MIC2043-2BTS [MICREL]
Single Channel, High Current, Low Voltage, Protected Power Distribution Switch; 单通道,高电流,低电压,保护配电开关型号: | MIC2043-2BTS |
厂家: | MICREL SEMICONDUCTOR |
描述: | Single Channel, High Current, Low Voltage, Protected Power Distribution Switch |
文件: | 总15页 (文件大小:832K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
MIC2042/2043
Single Channel, High Current, Low Voltage,
Protected Power Distribution Switch
General Description
Features
TheMIC2042andMIC2043arehigh-sideMOSFETswitches
optimizedforgeneralpurposepowerdistributionapplications
whichrequirecircuitprotection.Thedevicesswitchupto5.5V
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.
• 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
The MIC2043 features a auto-reset circuit breaker mode that
latchestheoutputoffupondetectinganovercurrentcondition
lasting more than 28ms. The output is reset by removing or
reducing the load.
Applications
All support documentation can be found on Micrel’s web
site at www.micrel.com.
• Docking stations
• Notebook PCs
• PDAs
• Hot swap board insertions
• RAID controllers
• USB hosts
• ACPI power distribution
Typical Application
+3.3V
C2
0.1µF
MIC2042-1BTS
VOUT
3.3V@ 1.5A
Power
Supply
7
10,11,14
13
VBIAS
VIN
VOUT
C1
R2
OUT1
OUT2
CLOAD
33µF
0.1µF
294kΩ
1%
8, 12
2
PGREF
C3
4.7µF
R1
20kΩ
R3
24.3kΩ
1%
LogicON/OFF
INController
R4
20kΩ
EN
3
9
6
/FAULT
MIC39100-2.5BS
OVERCURRENT
IN
2.5V
1
4
SLEW PWRGD
EN
OUT
GND
ILIM
UVLOIN
GND
(OPEN)
C4*
0.022µF
RSET
200Ω
5
Note:
All VIN pins (8, 12) must be externally tied together.
All VOUT pins (10, 11, 14) must be externally tied together.
ILIMIT ≅ 2A.
Output Power-Good = 3.0V.
*C4 is optional. See "Applications Information."
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
M0512-112603
January 2005
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MIC2042/2043
Micrel
Ordering Information
Part Number
Standard
Pb-Free
Enable
Circuit Breaker
VBIAS
VIN Range
1.6V to 5.5V
1.6V to 5.5V
1.6V to 5.5V
1.6V to 5.5V
0.8V to 5.5V
0.8V to 5.5V
0.8V to 5.5V
0.8V to 5.5V
Package
8-pin SOP
MIC2042-1BM
MIC2042-2BM
MIC2043-1BM
MIC2043-2BM
MIC2042-1BTS
MIC2042-2BTS
MIC2043-1BTS
MIC2043-2BTS
MIC2042-1YM
MIC2042-2YM
MIC2043-1YM
MIC2043-2YM
MIC2042-1YTS
MIC2042-2YTS
MIC2043-1YTS
MIC2043-2YTS
Active High
Active Low
Active High
Active Low
Active High
Active Low
Active High
Active Low
8-pin SOP
X
X
8-pin SOP
8-pin SOP
X
X
X
X
14-pin TSSOP
14-pin TSSOP
14-pin TSSOP
14-pin TSSOP
X
X
Pin Configuration
PWRGD
1
2
3
4
5
6
7
14 VOUT
13 PGREF
12 VIN
EN
/FAULT
GND
1
2
3
4
8
7
6
5
VOUT
VIN
EN
/FAULT
UVLOIN
GND
VOUT
VIN
11 VOUT
10 VOUT
ILIM
ILIM
9
8
SLEW
VIN
8-Pin SOP (M)
VBIAS
14-Pin TSSOP (TS)
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January 2005
MIC2042/2043
Micrel
Pin Description
Pin Number Pin Number
8-Pin SOP 14-Pin TSSOP
Pin Name
EN
Pin Function
1
2
Switch Enable Input: Gate control pin of the output MOSFET available as an
active high (–1) or active low (–2) input signal.
2
3
/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.
3
5
9
GND
Ground Connection: Tie to analog ground.
