshold. When the voltage at this pin exceeds its threshold, V

PWRGD is asserted high. An external resistive divider network is used to
determine the output voltage level at which V

is exceeded. See the

"Functional Description"

for further detail. When the PWRGD signal is not

utilized, this input should be tied to VOUT.

MIC2044/2045

Micrel

MIC2044/2045

October 2003

Absolute Maximum Ratings

(Note 1)

and V

BIAS ..................................................................................

/FAULT, PWRGD Output Voltage ................................... 6V

/FAULT, PWRGD Output Current .............................. 25mA

ESD Rating, Note 3

Human Body Model ................................................... 2kV
Machine Model ........................................................ 200V

Operating Ratings

(Note 2)

Supply Voltage

............................................................... 0.8V to 5.5V

BIAS

........................................................... 1.6V to 5.5V

Continuous Output Current ................................... 1A to 6A

Ambient Temperature (T

) ........................... 40

C to 85

Package Thermal Resistance

(

(J-A)

)

TSSOP ................................................................ 85

C/W

Electrical Characteristics

(Note 4)

= V

BIAS

= 5V, T

= 25

C unless specified otherwise. Bold indicates 40

C to +85

Symbol

Parameter

Condition

Min

Typ

Max

Units

Switch Input Voltage

BIAS

0.8

5.5

BIAS

Bias Supply Voltage

1.6

5.5

BIAS

Supply Current - Switch OFF

No load

0.1

BIAS

Supply Current - Switch ON

No load

300

400

Note 5

Enable Input Voltage

IL(max)

2.4

1.5

IH(min)

3.5

2.5

ENHYST

Enable Input Threshold Hysteresis

100

Enable Input Current

= 0V to 5.5V

.01

DS(ON)

Switch Resistance

= V

BIAS

= 3V, 5V

OUT

= 500mA

LEAK

Output Leakage Current

Output off

CLF

Current Limit Factor

= 3V, 5V, 0.5V

OUT

< 0.5V

300

380

460

A·

Note 6

OUT

PGREF Threshold

= V

BIAS

= 1.6V to 5.5V

215

230

245

LATCH

Output Reset Threshold

= 0.8V to 5.5V

.0.2

OUT

rising (MIC2045)

LATCH

Latched Output Off Current

Output latched off (MIC2045)

Output Low Voltage

(/FAULT) = 15mA

0.4

(/FAULT, PWRGD)

(PWRGD) = 5mA

OFF

/FAULT, PWRGD Off Current

FAULT

= V

PWRGD

= 5V

Undervoltage Lockout Threshold

rising

1.30

1.45

1.58

falling

1.20

1.35

1.50

UVHYST

Undervoltage Lockout

100

Threshold Hysteresis

UVINTH

UVLO Adjust Pin Threshold Voltage

rising

200

230

260

falling

185

215

245

UVINHYST

UVLO Adjust Pin Threshold Hysteresis

Overtemperature Threshold

increasing

140

decreasing

120

October 2003

MIC2044/2045

Micrel

Symbol

Parameter

Condition

Min

Typ

Max

Units

FLAG

Flag Response Delay

= V

BIAS

= 3V, 5V

Output Turn-on Delay

LOAD

= 10

, C

LOAD

= 1

0.75

1.25

Output Turn-on Rise Time

LOAD

= 10

, C

LOAD

= 1

1.5

2.5

3.5

OFF

Output Turn-off Delay

LOAD

= 10

, C

LOAD

= 1

Output Turn-off Fall Time

LOAD

= 10

, C

LOAD

= 1

Note 1.

Exceeding the absolute maximum rating may damage the device.

Note 2.

The device is not guaranteed to function outside its operating rating.

Note 3.

Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5k

in series with 100pF.

Note 4.

Specification for packaged product only.

Note 5.

OFF is V

< 1.0V for MIC2044/MIC20451 and V

> 4.0V for MIC2044/MIC2045 2. ON is V

> 4.0V for MIC2044/MIC20451 and

< 1.0V for MIC2044/MIC2045 2.

Note 6.

