January 2004
1
M9999-012004
MIC2040/2041
Micrel
MIC2040/2041
Single Channel Low Voltage Power Distribution Switch
General Description
The MIC2040 and MIC2041 are high side MOSFET switches
optimized for general purpose power distribution applications
that require circuit protection. The 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 in order to detect
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, the MIC2040/41 is suited for multi-port USB
applications to satisfy upstream/downstream power require-
ments.
The MIC2041 features a auto-reset circuit breaker mode that
latches the output off upon detecting an overcurrent condition
lasting more than 28ms. 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, 9
6
1
2
5
8,10
3
R
SET
340
Note:
BothV
IN
pins (7, 8) must be externally tied together.
BothV
OUT
pins (8, 10) must be externally tied together.
I
LIMIT
= 1A.
C3
4.7
F
Logic
Controller
ON/OFF
OVERCURRENT
IN
4
MIC2040-1BM
VBIAS
VIN
EN
/FAULT
ILIM
VOUT
UVLOIN
GND
+3.3V
Power
Supply
R1
20k
C
LOAD
33
F
(OPEN)
V
OUT
3.3V@ 1A
C2
0.1
F
C1
0.1
F
Features
75m max. on-resistance
0.8V to 5.5V operating range
Adjustable current limit
Up to 1.5A continuous output current
Short circuit protection with thermal shutdown
Circuit breaker mode (MIC2041)
Fault status flag
Undervoltage lockout
Output MOSFET reverse current flow block when
disabled
Very fast reaction to short-circuits
Low quiescent current
Applications
Docking stations
Notebook PCs
PDAs
Board hot swap
RAID controllers
USB peripherals
ACPI power distribution
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
Ordering Information
Part Number
Enable
Circuit Breaker
Package
MIC2040-1BMM
Active-High
10-Pin MSOP
MIC2040-2BMM
Active-Low
10-Pin MSOP
MIC2041-1BMM
Active-High
X
10-Pin MSOP
MIC2041-2BMM
Active-Low
X
10-Pin MSOP
MIC2040/2041
Micrel
M9999-012004
2
January 2004
Pin Configuration
ILIM
VBIAS
6
5
1
EN
/FAULT
UVLOIN
GND
10 VOUT
VIN
VOUT
VIN
9
8
7
2
3
4
MIC2040/MIC2041
10-Pin MSOP (MM)
Pin Description
Pin Number
Pin Name
Pin Function
1
EN
Switch Enable Input: Gate control pin of the output MOSFET available as an
active high (1) or active low (2) input signal.
2
/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 28ms.
4
GND
Ground Connection: Tie to analog ground.
5
ILIM
Current Limit Set: A resistor, R
SET
, connected to this pin sets the current
limit threshold as CLF/R
SET
, where CLF is the current limit factor specified in
the electrical characteristics table. For the MIC2040/41, the continuous
output current range is 0.25A to 1.5A.
7, 9
VIN
Switch Input Supply: 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.
8, 10
VOUT
Switch Output: The source of the output MOSFET. These pins must be
externally connected together.
6
VBIAS
Bias Supply Input: This input pin supplies bias to operate the switch with
range from 1.6V to 5.5V. When switching voltage (V
IN
) is between 1.6V to
5.5V and the use of a single supply is desired, connect VBIAS to VIN
externally.
3
UVLOIN
Undervoltage Lockout Adjust Input: With this pin left open, the UVLO
threshold is internally set to 1.45V. When the switching voltage (V
IN
) is at or
below 1.6V, connecting an external resistive divider to this input will lower
the UVLO threshold. The total resistance must be less than 200k. See
"Applications Information"
for further detail.
January 2004
3
M9999-012004
MIC2040/2041
Micrel
Absolute Maximum Ratings
(1)
V
IN
and V
BIAS ..................................................................................
