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
MICREL [ MICREL SEMICONDUCTOR ]
