January 2005 1 M0512-112603
MIC2042/2043 Micrel
MIC2042/2043
Single Channel, High Current, Low Voltage,
Protected Power Distribution Switch
General Description
The MIC2042 and MIC2043 are high-side MOSFET switches
optimized for general purpose power distribution applications
which 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, for tighter control over inrush current during
start-up, the output slew-rate may be adjusted by an external
capacitor.
The MIC2043 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.
All support documentation can be found on Micrel’s web
site at www.micrel.com.
Typical Application
Features
• 60mΩ max. on-resistance
•0.8V to 5.5V operating range
•Adjustable current limit
•Power-Good detection
•Up to 3A continuous output current
•Short-circuit protection with thermal shutdown
•Adjustable slew-rate control
•Circuit breaker mode (MIC2043)
•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
•Hot swap board insertions
•RAID controllers
•USB hosts
•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
8, 12
7
2
3
6
9
13
10,11,14
1
4
R
SET
200ΩNote:
All V
IN
pins (8, 12) must be externally tied together.
All V
OUT
pins (10, 11, 14) must be externally tied together.
I
LIMIT
≅ 2A.
Output Power-Good = 3.0V.
*C4 is optional. See "Applications Information."
C4*
0.022µF
C1
0.1µF
Logic
Controller
ON/OFF
OVERCURRENT
IN
5
MIC2042-1BTS
MIC39100-2.5BS
VBIAS
VIN
EN
/FAULT
ILIM
SLEW 2.5V
VOUT
PGREF
PWRGD
UVLOIN
GND
+3.3V
Power
Supply
R1
20kΩ
R4
20kΩ
R2
294kΩ
1%
R3
24.3kΩ
1%
EN
IN
GND
OUT
CLOAD
33µF
(OPEN)
VOUT
3.3V@ 1.5A
OUT1 OUT2
C2
0.1µF
C3
4.7µF
MIC2042/2043 Micrel
M0512-112603 2January 2005
Pin Configuration
1EN
/FAULT
GND
ILIM
8 VOUT
VIN
VOUT
VIN
7
6
5
2
3
4
8-Pin SOP (M)
Ordering Information
Part Number
Standard Pb-Free Enable Circuit Breaker VBIAS VIN Range Package
MIC2042-1BM MIC2042-1YM Active High 1.6V to 5.5V 8-pin SOP
MIC2042-2BM MIC2042-2YM Active Low 1.6V to 5.5V 8-pin SOP
MIC2043-1BM MIC2043-1YM Active High X 1.6V to 5.5V 8-pin SOP
MIC2043-2BM MIC2043-2YM Active Low X 1.6V to 5.5V 8-pin SOP
MIC2042-1BTS MIC2042-1YTS Active High X 0.8V to 5.5V 14-pin TSSOP
MIC2042-2BTS MIC2042-2YTS Active Low X 0.8V to 5.5V 14-pin TSSOP
MIC2043-1BTS MIC2043-1YTS Active High X X 0.8V to 5.5V 14-pin TSSOP
MIC2043-2BTS MIC2043-2YTS Active Low X X 0.8V to 5.5V 14-pin TSSOP
1PWRGD
EN
/FAULT
UVLOIN
GND
ILIM
VBIAS
14 VOUT
PGREF
VIN
VOUT
VOUT
SLEW
VIN
13
12
11
10
9
8
2
3
4
5
6
7
14-Pin TSSOP (TS)
January 2005 3 M0512-112603
MIC2042/2043 Micrel
Pin Description
Pin Number Pin Number Pin Name Pin Function
8-Pin SOP 14-Pin TSSOP
12 EN Switch Enable Input: Gate control pin of the output MOSFET available as an
active high (–1) or active low (–2) input signal.
23/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.
35 GND Ground Connection: Tie to analog ground.
N/A 9 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 28ms in order to avoid nuisance tripping of the
/FAULT output since VOUT must be “fully on” (i.e., within 200mV of the voltage
at the input) before the /FAULT signal delay elapses. The capacitor requires a
16V rating, or greater, 25V is recommended. See “Applications Information,”
“Output Slew-Rate Adjustment” for further detail.
46 ILIM Current Limit Set: A resistor, RSET, connected to this pin sets the current
limit threshold as CLF/RSET, where CLF is the current limit factor specified in
the “Electrical Characteristics” table. For the MIC2042/43, the continuous
output current range is 0.5A to 3A.