N/A
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.
4
6
ILIM
VIN
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
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
7
VOUT
VBIAS
Switch Output: The source of the output MOSFET. These pins must be
externally connected together to achieve rated performance.
N/A
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
N/A
1
4
PWRGD
UVLOIN
Power-Good Output: Active high, open-drain. This pin asserts high when the
voltage at PGREF exceeds its threshold.
Undervoltage Lockout Adjust Input: With this pin left open, the UVLO
threshold is internally set to 1.45V. When the switching voltage (V ) is below
IN
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.
January 2005
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M0512-112603
MIC2042/2043
Micrel
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage
Supply Voltage
V
and V
............................................................................. 6V
V
............................................................... 0.8V to 5.5V
IN
BIAS
IN
/FAULT, PWRGD Output Voltage ...................................6V
/FAULT, PWRGD Output Current ..............................25mA
V
BIAS
........................................................... 1.6V to 5.5V
Continuous Output Current ................................ 0.5A to 3A
Junction Temperature (T ) ...................... Internally Limited
ESD Rating
Ambient Temperature (T ) ........................... –40°C to 85°C
Package Thermal Resistance
J
A
(3)
Human Body Model................................................... 3kV
Machine Model ........................................................200V
SOP (θ ) ..........................................................160°C/W
JA
TSSOP (θ ) .......................................................85°C/W
JA
Electrical Characteristics(4)
VIN = VBIAS = 5V; TA = 25°C unless specified otherwise. Bold indicates –40°C to +85°C.
Symbol
Parameter
Condition
IN ≤ VBIAS
Min
0.8
1.6
1.6
Typ
Max
5.5
Units
VIN
Switch Input Voltage
V
14-pin TSSOP
8-pin SOP
V
V
V
5.5
VBIAS
IBIAS
Bias Supply Voltage
(14-pin TSSOP)
5.5
VBIAS Supply Current - Switch OFF No load
VBIAS Supply Current - Switch ON
Note 5
0.1
300
5
400
µA
µA
No load
VEN
Enable Input Voltage
VIL(max)
VIH(min)
2.4
2.5
100
.01
40
1.5
V
V
3.5
–1
VENHYST
IEN
Enable Input Threshold Hysteresis
Enable Input Current
mV
µA
mΩ
VEN = 0V to 5.5V
1
RDS(ON)
Switch Resistance
VIN = VBIAS = 3V, 5V
IOUT = 500mA
60
ILEAK
CLF
Output Leakage Current
Current Limit Factor(2)
Output off
10
µA
VIN = 5V, 0.5V ≤ VOUT < 0.5VIN
0.5A ≤ IOUT ≤ 3A
310
320
205
395
385
485
A×Ω
VIN = 3V, 0.5V ≤ VOUT < 0.5VIN
450
245
A×Ω
mV
V
0.5A ≤ IOUT ≤ 3A
VTH
PGREF and UVLOIN Threshold
Output Reset Threshold
VIN = VBIAS = 1.6V to 5.5V
(14-pin TSSOP)
225
VLATCH
VIN = 0.8V to 5.5V
VOUT rising (MIC2043)
VIN–.0.2
3
ILATCH
VOL
Latched Output Off Current
Output latched off (MIC2043)
IOL (/FAULT) = 15mA
IOL (PWRGD) = 5mA
VFAULT = VPWRGD = 5V
VIN rising
1
5
mA
V
Output Low Voltage
(/FAULT, PWRGD)
0.4
IOFF
VUV
/FAULT, PWRGD Off Current
1
µA
V
Undervoltage Lockout Threshold
1.30
1.20
1.45
1.35
100
1.58
1.50
VIN falling
V
VUVHYST
VUVINTH
Undervoltage Lockout
Threshold Hysteresis
mV
UVLO Adjust Pin Threshold Voltage VIN rising
VIN falling
205
185
225
205
20
245
225
mV
mV
mV
°C
VUVINHYST
UVLO Adjust Pin Threshold Hysteresis
Overtemperature Threshold
TJ increasing
TJ decreasing
140
120
°C
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January 2005
MIC2042/2043
Micrel
Symbol
tFLAG
tON
Parameter
Condition
Min
21
Typ
28
Max
35
Units
ms
µs
Flag Response Delay
Output Turn-on Delay
Output Turn-on Rise Time
Output Turn-off Delay
Output Turn-off Fall Time
VIN = VBIAS = 3V, 5V
RLOAD = 10Ω, CLOAD = 1µF
RLOAD = 10Ω, CLOAD = 1µF
RLOAD = 10Ω, CLOAD = 1µF
RLOAD = 10Ω, CLOAD = 1µF
600
1
800
1.5
1
1000
2
tR
ms
µs
tOFF
tF
5
24
µs
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 < 1.0V for MIC2042/MIC2043-1 and V > 4.0V for MIC2042/MIC2043-2. ON is V > 4.0V for MIC2042/MIC2043-1 and V < 1.0V for
EN
EN
EN
EN
MIC2042/MIC2043-2.