6V
/FAULT, PWRGD Output Voltage ................................... 6V
/FAULT, PWRGD Output Current .............................. 25mA
Junction Temperature Range ................... Internally Limited
ESD Rating
(3)
Human Body Model ................................................... 2kV
Machine Model ........................................................ 200V
Operating Ratings
(2)
Supply Voltage
V
IN
............................................................... 0.8V to 5.5V
V
BIAS
........................................................... 1.6V to 5.5V
Continuous Output Current ........................... 0.25A to 1.5A
Ambient Temperature (T
A
) ........................... 40C to 85C
Package Thermal Resistance (R
(J-A)
)
MSOP ................................................................ 160C/W
Electrical Characteristics
(4)
V
IN
= V
BIAS
= 5V. T
A
= 25C unless specified otherwise. Bold indicates 40C to +85C.
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
IN
Switch Input Voltage
V
IN
V
BIAS
0.8
5.5
V
V
BIAS
Bias Supply Voltage
1.6
5.5
V
I
BIAS
VBIAS Supply Current - Switch OFF
No load
0.1
5
A
VBIAS Supply Current - Switch ON
No load
250
400
A
Note 5
V
EN
Enable Input Voltage
V
IL(max)
2.4
1.5
V
V
IH(min)
3.5
2.5
V
V
ENHYS
Enable Input Threshold Hysteresis
100
mV
I
EN
Enable Input Current
V
EN
= 0V to 5.5V
1
.01
1
A
R
DS(ON)
Switch Resistance
V
IN
= V
BIAS
= 3V, 5V
50
75
m
I
OUT
= 500mA
I
LEAK
Output Leakage Current
Output off
10
A
CLF
Current Limit Factor
(6)
V
IN
= 3V, 5V; 0.5V V
OUT
< 0.5V
IN
280
340
400
A
0.25A I
OUT
1.5A
V
LATCH
Output Reset Threshold
V
IN
= 0.8V to 5.5V
V
IN
.0.2
V
V
OUT
rising (MIC2041)
I
LATCH
Latched Output Off Current
Output latched off (MIC2041)
1
3
5
mA
V
OL
Output low voltage
I
OL
(/FAULT) = 15mA
0.4
V
(/FAULT)
I
OFF
/FAULT Off Current
V
FAULT
= 5V
1
A
V
UV
Undervoltage Lockout Threshold
V
IN
rising
1.30
1.45
1.58
V
V
IN
falling
1.20
1.35
1.50
V
V
UVHYS
Undervoltage Lockout
100
mV
Threshold Hysteresis
V
UVINTH
UVLO Adjust Pin Threshold Voltage
V
IN
rising
200
220
240
mV
V
IN
falling
180
200
220
mV
V
UVINHYS
UVLO Adjust Pin Threshold Hysteresis
20
mV
Overtemperature Threshold
T
J
increasing
140
C
T
J
decreasing
120
C
Notes:
1.
Exceeding the absolute maximum rating may damage the device.
2.
The device is not guaranteed to function outside its operating rating.
3.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
4.
Specification for packaged product only.
5.
OFF is V
EN
< 1.0V for MIC2040/MIC20411 and V
EN
> 4.0V for MIC2040/MIC2041 2. ON is V
EN
> 4.0V for MIC2040/MIC20411 and
V
EN
< 1.0V for MIC2040/MIC2041 2.
6.
The current limit is determined as follows: I
LIM
= CLF/R
SET
.
MIC2040/2041
Micrel
M9999-012004
4
January 2004
Electrical Characteristics
(7)
Symbol
Parameter
Condition
Min
Typ
Max
Units
t
FLAG
Flag Response Delay
V
IN
= V
BIAS
= 3V, 5V
21
28
35
ms
t
ON
Output Turn-on Delay,
R
LOAD
= 10, C
LOAD
= 1F
400
600
800
s
t
R
Output turn-on Rise Time
R
LOAD
= 10, C
LOAD
= 1F
0.5
1
1.5
ms
t
OFF
Output Turn-off Delay
R
LOAD
= 10, C
LOAD
= 1F
1
5
s
t
F
Output Turn-off Fall Time
R
LOAD
= 10, C
LOAD
= 1F
24
s
Note:
7.