5,7 8,12 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
to achieve rated performance.
6,8 10,11,14 VOUT Switch Output: The source of the output MOSFET. These pins must be
externally connected together to achieve rated performance.
N/A 7 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 (VIN) is between 1.6V to 5.5V and the use of a single supply is desired,
connect VBIAS to VIN externally.
N/A 13 PGREF Power-Good Threshold (Input): Analog reference used to specify the
PWRGD threshold. When the voltage at this pin exceeds its threshold, VTH,
PWRGD is asserted high. An external resistive divider network is used to
determine the output voltage level at which VTH is exceeded. See
“Functional Description” for further detail. When the PWRGD signal is not
utilized, this input should be tied to VOUT.
N/A 1 PWRGD Power-Good Output: Active high, open-drain. This pin asserts high when the
voltage at PGREF exceeds its threshold.
N/A 4 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 below
1.6V, connecting
an external resistive divider to this input will lower the
UVLO threshold. The total resistance of the divider must be less than
200kΩ. See “Applications Information” for further detail.
MIC2042/2043 Micrel
M0512-112603 4January 2005
Electrical Characteristics(4)
VIN = VBIAS = 5V; TA = 25°C unless specified otherwise. Bold indicates –40°C to +85°C.
Symbol Parameter Condition Min Typ Max Units
VIN Switch Input Voltage VIN ≤ VBIAS 14-pin TSSOP 0.8 5.5 V
8-pin SOP 1.6 5.5 V
VBIAS Bias Supply Voltage (14-pin TSSOP) 1.6 5.5 V
IBIAS VBIAS Supply Current - Switch OFF No load 0.1 5µA
VBIAS Supply Current - Switch ON No load 300 400 µA
Note 5
VEN Enable Input Voltage VIL(max) 2.4 1.5 V
VIH(min) 3.5 2.5 V
VENHYST Enable Input Threshold Hysteresis 100 mV
IEN Enable Input Current VEN = 0V to 5.5V –1 .01 1µA
RDS(ON) Switch Resistance VIN = VBIAS = 3V, 5V 40 60 mΩ
IOUT = 500mA
ILEAK Output Leakage Current Output off 10 µA
CLF Current Limit Factor(2) VIN = 5V, 0.5V ≤ VOUT < 0.5VIN 310 395 485 A×Ω
0.5A ≤ IOUT ≤ 3A
VIN = 3V, 0.5V ≤ VOUT < 0.5VIN 320 385 450 A×Ω
0.5A ≤ IOUT ≤ 3A
VTH PGREF and UVLOIN Threshold VIN = VBIAS = 1.6V to 5.5V 205 225 245 mV
(14-pin TSSOP)
VLATCH Output Reset Threshold VIN = 0.8V to 5.5V VIN–.0.2 V
VOUT rising (MIC2043)
ILATCH Latched Output Off Current Output latched off (MIC2043) 1 3 5 mA
VOL Output Low Voltage IOL (/FAULT) = 15mA 0.4 V
(/FAULT, PWRGD) IOL (PWRGD) = 5mA
IOFF /FAULT, PWRGD Off Current VFAULT = VPWRGD = 5V 1µA
VUV Undervoltage Lockout Threshold VIN rising 1.30 1.45 1.58 V
VIN falling 1.20 1.35 1.50 V
VUVHYST Undervoltage Lockout 100 mV
Threshold Hysteresis
VUVINTH UVLO Adjust Pin Threshold Voltage VIN rising 205 225 245 mV
VIN falling 185 205 225 mV
VUVINHYST UVLO Adjust Pin Threshold Hysteresis 20 mV
Overtemperature Threshold TJ increasing 140 °C
TJ decreasing 120 °C
Absolute Maximum Ratings(1)
Supply Voltage
VIN and VBIAS ............................................................................. 6V
/FAULT, PWRGD Output Voltage ................................... 6V
/FAULT, PWRGD Output Current .............................. 25mA
Junction Temperature (TJ)...................... Internally Limited
ESD Rating(3)
Human Body Model ................................................... 3kV
Machine Model ........................................................ 200V
Operating Ratings(2)
Supply Voltage
VIN ............................................................... 0.8V to 5.5V
VBIAS ........................................................... 1.6V to 5.5V
Continuous Output Current ................................ 0.5A to 3A
Ambient Temperature (TA) ........................... –40°C to 85°C
Package Thermal Resistance
SOP (θJA) .......................................................... 160°C/W
TSSOP (θJA) ....................................................... 85°C/W
January 2005 5 M0512-112603
MIC2042/2043 Micrel
Symbol Parameter Condition Min Typ Max Units
tFLAG Flag Response Delay VIN = VBIAS = 3V, 5V 21 28 35 ms
tON Output Turn-on Delay RLOAD = 10Ω, CLOAD = 1µF600 800 1000 µs
tROutput Turn-on Rise Time RLOAD = 10Ω, CLOAD = 1µF11.5 2 ms
tOFF Output Turn-off Delay RLOAD = 10Ω, CLOAD = 1µF15µs
tFOutput Turn-off Fall Time RLOAD = 10Ω, CLOAD = 1µF24µs
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 VEN < 1.0V for MIC2042/MIC2043-1 and VEN > 4.0V for MIC2042/MIC2043-2. ON is VEN > 4.0V for MIC2042/MIC2043-1 and VEN < 1.0V for
MIC2042/MIC2043-2.