The current limit is determined as follows: I

LIM

= CLF/R

SET

Timing Diagrams

50%

(a) MIC2044/45-1

(b) MIC2044/45-2

10%

90%

OFF

OUT

50%

10%

90%

OFF

OUT

Figure 1. Turn-On/Turn-Off Delay

LIMIT

OUT

/FAULT

FLAG

0.2V

Increase the load

Figure 2. Overcurrent Fault Response -- MIC2044-2

October 2003

MIC2044/2045

Micrel

100

125

150

175

200

225

250

275

300

-40 -20

80 100

SUPPLY CURRENT (

TEMPERATURE (

Supply Current

vs. Temperature

= V

BIAS

= 1.6V

= V

BIAS

= 5.5V

= V

BIAS

= 3V

-40 -20

80 100

(V)

TEMPERATURE (

Enable Input Threshold

(Rising)

vs. Temperature

BIAS

= 5.5V

BIAS

= 3V

BIAS

= 1.6V

-40 -20

80 100

(V)

TEMPERATURE (

Enable Input Threshold

(Falling)

vs. Temperature

BIAS

= 5.5V

BIAS

= 3V

BIAS

= 1.6V

250

500

750

1000

1250

1500

1750

2000

2250

2500

-40 -20

80 100

OUTPUT LEAKAGE (nA)

TEMPERATURE (

Output Leakage Current

vs. Temperature

BIAS

= 5.5V

BIAS

= 3V

BIAS

= 1.6V

-40 -20

80 100

ON RESISTANCE (m

)

TEMPERATURE (

ON Resistance

vs. Temperature

= V

BIAS

= 1.6V

= V

BIAS

= 3V

= V

BIAS

= 5.5V

-40 -20

80 100

FLAG

(ms)

TEMPERATURE (

Flag Response Delay

vs. Temperature

FLAG

= 3V

FLAG

= 5V

200

400

600

800

1000

1200

1400

1600

-40 -20

80 100

TURN ON DELAY (

TEMPERATURE (

Turn On Delay

vs. Temperature

= V

BIAS

= 5.5V

= V

BIAS

= 3V

= V

BIAS

= 1.6V

(mA)

OUT

BIAS

(V)

BIAS

Reverse Current Flow

vs. Output Voltage

= GND

BIAS

= 1.6V

Typical Characteristics

0.5

1.5

2.5

-40 -20

80 100

UVLO THRESHOLD (V)

TEMPERATURE (

UVLO Threshold

vs. Temperature

UVLO+

UVLO

100

150

200

250

300

350

400

-40 -20

80 100

UVLOIN THRESHOLD (mV)

TEMPERATURE (

UVLO Adjust Pin Threshold

vs. Temperature

UVLOIN+

UVLOIN

-40 -20

80 100

SLEW PIN VOLTAGE (V)

TEMPERATURE (

SLEW Voltage

vs. Temperature

= V

BIAS

= 1.6V

= V

BIAS

= 5V

= V

BIAS

= 3V

210

215

220

225

230

-40 -20

80 100

(mV)

TEMPERATURE (

Power-Good Reference

Threshold

vs. Temperature

@ 1.6V to 5.5V

MIC2044/2045

Micrel

MIC2044/2045

October 2003

Functional Characteristics

OUT

2A/div

PWRGD 5V/div

OUT

2V/div

5V/div

= V

BIAS

= 5.0V

LOAD

= 1.65W

LOAD

= 47mF

SET

= 100W

5V Turn-On

TIME (1ms/div.)

OUT

2A/div

PWRGD 5V/div

OUT

5V/div

= V

BIAS

= 5.0V

LOAD

= 1.65V

LOAD

= 47mF

SET

= 100W

5V Turn-Off

TIME (500ms/div.)

OUT

2A/div

OUT

5V/div

AUL

5V/div

= V

BIAS

5.0V

LOAD

1.8

LOAD

SET

220

Latched Output

MIC2045

TIME (5ms/div.)

OUT

2V/div

AUL

5V/div

= V

BIAS

5.0V

LOAD

toggles from 2

to OPEN

LOAD

SET

220

4.82V

Latched Output Reset

MIC2045

TIME (50ms/div.)

OUT

200mA/div

1V/div

OUT

1V/div

ramps 0V to 1.8V

LOAD

SET

220

UVLO Response

TIME (2.5ms/div.)

