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2015-08-0011

PT0497-4

08/31/15

8

PI5PD2556/2557

Precision Adjustable

Current-Limited Power Switch

Over-current Conditions

When an over-current condition is detected, the device maintains a constant output current and reduces the output voltage

accordingly.

The PI5PD2556/2557 thermal cycles if an overload condition is present long enough to activate thermal limiting in any of the

above cases. The device turns off when the junction temperature exceeds 135°C (min) while in current limit. The device remains

off until the junction temperature cools 20°C (typ) and then restarts. The PI5PD2556/2557 cycles on/off until the overload is

removed.

/FAULT Response

The FAULT open-drain outputs are asserted (active low) during an over-current or over-temperature condition. The

PI5PD2556/2557 asserts the FAULTx signal until the fault condition is removed and the device resumes normal operation. The

PI5PD2556/2557 is designed to eliminate false FAULT reporting by using an internal delay "deglitch" circuit (9-ms typ) for over-

current 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 current-limited induced

fault conditions. The FAULT signal is not deglitched when the MOSFET is disabled due to an over-temperature condition but is

deglitched after the device has cooled and begins to turn on. This unidrectional deglitch prevents FAULT oscillation during an

over-temperature event.

Under-voltage Lockout (UVLO)

The under-voltage 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 enables control the power switches 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 switches. The enable inputs are compatible with both TTL and CMOS logic levels.

Thermal Sense

The PI5PD2556/2557 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 PI5PD2556/2557 operates

in constant-current mode during an over-current condition, which increases the voltage drop across the 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 over-current condition. The first thermal sensor (OTSD) turns off the power switch when the die temperature exceeds

135°C (min) and the chip 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 PI5PD2556/2557 also has a second ambient thermal sensor (OTSD2). The ambient thermal sensor turns off

power switch

when the die temperature exceeds 155°C (min) regardless of whether the power switch are in current limit and will turn on the

power switches after the device has cooled approximately 20°C. The PI5PD2556/2557 continues to cycle off and on until the fault

is removed.