Specification for packaged product only.
Timing Diagrams
50%
(a) MIC2040/41-1
(b) MIC2040/41-2
10%
90%
0
V
EN
t
ON
t
OFF
0
V
OUT
50%
10%
90%
0
V
EN
t
ON
t
OFF
0
V
OUT
Figure 1. Turn-On/Turn-Off Delay
0
V
EN
I
LIMIT
0
V
OUT
0
I
OUT
0
/FAULT
t
FLAG
V
IN
0.2V
Increase the load
Figure 2. Overcurrent Fault Response -- MIC2040-2
January 2004
5
M9999-012004
MIC2040/2041
Micrel
Test Circuit
7, 9
6
1
2
3
8,10
5
R
SET
C1
0.1mF
4
MIC2040/41-xBM
VBIAS
VIN
EN
/FAULT
UVLOIN
VOUT
ILIM
GND
R2
20kW
R1
20kW
C
LOAD
V
OUT
C2
0.1mF
V
IN
V
DD
R3
75kW
R4
68kW
MIC2040/2041
Micrel
M9999-012004
6
January 2004
Typical Characteristics
100
150
200
250
300
350
400
450
500
-40 -20
0
20
40
60
80 100
SUPPLY CURRENT (
A)
TEMPERATURE (C)
Supply Current
vs. Temperature
V
IN
= V
BIAS
= 1.6V
V
IN
= V
BIAS
= 5.5V
V
IN
= V
BIAS
= 3V
0
0.5
1
1.5
2
2.5
3
3.5
-40 -20
0
20
40
60
80 100
V
EN
(V)
TEMPERATURE (C)
Enable Input Threshold
(Falling)
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
0
0.5
1
1.5
2
2.5
3
3.5
-40 -20
0
20
40
60
80 100
V
EN
(V)
TEMPERATURE (C)
Enable Input Threshold
(Rising)
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
0
300
600
900
1200
1500
1800
2100
2400
2700
3000
-40 -20
0
20
40
60
80 100
OUTPUT LEAKAGE (nA)
TEMPERATURE (C)
Output Leakage Current
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
0
10
20
30
40
50
60
70
80
-40 -20
0
20
40
60
80 100
RDS(m
)
TEMPERATURE (C)
ON Resistance (R
DS(ON)
)
vs. Temperature
V
IN
= V
BIAS
= 5V
V
IN
= V
BIAS
= 3V
V
IN
= V
BIAS
= 1.6V
300
310
320
330
340
350
360
370
380
390
400
-40 -20
0
20
40
60
80 100
CURRENT LIMIT FACTOR (V)
TEMPERATURE (C)
Current Limit Factor
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
R
SET
= 0.4A
300
310
320
330
340
350
360
370
380
390
400
-40 -20
0
20
40
60
80 100
CURRENT LIMIT FACTOR (V)
TEMPERATURE (C)
Current Limit Factor
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
R
SET
= 0.85A
300
310
320
330
340
350
360
370
380
390
400
-40 -20
0
20
40
60
80 100
CURRENT LIMIT FACTOR (V)
TEMPERATURE (C)
Current Limit Factor
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
R
SET
= 1.5A
0
50
100
150
200
250
300
-40 -20
0
20
40
60
80 100
V
OL
(mV)
TEMPERATURE (C)
Output Low Voltage
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
I
OL
(/FAULT) = 15mA
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