1.45V

OUT

2A/div

AUL

5V/div

OUT

2V/div

= V

BIAS

5.0V

LOAD

1.2

LOAD

SET

100

Current Limit Response

TIME (5ms/div.)

October 2003

MIC2044/2045

Micrel

Functional Description

The MIC2044 and MIC2045 are high-side N-Channel switches
equipped with programmable current limit up to 6A for use in
general purpose power distribution applications. The switches,
available with active-high or active-low enable inputs, provide
output slew-rate control and circuit protection via thermal
shutdown and an optional output latch during overcurrent
conditions.

Input and Output

VBIAS supplies power to the internal circuitry of the switch
and must be present for the switch to operate. VIN is con-
nected to the drain of the output MOSFET and sources power
to the switched load. VIN must be less than or equal to VBIAS.
VOUT is the source terminal of the output MOSFET and
attaches to the load. In a typical circuit, current flows from VIN
to VOUT toward the load. If VOUT is greater than VIN, current
will flow from VOUT to VIN since the switch is bi-directional
when the device is enabled. When disabled (OFF), the switch
will block current flow from either direction.

Enable Input

Enable, the ON/OFF control for the output switch, is a digital
input available as an active-high (1) or active-low (2)
signal. The EN pin, referenced to approximately 0.5

VBIAS,

must be driven to a clearly defined logic high or logic low.
Failure to observe this requirement, or allowing EN to float,
will cause the MIC2044/45 to exhibit unpredictable behavior.
EN should not be allowed to go negative with respect to
ground, nor allowed to exceed VBIAS. Failure to adhere to
these conditions may result in damage to the device.

Undervoltage Lockout

When the switch is enabled, undervoltage lockout (UVLO)
monitors the input voltage, V

, and prevents the output

MOSFET from turning on until V

exceeds a predetermined

level, nominally set at 1.45V. The UVLO threshold is adjust-
able and can be varied by applying an external resistor divider
to the UVLOIN pin from VIN to GND. The resistive divider
network is required when the input voltage is below 1.5V. The
UVLO threshold is internally preset to 1.45V if the UVLOIN
pin is left open. See

"Applications Information."

Programmable Current Limit

The MIC2044/45 is designed to prevent damage to the
external load by limiting the maximum amount of current it
can draw. The current limit is programmed by an external
resistor (R

SET

) connected from ILIM (Pin 6) to ground and

becomes active when the output voltage is at least 200mV
below the voltage at the input to the device. The limiting
current value is defined by the current limit factor (CLF)
divided by R

SET

, and the MIC2044/45 will limit from 1A to 6A

with a set point accuracy of

21%. In programming the

nominal current limit, the value of R

SET

is determined using

the following equation:

CLF

380A

SET

LIMIT

(

)

(1)

And given the

21% tolerance of the current limit factor (CLF),

the external resistor is bound by:

SET

460

(2)

The graphs below (Figure 3) display the current limit factor
characteristic over the full temperature range at the indicated
voltage. These curves can be used as a point of reference in
determining the maximum variation in the device's current
limit over the full temperature range. For example: With V

= V

BIAS

= 3.0V and a nominal 4A current limit (R

SET

= 95

the low and high current limit settings for the MIC2044/45
would be 3.15A and 4.85A, respectively, as shown on the 3V
graph using the 95

reference point.

When current limiting occurs, the MIC2044 and MIC2045
respond differently. Upon first reaching the limiting current
both devices restrict current flow, allowing the load voltage to
drop below V

. If the V

to V

OUT

differential voltage exceeds

200mV, then a fault condition is declared and the fault delay
timer is started. If the fault condition persists longer than the
delay period, typically 32ms, then the /FAULT output asserts
low. At this point, the MIC2044 will continue to supply current
to the load at the limiting value (I

LIMIT

), whereas the MIC2045

will latch off its output.