6. The current limit is determined as follows: I
= CLF/R
.
LIM
SET
Timing Diagrams
tOFF
50%
0
0
VEN
tON
90%
10%
VOUT
(a) MIC2042/43-1
50%
0
0
VEN
tOFF
tON
90%
10%
(b) MIC2042/43-2
VOUT
Figure 1. Turn-On/Turn-Off Delay
Increase the load
0
0
VEN
VIN 0.2V
VOUT
ILIMIT
0
IOUT
tFLAG
0
/FAULT
Figure 2. Overcurrent Fault Response — MIC2042-2
January 2005
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M0512-112603
MIC2042/2043
Micrel
Test Circuit
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January 2005
MIC2042/2043
Micrel
Typical Characteristics
Enable Input Threshold
(Falling)
vs. Temperature
Enable Input Threshold
(Rising)
Supply Current
vs. Temperature
vs. Temperature
3.5
3
500
3.5
3
450
VBIAS = 5.5V
VBIAS = 5.5V
400
2.5
2
2.5
2
VIN = VBIAS = 5.5V
350
VBIAS = 3V
VBIAS = 3V
300
1.5
1
1.5
1
VIN = VBIAS = 3V
250
VBIAS = 1.6V
VBIAS = 1.6V
VIN = VBIAS = 1.6V
200
0.5
0
0.5
0
150
100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Power-Good Reference
Threshold
vs. Temperature
Output Leakage Current
vs. Temperature
UVLO Threshold
vs. Temperature
600
500
400
300
200
100
0
230
225
220
215
210
1.55
1.5
VBIAS = 5.5V
VBIAS = 3V
1.45
1.4
UVLO+
VTH @ 1.6V to 5.5V
1.35
1.3
UVLO–
VBIAS = 1.6V
1.25
1.2
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
On Resistance
vs. Temperature
UVLO Adjust PinThreshold
vs. Temperature
Flag Response Delay
vs. Temperature
80
70
60
50
40
30
20
10
0
250
245
240
235
230
225
220
215
210
205
200
50
45
40
35
30
25
20
VIN = VBIAS = 1.6V
VIN = VBIAS = 3V
UVLO+
TFLAG = 5V
VIN = VBIAS = 5V
TFLAG = 3V
20 40 60 80 100
UVLO–
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
-40 -20
0
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
V
Reverse Current Flow
Turn-On Delay
vs. Temperature
BIAS
Slew Voltage
vs. Temperature
vs. Output Voltage
900
850
800
750
700
650
600
550
500
20
18
16
14
12
10
8
25
20
15
10
5
VIN = VBIAS = 5.5V
VIN = V BIAS = 5V
VIN = VBIAS = 3V
VIN = V BIAS = 3V
VIN = VBIAS = 1.6V
6
VIN = GND
VBIAS = 1.6V
4
VIN = V BIAS = 1.6V
2
0
0
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
2
2.5
3
3.5
V
4
4.5
(V)
5 5.5 6
TEMPERATURE (°C)
TEMPERATURE (°C)
OUT
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M0512-112603
MIC2042/2043
Micrel
Functional Characteristics
M0512-112603
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January 2005
MIC2042/2043
Micrel
January 2005
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M0512-112603
MIC2042/2043
Micrel
Functional Diagram
MIC2042/43 Block Diagram
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January 2005
MIC2042/2043
Micrel
Programmable Current Limit
Functional Description
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
TheMIC2042andMIC2043arehigh-sideN-Channelswitches
equipped with programmable current limit up to 3A for use in
generalpurposepowerdistributionapplications.Theswitches,
availablewithactive-highoractive-lowenableinputs,provide
output slew-rate control and circuit protection via thermal
shutdown and an optional output latch during overcurrent
conditions.
