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ENABLE (EN OR EN)

THERMAL SENSE

TPS2550

TPS2551

SLVS736 – FEBRUARY 2008

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.

The TPS2550/51 protects itself with two independent thermal sensing circuits that monitor the operating

temperature of the power-switch and disables operation if the temperature exceeds recommended operating

conditions. The 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, so the junction temperature rises during an overcurrent condition. The first thermal

sensor turns off the power-switch when the die temperature exceeds 135

°C and the part is in current limit. The

second thermal sensor turns off the power-switch when the die temperature exceeds 155

°C regardless of

whether the power-switch is in current limit. Hysteresis is built into both thermal sensors, and the switch turns on

after the device has cooled approximately 15

°C. The switch continues to cycle off and on until the fault is

removed. The open-drain false reporting output FAULT is asserted (active low) immediately during an

overtemperature shutdown condition.

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