6. The current limit is determined as follows: ILIM = CLF/RSET.
Timing Diagrams
50%
(a) MIC2042/43-1
(b) MIC2042/43-2
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
VEN
ILIMIT
0
VOUT
0
IOUT
0
/FAULT
tFLAG
VIN 0.2V
Increase the load
Figure 2. Overcurrent Fault Response — MIC2042-2
MIC2042/2043 Micrel
M0512-112603 6January 2005
Test Circuit
8, 12
7
2
3
4
9
13
10,11,14
1
6
RSET
200
W
*CSLEW uses multiple values
(See specific response plots)
*CSLEW
C1
0.1
m
F
5
MIC2042/43-xBTS
VBIAS
VIN
EN
/FAULT
UVLOIN
SLEW
VOUT
PGREF
PWRGD
ILIM
GND
R2
20k
W
R1
20k
W
R5
260k
W
R6
24k
W
CLOAD
47
m
F
VOUT
ILOAD
R7
20k
W
C3
10
m
F
C2
0.1
m
F
VIN
VDD
R3
75k
W
R4
68k
W
January 2005 7 M0512-112603
MIC2042/2043 Micrel
Typical Characteristics
100
150
200
250
300
350
400
450
500
-40 -20 0 20 40 60 80 100
SUPPLY CURRENT (µA)
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
VBIAS = 5.5V
VBIAS = 3V
VBIAS = 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
VBIAS = 5.5V
VBIAS = 3V
VBIAS = 1.6V
0
100
200
300
400
500
600
-40 -20 0 20 40 60 80 100
OUTPUT LEAKAGE (nA)
TEMPERATURE (°C)
Output Leakage Current
vs. Temperature
VBIAS = 5.5V
VBIAS = 3V
VBIAS = 1.6V
210
215
220
225
230
-40 -20 0 20 40 60 80 100
V TH (mV)
TEMPERATURE (°C)
Power-Good Reference
Threshold
vs. Temperature
VTH @ 1.6V to 5.5V
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–
200
205
210
215
220
225
230
235
240
245
250
-40 -20 0 20 40 60 80 100
UVLO (V)
TEMPERATURE (°C)
UVLO Adjust PinThreshold
vs. Temperature
UVLO+
UVLO–
0
10
20
30
40
50
60
70
80
-40 -20 0 20 40 60 80 100
RDS(ON)
TEMPERATURE (°C)
On Resistance
vs. Temperature
VIN =V
BIAS = 5V
VIN =V
BIAS = 3V
VIN =V
BIAS = 1.6V
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
TFLAG = 3V
TFLAG = 5V
500
550
600
650
700
750
800
850
900
-40 -20 0 20 40 60 80 100
TURN ON DELAY (µs)
TEMPERATURE (°C)
Turn-On Delay
vs. Temperature
VIN =V
BIAS = 5.5V
VIN =V
BIAS = 3V
VIN =V
BIAS = 1.6V
0
2
4
6
8
10
12
14
16
18
20
2 2.5 3 3.5 4 4.5 5 5.5 6
I
R
(mA)
V
OUT
(V)
V
BIAS
Reverse Current Flow
vs. Output Volta
g
e
V
IN
= GND
V
BIAS
= 1.6V
0
5
10
15
20
25
-40 -20 0 20 40 60 80 100
SLEW VOLTAGE (V)
TEMPERATURE (°C)
Slew Voltage
vs. Temperature
V
IN
=V
BIAS
= 5V
V
IN
=V
BIAS
= 3V
V
IN
=V
BIAS
= 1.6V
MIC2042/2043 Micrel
M0512-112603 8January 2005
Functional Characteristics
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January 2005 9 M0512-112603
MIC2042/2043 Micrel
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MIC2042/2043 Micrel
M0512-112603 10 January 2005
Functional Diagram
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MIC2042/43 Block Diagram
January 2005 11 M0512-112603
MIC2042/2043 Micrel
Functional Description
The MIC2042 and MIC2043 are high-side N-Channel switches
equipped with programmable current limit up to 3A 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 connected 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 MIC2042/43 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” section.