resistor (R
) connected from ILIM to ground and becomes
SET
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
and the MIC2042/43 will limit from 0.5A to 3A with a set point
,
SET
Input and Output
accuracy of ±22%. In programming the nominal current limit,
V
suppliespowertotheinternalcircuitryoftheswitchand
the value of R
is determined using the following equation:
BIAS
SET
must be present for the switch to operate. V is connected to
the drain of the output MOSFET and sources power to the
IN
390A × Ω
CLF
ILIMIT
(
=
)
RSET
=
(1)
switched load. V must be less than or equal to V
. V
ILIMIT
IN
BIAS OUT
is the source terminal of the output MOSFET and attaches to
the load. In a typical circuit, current flows from V to V
Andgiventhe±22%toleranceofthecurrentlimitfactor(CLF),
the external resistor is bound by:
IN
OUT
toward the load. If V
is greater than V , current will flow
OUT
IN
103Ω ≤ R
≤ 970Ω
(2)
from V
to V since the switch is bi-directional when the
SET
OUT
IN
deviceisenabled. Whendisabled(OFF), theswitchwillblock
current flow from either direction.
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
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. TheENpin, referencedtoapproximately0.5× 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.
V
(R
= V
= 3.0V and a nominal 2A current limit
IN
BIAS
= 192Ω), the low and high current limit settings for the
SET
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 V . If the VIN-to-VOUT differential voltage ex-
IN
Undervoltage Lockout
ceeds 200mV, then a fault condition is declared and the fault
delaytimerisstarted.Ifthefaultconditionpersistslongerthan
the delay period, typically 28ms, then the /FAULT output
asserts low. At this point, the MIC2042 will continue to supply
When the switch is enabled, undervoltage lockout (UVLO)
monitors the input voltage, V , and prevents the output
IN
MOSFET from turning on until V exceeds a predetermined
IN
level, nominally set at 1.45V. The UVLO threshold is adjust-
ableandcanbevariedbyapplyinganexternalresistordivider
to the UVLOIN pin from VIN to GND. The resistive divider
networkisrequiredwhentheinputvoltageisbelow1.5V. The
UVLO threshold is internally preset to 1.45V if the UVLOIN
pin is left open. See “Applications Information” section.
current to the load at the limiting value (I
MIC2043 will latch off its output.
), whereas the
LIMIT
Current Limit
Current Limit
Current Limit
vs. R
vs. R
vs. R
SET
SET
SET
4
3.5
3
4
3.5
3
4
3.5
3
–40°C to +85°C
VIN = VBIAS = 5V
–40°C to +85°C
VIN = VBIAS = 3V
–40°C to +85°C
VIN = VBIAS = 1.6V
2.5
2
2.5
2
2.5
2
CLF (HI)
CLF (HI)
CLF (HI)
1.5
1
1.5
1
1.5
1
CLF (LO)
CLF (LO)
0.5
0
0.5
0
0.5
0
CLF (LO)
0
120 240 360 480 600 720 840 960
(Ω)
0
120 240 360 480 600 720 840 960
(Ω)
0
120 240 360 480 600 720 840 960
(Ω)
R
R
R
SET
SET
SET
Figure 3. Current Limit Factor
January 2005
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MIC2042/2043
Micrel
/FAULT
off until either the fault load is removed from VOUT or the EN
inputiscycledON-OFF-ON. IfthefaultisstillpresentafterEN
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.
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
conditionoccurs. DuringahotinsertofaPCBorwhenturning
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.
