MIC2040/2041

Micrel

M9999-012004

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

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 140°C. The

MIC2040 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 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.