Programmable Current Limit
The MIC2042/43 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 (RSET) 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 RSET,
and the MIC2042/43 will limit from 0.5A to 3A with a set point
accuracy of ±22%. In programming the nominal current limit,
the value of RSET is determined using the following equation:
RCLF
I
390A
I
SET LIMIT LIMIT
== ×Ω
()
(1)
And given the ±22% tolerance of the current limit factor (CLF),
the external resistor is bound by:
103Ω ≤ RSET ≤ 970Ω (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
VIN = VBIAS = 3.0V and a nominal 2A current limit
(RSET = 192Ω), the low and high current limit settings for the
MIC2042/43 would be 1.66A and 2.34A, respectively, as
shown on the 3V graph using the 192Ω reference point.
When current limiting occurs, the MIC2042 and MIC2043
respond differently. Upon first reaching the limiting current
both devices restrict current flow, allowing the load voltage to
drop below VIN. If the VIN-to-VOUT differential voltage ex-
ceeds 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 28ms, then the /FAULT output
asserts low. At this point, the MIC2042 will continue to supply
current to the load at the limiting value (ILIMIT), whereas the
MIC2043 will latch off its output.
0
0.5
1
1.5
2
2.5
3
3.5
4
0 120 240 360 480 600 720 840 960
I LIM (A)
R SET (Ω)
Current Limit
vs. R
SET
–40°C to +85°C
V
IN
=V
BIAS
= 5V
CLF (LO)
CLF (HI)
0
0.5
1
1.5
2
2.5
3
3.5
4
0 120 240 360 480 600 720 840 960
I
LIM
(A)
R
SET
(Ω)
Current Limit
vs. RSET
–40°C to +85°C
VIN =V
BIAS = 3V
CLF (LO)
CLF (HI)
0
0.5
1
1.5
2
2.5
3
3.5
4
0 120 240 360 480 600 720 840 960
I
LIM
(A)
R
SET
(Ω)
Current Limit
vs. RSET
–40°C to +85°C
VIN =V
BIAS = 1.6V
CLF (LO)
CLF (HI)
Figure 3. Current Limit Factor
MIC2042/2043 Micrel
M0512-112603 12 January 2005
/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
MIC2042/43. 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 MIC2042, 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°C. The
MIC2042 automatically resets its output and resumes supply-
ing current to the load when the die temperature drops to
120°C. If the fault is still present, the MIC2042 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 (MIC2043)
The MIC2043 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 MIC2043 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 MIC2043 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
MIC2043 latches off.
Power-Good Detection
The MIC2042/43 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 (VTH), 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:
VV1
R2
R3
OUT(GOOD) TH
=×+
(3)
In substituting the resistor values of the circuit and the typical
PGREF threshold, the resulting VOUT(GOOD) is calculated as
3.0V for this 3.3V switching application.
Slew
The MIC2042/43’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.
January 2005 13 M0512-112603
MIC2042/2043 Micrel
Applications Information
Input and Output
Supply Bypass Filtering
The need for input supply bypass is necessary due to several
factors, most notably the input/output inductance along the
power path, operating current and current limit, and output
capacitance. A 0.1µF to 0.47µF 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 positioned
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 applica-
tion and design. A good starting point is a capacitor between
4.7µF to 15µF. Without these bypass capacitors, an extreme
overload condition such as a short circuit, or a large capaci-
tive 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 MIC2042 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 the VOUT and /FAULT outputs cycling on and off, the
MIC2042 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
power cable (≤ 1ft., 16 to 20 gauge wire), a minimum output
capacitance of 22µF is strongly recommended and should be
placed close to the VOUT pin of the MIC2042. For applica-
tions that use more than a foot of cable, an additional
10µF/ft. is recommended.
