SLVS841D
– NOVEMBER 2008 – REVISED JUNE 2011
FAULT RESPONSE
The FAULT open-drain output is asserted (active low) during an overcurrent, overtemperature or reverse-voltage
condition. The TPS2552/53 asserts the FAULT signal until the fault condition is removed and the device resumes
normal operation. The TPS2552-1/53-1 asserts the FAULT signal during a fault condition and remains asserted
while the part is latched-off. The FAULT signal is de-asserted once device power is cycled or the enable is
toggled and the device resumes normal operation. The TPS2552/53 and TPS2552-1/53-1 are designed to
eliminate false FAULT reporting by using an internal delay "deglitch" circuit for overcurrent (7.5-ms typ) and
reverse-voltage (4-ms typ) conditions without the need for external circuitry. This ensures that FAULT is not
accidentally asserted due to normal operation such as starting into a heavy capacitive load. The deglitch circuitry
delays entering and leaving fault conditions. Overtemperature conditions are not deglitched and assert the
FAULT signal immediately.
UNDERVOLTAGE LOCKOUT (UVLO)
The undervoltage lockout (UVLO) circuit disables the power switch until the input voltage reaches the UVLO
turn-on threshold. Built-in hysteresis prevents unwanted on/off cycling due to input voltage drop from large
current surges.
ENABLE (EN OR EN)
The logic enable controls the power switch, bias for the charge pump, driver, and other circuits to reduce the
supply current. The supply current is reduced to less than 1-
μA when a logic high is present on EN or when a
logic low is present on EN. A logic low input on EN or a logic high input on EN enables the driver, control circuits,
and power switch. The enable input is compatible with both TTL and CMOS logic levels.
THERMAL SENSE
The TPS2552/53 and TPS2552-1/53-1 have self-protection features using two independent thermal sensing
circuits that monitor the operating temperature of the power switch and disable operation if the temperature
exceeds recommended operating conditions. The TPS2552/53 device operates in constant-current mode during
an overcurrent conditions, which increases the voltage drop across power-switch. The power dissipation in the
package is proportional to the voltage drop across the power switch, which increases the junction temperature
during an overcurrent condition. The first thermal sensor turns off the power switch when the die temperature
exceeds 135
°C (min) and the part is in current limit. Hysteresis is built into the thermal sensor, and the switch
turns on after the device has cooled approximately 10
°C.
The TPS2552/53 and TPS2552-1/53-1 also have a second ambient thermal sensor. The ambient thermal sensor
turns off the power-switch when the die temperature exceeds 155
°C (min) regardless of whether the power
switch is in current limit and will turn on the power switch after the device has cooled approximately 10
°C. Both
the TPS2552/53 and TPS2552-1/53-1 families continue to cycle off and on until the fault is removed.
The open-drain fault reporting output FAULT is asserted (active low) immediately during an overtemperature
shutdown condition.
12
Copyright
2008–2011, Texas Instruments Incorporated