50 100 150 200 250 300 350 400 450

LIMIT

(A)

SET

(

)

Current Limit

vs. R

SET

C to +85

= V

BIAS

= 3V, 5V

CLF (LO)

CLF (HI)

50 100 150 200 250 300 350 400 450

LIMIT

(A)

SET

(

)

Current Limit

vs. R

SET

C to +85

= V

BIAS

= 1.6V

CLF (LO)

CLF (HI)

Figure 3. Current Limit Factor

MIC2044/2045

Micrel

MIC2044/2045

October 2003

/FAULT

The /FAULT signal is an N-Channel, open-drain MOSFET
output. An external pull-up resistor tied to a maximum 6V rail
is required for the /FAULT pin. The /FAULT pin is asserted
(active-low) when either an overcurrent or thermal shutdown
condition occurs. During a hot insert of a PCB or when turning
on into a highly capacitive load, the resulting high transient
inrush current may exceed the current limit threshold of the
MIC2044/45. In the case where an overcurrent condition
occurs, /FAULT will assert only after the flag delay time has
elapsed, typically 32ms. This ensures that /FAULT is as-
serted only upon valid overcurrent conditions and that nui-
sance error reporting is prevented.

Thermal Shutdown

For the MIC2044, thermal shutdown is employed to protect
the device from damage should the die temperature exceed
safe margins due to a short circuit or an excessive load.
Thermal shutdown shuts off the output MOSFET and asserts
the /FAULT output if the die temperature exceeds 140

The MIC2044 automatically resets its output and resumes
supplying current to the load when the die temperature drops
to 120

C. If the fault is still present, the MIC2044 will quickly

re-heat and shut down again. This process of turning
ON-OFF-ON is called thermal cycling and will continue as
long as the power switch is enabled while the fault or
excessive load is present.

Depending on PCB layout (including thermal considerations
such as heat sinking), package, and ambient temperature, it
may take several hundred milliseconds from the incidence of
the fault to the output MOSFET being shut off.

Circuit Breaker Function (MIC2045)

The MIC2045 is designed to shut off all power to the load
when a fault condition occurs, just as a circuit breaker would
do. In this case, a fault condition is deemed to be anytime the
output current exceeds the current limit for more than the flag
delay period, nominally 32ms. Once the output shuts off, it
remains off until either the fault load is removed from VOUT
or the EN input is cycled ON-OFF-ON. If the fault is still
present after EN has been cycled, the MIC2045 will again
shut off all power to the load after 32ms. Once the fault has
been removed, then normal operation will resume.

Open Load Detection

The MIC2045 will automatically reset its output when the fault
load is cleared. This is accomplished by applying a small
current to VOUT and watching for the voltage at VOUT to rise
to within 200mV of VIN. This current is supplied by an internal
resistor connected to VIN and is connected to VOUT when
MIC2045 latches off.

Power-Good Detection

The MIC2044/45 can detect when the output voltage is above
or below a preset threshold that is monitored by a comparator
at the PGREF input. The PWRGD signal is an N-Channel
open-drain MOSFET output and an external pull-up resistor
up to a 6V maximum rail is required for the PWRGD pin.
Whenever the voltage at the PGREF pin exceeds its thresh-
old (V

), typically 230mV, the PWRGD output is asserted.

Using the typical applications circuit from page 1 that switches
3.3V as an example, the output voltage threshold determin-
ing "power is good" is calculated by the following equation:

OUT(GOOD)

× +

(3)

In substituting the resistor values of the circuit and the typical
PGREF threshold, the resulting V

OUT(GOOD)

is calculated as

3.0V for this 3.3V switching application.

SLEW

The MIC2044/45's output rise time is controlled at turn-on to
a minimum of 1.5ms and is controlled by an internal slew-rate
limiting circuit. A slew-rate adjustment control pin is available
for applications requiring slower rise times. By placing a
capacitor between SLEW and ground, longer rise times can
be achieved. For further detail, see the

"Applications Informa-

tion"

section.

October 2003

MIC2044/2045

Micrel

Applications Information

Input and Output

Supply Bypass Filtering

The need for input supply bypass is brought about due to
several factors, most notably the input/output inductance
along the power path, operating current and current limit, and
output capacitance. A 0.1

F to 0.47

F bypass capacitor

positioned very close to the VIN pin to GND of the device is
strongly recommended to filter high frequency oscillations
due to inductance. Also, a sufficient bypass capacitor posi-
tioned close to the input source to the switch is strongly
advised in order to suppress supply transient spikes and to
limit input voltage droop. Inrush current increases with larger
output capacitance, thus the minimum value of this capacitor
will require experimental determination for the intended appli-
cation and design. A good starting point is a capacitor
between 4.7

F to 15

F. Without these bypass capacitors, an

extreme overload condition such as a short circuit, or a large
capacitive load, may cause either the input supply to exceed
the maximum rating of 6V and possibly cause damage to the
internal control circuitry or allow the input supply to droop and
fall out of regulation and/or below the minimum operating
voltage of the device.