Reverse Current Block
The MIC2042/43 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 pin has a
limited reverse current flow if the voltage at VOUT is pulled
above VBIAS when the device is disabled. A graph of the
VBIAS reverse current flow is shown in the “Functional Char-
acteristics” plots. 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 MIC2042/43 can be slowed down
by the capacitor (16V rating, minimum; 25V suggested)
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” plots.
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 28ms 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 MIC2043, 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 func-
tion 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
200kΩ. 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
=×+
(4)
In substituting the resistor values from Figure 4, the resulting
UVLO threshold (VUVTH) is calculated as 0.6V for this 0.8V
switching application. When using the UVLOIN pin to set a
new UVLO threshold, an optional 0.1µF to 1.0µF 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
MIC2042/43.
Conditions: VIN = VBIAS = 5V/3V; CLOAD = 47µF; ILOAD = 1A
CSLEW (µF) Rise Time (ms)
5V 3V
0.01 3 4.75
0.033 10.5 15
0.047 14 21
0.1 32 46
Table 1. Typical Output Rise Time for Various CSLEW
MIC2042/2043 Micrel
M0512-112603 14 January 2005
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:
PD = RDS(ON) × (IOUT)2 (5)
To relate this to junction temperature, the following equation
can be used:
TJ = PD × RθJA + TA (6)
where TJ = junction temperature, TA = ambient temperature
and RθJA is the thermal resistance of the package.
Printed Circuit Board Hot-Plug
The MIC2042/43 are ideal inrush current limiting power
switches suitable for hot-plug applications. Due to the inte-
grated charge pump, the MIC2042/43 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 MIC2042 and MIC2043 have very low on-resistance,
typically 40mΩ, and the switches can provide up to 3A of
continuous output current. Under such heavy loads, the
power consumed by the devices may cause the devices to
8, 12
7
2
4
9
6
13
10,11,14
1
3
R
SET
200
W
C1
0.1
m
F
5
MIC2042-1BTS
VBIAS
VIN
EN
/FAULT
UVLOIN
SLEW
VOUT
PGREF
PWRGD
ILIM
GND
R1
47k
W
R4
75k
W
1%
R5
36.5k
W
1%
C
LOAD
22
m
F
V
OUT
0.8V @1.5A
R7
47k
W
Digital
Output
Signals
C3
10
m
F
C2
0.1
m
F
V
IN
0.8V
V
DD
2.5V
R2
95.3k
W
1%
R3
59k
W
1%
R6
47k
W
Note:
All V
IN
pins (8, 12) must be externally tied together.
All V
OUT
pins (10, 11, 14) must be externally tied together.
Undervoltage Lockout = 0.6V.
Output Power-Good = 0.7V.
Figure 4. Lower UVLO Setting
heat up considerably. The following list contains some useful
suggestions for PCB layout design of the MIC2042/43 in
order to prevent the die from overheating under normal
operating conditions:
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 MIC2042/43 IC for heat distribution.
3. Tie the common power pins (VIN = pins 8 and
12 and VOUT = pins 10, 11, 14 for the 14-pin
TSSOP, VIN = pins 5 and 7 and VOUT = pins 6
and 8 for the 8-pin SOP) 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 2A maximum current, design traces for
2.5A 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 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 2005 15 M0512-112603
MIC2042/2043 Micrel
Package Information
45°
0°–8°
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8) SEATING
PLANE
0.026 (0.65)
MAX)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Pin SOP (M)
1.10 MAX (0.043)
0.15 (0.006)
0.05 (0.002)
1.00 (0.039) REF
0.65 BSC
(0.026) 8°
0°
6.4 BSC (0.252)
5.10 (0.200)
4.90 (0.193)
0.20 (0.008)
0.09 (0.003)
0.70 (0.028)
0.50 (0.020)
DIMENSIONS:
MM (INCH)
4.50 (0.177)
4.30 (0.169)
0.30 (0.012)
0.19 (0.007)
14-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 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 at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