-40 -20
0
20
40
60
80 100
UVLO (V)
TEMPERATURE (C)
UVLO Threshold
vs. Temperature
UVLO+
UVLO
180
185
190
195
200
205
210
215
220
225
230
235
240
-40 -20
0
20
40
60
80 100
UVLO (V)
TEMPERATURE (C)
UVLO Adjust PinThreshold
vs. Temperature
UVLO+
UVLO
20
25
30
35
40
45
50
-40 -20
0
20
40
60
80 100
T
FLAG
(ms)
TEMPERATURE (C)
Flag Response Delay
vs. Temperature
T
FLAG
= 3V
T
FLAG
= 5V
January 2004
7
M9999-012004
MIC2040/2041
Micrel
Typical Characteristics (continued)
350
400
450
500
550
600
650
700
750
800
-40 -20
0
20
40
60
80 100
TURN ON DELAY (
s)
TEMPERATURE (C)
Turn On Delay
vs. Temperature
V
IN
= V
BIAS
= 5.5V
V
IN
= V
BIAS
= 3V
V
IN
= V
BIAS
= 1.6V
350
400
450
500
550
600
650
700
750
800
-40 -20
0
20
40
60
80 100
T
ON
(s)
TEMPERATURE (C)
Output Rise Time
vs. Temperature
V
IN
= V
BIAS
= 5.5V
V
IN
= V
BIAS
= 3V
V
IN
= V
BIAS
= 1.6V
MIC2040/2041
Micrel
M9999-012004
8
January 2004
Functional Diagram
MIC2040/41
Bandgap
Reference
OSC
UVLO
5.3x
1x
V
REF
= 230mV
Current
Limit
Replica
Amp
+
+
V
IN
ILIM
5
VOUT
8,10
VBIAS
6
VIN
7,9
/FAULT
2
GND
4
+
Gate
Control
UVLOIN
3
EN
1
Open
Load
Detect
I
LIM
Delay
(28ms)
Error
Flag
Logic
Power-On
Reset
Input
Logic
Latch
(MIC2041)
Charge
Pump
Thermal
Shutdown
Power-Off
Reset
January 2004
9
M9999-012004
MIC2040/2041
Micrel
Functional Characteristics
Turn-On Response
TIME (1ms/div.)
I
OUT
(1A/div
.)
EN
(5V/div
.)
V
OUT
(2V/div
.)
V
IN
= V
BIAS
=5V
R
LOAD
= 5
C
LOAD
= 47
F
Turn-Off Response
TIME (500s/div.)
I
OUT
(1A/div
.)
EN
(5V/div
.)
V
OUT
(2V/div
.)
V
IN
= V
BIAS
= 5V
R
LOAD
= 5
C
LOAD
= 47F
Latched Output - MIC2041
TIME (5ms/div.)
I
OUT
(1A/div
.)
EN
(5V/div
.)
V
OUT
(5V/div
.)
/F
AUL
T
(5V/div
.)
V
IN
= V
BIAS
= 5V
R
LOAD
= 35
C
LOAD
= 57
F
Latched Output Reset - MIC2041
TIME (50ms/div.)
EN
(5V/div
.)
V
OUT
(2V/div
.)
/F
AUL
T
(5V/div
.)
V
IN
= V
BIAS
= 5V
R
LOAD
= 35
C
LOAD
= 57
F
Current-Limit Response
TIME (5ms/div.)
I
OUT
(1A/div
.)
EN
(5V/div
.)
V
OUT
(5V/div
.)
/F
AUL
T
(5V/div
.)
V
IN
= V
BIAS
= 5V
R
LOAD
= 3.5
C
LOAD
= 47
F
UVLO Response
TIME (10ms/div.)
I
OUT
(500mA/div
.)
V
IN
(1V/div
.)
V
OUT
(1V/div
.)
V
EN
ramps 0 to 1.6V
R
LOAD
= 1.6
C
LOAD
= 47
F
MIC2040/2041
Micrel
M9999-012004
10
January 2004
Thermal Shutdown Response
TIME (100ms/div.)
I
OUT
(1A/div
.)
EN
(5V/div
.)
V
OUT
(5V/div
.)
/F
AUL
T
(5V/div
.)