Open Load Detection
TheMIC2043willautomaticallyresetitsoutputwhenthefault
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
Thermal Shutdown
TheMIC2042/43candetectwhentheoutputvoltageisabove
orbelowapresetthresholdthatismonitoredbyacomparator
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-
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/FAULToutputifthedietemperatureexceeds140°C.The
MIC2042automaticallyresetsitsoutputandresumessupply-
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.
old (V ), typically 230mV, the PWRGD output is asserted.
TH
Usingthetypicalapplicationscircuitfrompage1thatswitches
3.3V as an example, the output voltage threshold determin-
ing “power is good” is calculated by the following equation:
R2
R3
VOUT(GOOD) = VTH × 1+
(3)
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.
In substituting the resistor values of the circuit and the typical
PGREF threshold, the resulting V is calculated as
3.0V for this 3.3V switching application.
OUT(GOOD)
Slew
Circuit Breaker Function (MIC2043)
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
beachieved.Forfurtherdetail,seethe“ApplicationsInforma-
tion” section.
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
M0512-112603
12
January 2005
MIC2042/2043
Micrel
linear response. See the “Functional Characteristics” plots.
Table 1 shows the rise time for various standard capacitor
values.Additionally,theoutputturn-ontimemustbelessthan
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).
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.
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.ThecircuitshowninFigure4illustratesanapplication
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:
Output Capacitance
WhentheMIC2042dieexceedstheovertemperaturethresh-
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-
tralizedbycapacitanceinordertoensurethattheoutputdoes
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
capacitanceof22µFisstronglyrecommendedandshouldbe
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.
R2
R3
V
= 0.23V × 1+
(4)
UVTH
In substituting the resistor values from Figure 4, the resulting
UVLO threshold (V ) is calculated as 0.6V for this 0.8V
UVTH
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.
Reverse Current Block
The MIC2042/43 provides reverse current flow block through
theoutputMOSFETifthevoltageatVOUTisgreaterthanVIN
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
V
= V
= 5V/3V; C
= 47µF; I = 1A
LOAD
Conditions:
IN
BIAS
LOAD
V
reverse current flow is shown in the “Functional Char-
BIAS
acteristics” plots. The reverse current for V
can be
C
(µF)
Rise Time (ms)
BIAS
SLEW
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.
5V
3
3V
4.75
15
0.01
0.033
0.047
0.1
10.5
14
21
Output Slew-Rate Adjustment
32
46
Theoutputslew-ratefortheMIC2042/43canbesloweddown
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-
Table 1. Typical Output Rise Time for Various C
SLEW
January 2005
13
M0512-112603
MIC2042/2043
Micrel
Figure 4. Lower UVLO Setting
Power Dissipation
heatupconsiderably. Thefollowinglistcontainssomeuseful
suggestions for PCB layout design of the MIC2042/43 in
order to prevent the die from overheating under normal
operating conditions:
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.
1. Supply additional copper area under the device
to remove heat away from the IC.
Calculation of power dissipation can be accomplished by the
following equation:
2
See “Application Hint 17” for a general guideline
in calculating the suggested area.
P = R
× (I )
OUT
(5)
D
DS(ON)
To relate this to junction temperature, the following equation
can be used:
2. Provide additional pad area on the corner pins of
the MIC2042/43 IC for heat distribution.
T = P × Rθ + T
(6)
where T = junction temperature, T = ambient temperature
J
D
JA
A
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).
J
A
and Rθ is the thermal resistance of the package.
JA
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
currentduringhot-plugevents.Thissamefeaturealsocanbe
used for soft-start requirements.
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.
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
M0512-112603
14
January 2005
MIC2042/2043
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
45°
0.0098 (0.249)
0.0040 (0.102)
0.010 (0.25)
0.007 (0.18)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.064 (1.63)
0.045 (1.14)
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
4.50 (0.177)
4.30 (0.169)
DIMENSIONS:
MM (INCH)
6.4 BSC (0.252)
0.30 (0.012)
0.19 (0.007)
5.10 (0.200)
4.90 (0.193)
0.20 (0.008)
0.09 (0.003)
1.10 MAX (0.043)
0.65 BSC
(0.026)
1.00 (0.039) REF
8°
0°
0.15 (0.006)
0.05 (0.002)
0.70 (0.028)
0.50 (0.020)
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.
January 2005
15
M0512-112603
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