Output Capacitance

When the MIC2044 die exceeds the overtemperature thresh-
old of approximately 140

C, the device can enter into a

thermal shutdown mode if the die temperature falls below
120

C and then rises above 140

C in a continuous cycle.

With VOUT cycling on and off, the MIC2044 will reset the
/FAULT while in an overtemperature fault condition if V

OUT

allowed to swing below ground. The inductance present at
the output must be neutralized by capacitance in order to
ensure that the output does not fall below ground. In order to
counter the board parasitic inductance and the inductance of
relatively short-length power cable (

1ft., 16 - 20 gauge wire),

a minimum output capacitance of 22

F is strongly recom-

mended and should be placed close to the VOUT pin of the
MIC2044. For applications that use more than a foot of cable,
an additional 10

F/ft. is recommended.

Reverse Current Blocking

The MIC2044/45 provides reverse current flow blocking
through the output MOSFET if the voltage at VOUT is greater
than VIN when the device is disabled. The V

BIAS

supply has

a limited reverse current flow if the voltage at VOUT is pulled
above VBIAS when the device is disabled. A graph of the
V

BIAS

reverse current flow is shown in the

"Functional

Characteristics"

section. The reverse current for VBIAS can

be completely blocked by inserting a Schottky diode from the
VBIAS pin (cathode) to the supply (anode). However, the
minimum voltage of 1.6V must be supplied to VBIAS after
accounting for the voltage drop across the diode.

Output Slew-Rate Adjustment

The output slew-rate for the MIC2044/45 can be slowed down
by the use of a capacitor (16V rating, minimum; 25V sug-
gested) between SLEW and GND. The slew-rate control
circuitry is independent of the load capacitance and exhibits

a non-linear response. See the

"Functional Characteristics"

section. Table 1 shows the rise time for various standard
capacitor values. Additionally, the output turn-on time must
be less than the nominal flag delay of 32ms in order to avoid
nuisance tripping of the /FAULT output. This limit is imposed
by the current limiting circuitry which monitors the
(VIN VOUT) differential voltage and concludes a fault
condition is present if the differential voltage exceeds 200mV
for more than the flag delay period. For the MIC2045, the
/FAULT will assert and the output will latch off if the output is
not within 200mV of the input before the flag delay times out.
When using the active-low (2) option with the EN input tied
to ground, slew control is functional during initial start-up but
does not function upon resetting the input power to the
device. In order for the SLEW control to operate during
consecutive system restarts, the EN pin must reset (toggle
OFF to ON).

UVLO Threshold Setting With Low Input Voltages

When the switching voltage is below 1.6V, the device's
standard UVLO threshold (1.45V nominal) will hinder the
output MOSFET in switching VIN to VOUT. In this case, the
use of the UVLOIN pin is required to override the standard
UVLO threshold and set a new, lower threshold for the lower
input voltage. An external resistive divider network con-
nected at the UVLOIN pin is used to set the new threshold.
Due to the ratio of the internal components, the total series
resistance of the external resistive divider should not exceed
200k

. The circuit shown in Figure 4 illustrates an application

that switches 0.8V while the device is powered from a
separate 2.5V power supply. The UVLO threshold is set by
the following equation.

0.23V

UVTH

× +

(4)

In substituting the resistor values from Figure 4, the resulting
UVLO threshold (V

UVTH

) is calculated as 0.6V for this 0.8V

switching application. When using the UVLOIN pin to set a
new UVLO threshold, an optional 0.1

F to 1.0

F capacitor

from UVLOIN to GND may be used as a glitch filter in order
to avoid nuisance tripping of the UVLO threshold. If the
UVLOIN pin is not in use, this pin should be left open
(floating). The use of a pull-down resistor to ground will offset
the ratio of the internal resistive divider to this pin resulting in
a shift in the UVLO threshold. To bypass (disable) UVLO,
connect the UVLOIN pin directly to the VIN pin of the
MIC2044/45.