January 2004
11
M9999-012004
MIC2040/2041
Micrel
Functional Description
The MIC2040 and MIC2041 are high-side N-Channel switches
equipped with programmable current limit up to 1.5A for use
in general purpose power distribution applications. The
switches, available with active-high or active-low enable
inputs, operate down to 0.8V and provide 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 MIC2040/41 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, VIN, and prevents the output
MOSFET from turning on until VIN 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 MIC2040/41 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 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 MIC2040/41 will limit from 0.25A to 1.5A with a set
point accuracy of 18%. In programming the nominal current
limit, the value of R
SET
is determined using the following
equation:
R
CLF
I
340A
I
SET
LIM
LIM
=
=
(
)
(1)
And given the 18% tolerance of the current limit factor (CLF),
the external resistor is bound by:
187 R
SET
1.6k
(2)
The graph below (Figure 3) displays the current limit factor
characteristic over the full temperature and voltage range
indicated on the graph. This curve 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
IN
= V
BIAS
= 3.0V and a nominal 1A current limit (R
SET
= 340), the low and high current limit settings for the
MIC2040/41 would be approximately 0.82A and 1.18A, re-
spectively, as shown on the graph using the 340 reference.
The MIC2041 is equipped with an internal circuit breaker for
overcurrent protection. During an overcurrent event which
exceeds the flag delay, the /FAULT output is asserted and the
MIC2041 latches the output off. Once the overcurrent load is
removed, the output automatically resets.
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
150
300
450
600
750
900
1050
1200
1350
1500
I
LIM
(A)
R
SET
()
Current Limit vs. R
SET
CLF (LO)
V
IN
= 1.6V to 5V
40C to +85C
CLF (HI)
Figure 3. Current Limit Factor
MIC2040/2041
Micrel
M9999-012004
12
January 2004
/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
MIC2040/41. In the case where an overcurrent condition
occurs, /FAULT will assert only after the flag delay time has
elapsed, typically 28ms. This ensures that /FAULT is as-
serted only upon valid overcurrent conditions and that nui-
sance error reporting is prevented.
Thermal Shutdown
For the MIC2040, 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 140C. The
MIC2040 automatically resets its output and resumes supply-
ing current to the load when the die temperature drops to
120C. If the fault is still present, the MIC2040 will quickly
reheat 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 (MIC2041)
The MIC2041 is designed to shut off all power to the load
when a fault condition occurs, just as a circuit breaker would
do. A fault condition is deemed to be anytime the output
current exceeds the current limit for more than the flag delay
period, nominally 28ms. 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 MIC2041 will again shut off all power to
the load after 28ms. Once the fault has been removed, then
normal operation will resume.
Open Load Detection
The MIC2041 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
MIC2041 latches off.
January 2004
13
M9999-012004
MIC2040/2041
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 0.1F to 0.47F 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 4.7F to 15F. 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 MIC2040 die exceeds the overtemperature thresh-
old of approximately 140C, the device can enter into a
thermal shutdown mode if the die temperature falls below
120C and then rises above 140C in a continuous cycle.
With the V
OUT
and /FAULT outputs cycling on and off, the
MIC2040 will reset the /FAULT while in an overtemperature
fault condition if the output voltage is allowed to swing below
ground. The inductance present at the output must be neu-
tralized 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
(<1 ft., 16 - 20 gauge wire), a minimum output capacitance of
22F is strongly recommended and should be placed close
to the V
OUT
pin of the MIC2040. For applications that use
more than a foot of cable, an additional 10F/ft. is recom-
mended.
Reverse Current Block
The MIC2040/41 provides reverse current flow block through
the output MOSFET if the voltage at VOUT is greater than VIN
when the device is disabled. The VBIAS supply has a limited
reverse current flow if the voltage at VOUT is pulled above
VBIAS when the device is disabled. 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.
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 operating voltages. An external resistive divider net-
work connected 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.
V
0.23V
1
R2
R3
UVTH
=
+
(3)
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 0.1F to 1.0F 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
MIC2040/41.
