TPS2556

TPS2557

SLVS931A

– NOVEMBER 2009 – REVISED FEBRUARY 2012

www.ti.com

FAULT RESPONSE

The FAULT open-drain output is asserted (active low) during an overcurrent or overtemperature condition. The

TPS2556/57 asserts the FAULT signal until the fault condition is removed and the device resumes normal

operation. The TPS2556/57 is designed to eliminate false FAULTreporting by using an internal delay "deglitch"

circuit for overcurrent (9-ms typ) conditions without the need for external circuitry. This ensures that FAULTis not

accidentally asserted due to normal operation such as starting into a heavy capacitive load. The deglitch circuitry

delays entering and leaving current-limit induced fault conditions. The FAULTsignal is not deglitched when the

MOSFET is disabled due to an overtemperature condition but is deglitched after the device has cooled and

begins to turn on. This unidirectional deglitch prevents FAULT oscillation during an overtemperature event.

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 droop during turn on.

ENABLE (EN OR EN)

The logic enable controls the power switch and device supply current. The supply current is reduced to less than

2-

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 TPS2556/57 self protects by 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 TPS2556/57 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 (OTSD) 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 20

°C.

The TPS2556/57 also has a second ambient thermal sensor (OTSD2). 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 20

°C. The TPS2556/57

continues to cycle off and on until the fault is removed.

APPLICATION INFORMATION

INPUT AND OUTPUT CAPACITANCE

Input and output capacitance improves the performance of the device; the actual capacitance should be

optimized for the particular application. For all applications, a 0.1

μF or greater ceramic bypass capacitor between

IN and GND is recommended as close to the device as possible for local noise decoupling. This precaution

reduces ringing on the input due to power-supply transients. Additional input capacitance may be needed on the

input to reduce voltage overshoot from exceeding the absolute-maximum voltage of the device during heavy

transient conditions. This is especially important during bench testing when long, inductive cables are used to

connect the evaluation board to the bench power supply.

Output capacitance is not required, but placing a high-value electrolytic capacitor on the output pin is

recommended when large transient currents are expected on the output.

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Product Folder Link(s): TPS2556 TPS2557