Conditions: V

= V

BIAS

= 5V/3V

LOAD

= 47

F; I

LOAD

= 1A

SLEW

(

Rise Time (ms)

0.02

4.4

6.6

0.033

7.5

11.25

0.047

0.1

31.5

Table 1. Typical Output Rise Time for Various C

SLEW

= 5V, 3V)

MIC2044/2045

Micrel

MIC2044/2045

October 2003

7,11,

13,16

9,12,14

SET

200W

0.1mF

MIC2044-1BTS

VBIAS

VIN

/FAULT

UVLOIN

SLEW

VOUT

PGREF

PWRGD

ILIM

GND

47kW

75kW

1%
R5

36.5kW

LOAD

22mF

OUT

0.8V @1.5A

47kW

Digital

Output

Signals

10mF

0.1mF

0.8V

2.5V

95.3kW

59.0kW

47kW

Note:

All V

pins (7, 11, 13, 16) must be externally tied together.

All V

OUT

pins (9, 12, 14) must be externally tied together.

Undervoltage Lockout = 0.6V.

Output Power-Good = 0.7V.

Figure 4. Lower UVLO Setting

Power Dissipation

Power dissipation depends on several factors such as the
load, PCB layout, ambient temperature, and package type.
The following equations can be used to calculate power
dissipation and die temperature.

Calculation of power dissipation can be accomplished by the
following equation:

= R

DS(on)

OUT

)

(5)

To relate this to junction temperature, the following equation
can be used:

= P

(

J-A)

+ T

(6)

where T

= junction temperature, T

= ambient temperature

and R

(J-A)

is the thermal resistance of the package.

Printed Circuit Board Hot Plug

The MIC2044/45 are ideal inrush current limiting power
switches suitable for hot plug applications. Due to the inte-
grated charge pump, the MIC2044/45 present a high imped-
ance when in the off state and the device slowly becomes a
low impedance as it turns on. This effectively isolates power
supplies from highly capacitive loads by reducing inrush
current during hot plug events. This same feature also can be
used for soft-start requirements.

PCB Layout Recommendations

The MIC2044 and MIC2045 have very low on-resistance,
typically 20m

, and the switches can provide up to 6A of

continuous output current. Under heavy loads, the switched
current may cause the devices to heat up considerably. The
following list contains some useful suggestions for PCB
layout design of the MIC2044/45 in order to prevent the die
from overheating under normal operating conditions.

Micrel Semiconductor does not assume responsibility for the use of
this program tool in the event that any PCB assembled, tested,
produced, and/or manufactured becomes damaged and/or causes any
degradation of system performance or damage to any system
components in which the aforementioned PCB is included.

1. Supply additional copper area under the device

to remove heat away from the IC.

See

"Application Hint 17"

for a general guideline

in calculating the suggested area.

2. Provide additional pad area on the corner pins of

the MIC2044/45 IC for heat distribution.

3. Tie the common power pins (V

= pins 7, 11,

13, 16 and V

OUT

= pins 9, 12, 14) together in a

manner such that the traces entering and
leaving the device have a uniform width suffi-
cient for the application's current requirements
plus added margin (25% minimum recom-
mended).

Ex: For 4A maximum current, design traces for
5A capability.

4. For PCB trace width calculation, there are

numerous calculator programs available on the
internet and elsewhere. As a general rule of
thumb, 15-20 mils width for every 1A of current
when using 1oz. copper. However, the trace
width calculators often take into account maxi-
mum temperature increase constraints, as well
as layer arrangement, in determining the PCB
trace widths. As a reference, the following link is
suggested for trial tests in PCB trace width
calculations.

http://www.aracnet.com/cgi-usr/gpatrick/trace.pl

October 2003

MIC2044/2045

Micrel

Package Information

Rev. 01

16-Pin TSSOP (TS)

MICREL, INC.

1849 FORTUNE DRIVE

SAN JOSE, CA 95131

USA

TEL

+ 1 (408) 944-0800

FAX

+ 1 (408) 944-0970

WEB

http://www.micrel.com

The information furnished by Micrel in this datasheet 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 at Purchaser's own risk and Purchaser agrees to fully indemnify

Micrel for any damages resulting from such use or sale.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MIC2045-2BTS

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MIC2045-2BTS