7,9
8
1
3
5
8,10
2
R
SET
220
C1
0.1
F
10
MIC2040-1BM
VBIAS
VIN
EN
/FAULT
UVLOIN
VOUT
ILIM
GND
R1
47k
R4
75k
1%
R5
36.5k
1%
C
LOAD
22
F
V
OUT
0.8V @1.25A
R6
47k
Digital
Output
Signal
C3
10
F
C2
0.1
F
V
IN
0.8V
V
DD
2.5V
R2
95.3k
1%
R3
59k
1%
Note:
Both V
IN
pins (7, 9) must be externally tied together.
Both V
OUT
pins (8, 10) must be externally tied together.
Undervoltage Lockout = 0.6V.
Figure 4. Lower UVLO Setting
MIC2040/2041
Micrel
M9999-012004
14
January 2004
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:
P
D
= R
DS(on)
(I
OUT
)
2
(4)
To relate this to junction temperature, the following equation
can be used:
T
J
= P
D
R
(J-A)
+ T
A
(5)
where T
J
= junction temperature, T
A
= ambient temperature
and R
(J-A)
is the thermal resistance of the package.
Printed Circuit Board Hot-Plug
The MIC2040/41 are ideal inrush current limiting power
switches suitable for hot plug applications. Due to the inte-
grated charge pump, the MIC2040/41 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.
Bus-Powered Hub (USB)
Figure 5 illustrates a bus-powered hub application where the
MIC2040 provides ganged power switching to multiple down-
stream ports. A low-cost MIC5203 (SOT-143) or MIC5207
(TO-92) 3.3V low-dropout (LDO) regulator provides power
from the bus to the USB controller.
PCB Layout Recommendations
The MIC2040 and MIC2041 have very low on-resistance,
typically 50m, and the switches can provide up to 1.5A of
continuous output current. Under maximum load, the power
consumed by the devices may cause the devices to heat up
considerably. The following list contains some useful sug-
gestions for PCB layout design of the MIC2040/41 in order to
prevent the die from overheating under normal operating
conditions.
7, 9
6
1
2
5
8,10
3
R
SET
220
Note:
BothV
IN
pins (7, 9) must be externally tied together.
BothV
OUT
pins (8, 10) must be externally tied together.
I
LIMIT
= 1.5A.
C2
0.1F
3.3V USB
Controller
MIC5203-3.3
ON/OFF
OC
IN
D+
D-
GND
4
MIC2040-1BM
VBIAS
VIN
EN
/FAULT
ILIM
VOUT
UVLOIN
GND
LDO
Regulator
R2
20k
R1
20k
C
LOAD
10F
(OPEN)
V
OUT
5V@ 1A
C1
0.1F
C
LOAD
10F
C
LOAD
10F
Downstream port
(100mA max.)
Downstream port
(100mA max.)
Downstream port
(100mA max.)
GND
OUT
IN
C4
1F
C3
4.7F
VBUS
D+
D-
GND
Figure 5. Multi-Port Bus-Powered Hub
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 MIC2040/41 IC for heat distribution.
3. Tie the common power pins (V
IN
= pins 7 and 9
and V
OUT
= pins 8 and 10) together in a manner
such that the traces entering and leaving the
device have a uniform width sufficient for the
application's current requirements plus added
margin (25% minimum recommended).
Ex: For 1A maximum current, design traces for
1.25A capability.
4. For PCB trace width calculations, there are
numerous calculator programs available on the
internet and elsewhere. As a general rule of
thumb, 15-20 mils for every 1A of current when
using 1oz. copper. However, the trace width
calculators often take into account maximum
temperature increase constraints, as well as
layer arrangement, in determining the PCB trace
widths.
January 2004
15
M9999-012004
MIC2040/2041
Micrel
Package Information
I
Rev. 00
10-Pin MSOP (MM)
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.
2003 Micrel, Incorporated.
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