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DETAILED DESCRIPTION

POWER SWITCH

Charge Pump

Driver

Enable (EN)

Overcurrent (OC)

Current Sense

Thermal Sense

Undervoltage Lockout

TPS2014

TPS2015

SLVS159D – DECEMBER 1996 – REVISED SEPTEMBER 2007

The power switch is an N-channel MOSFET with a maximum on-state resistance of 95 m

configured as a high-side switch.

An internal 100-kHz charge pump supplies power to the driver circuit and provides the necessary voltage to pull

the gate of the MOSFET above the source. The charge pump operates from input voltages as low as 4 V and

requires very little supply current.

The driver controls the gate voltage of the power switch. To limit large current surges and reduce the associated

electromagnetic interference (EMI) produced, the driver incorporates circuitry that controls the rise times and fall

times of the output voltage. The rise and fall times are typically in the 2-ms to 4-ms range instead of the

microsecond or nanosecond range for a standard FET.

A logic high on EN turns off the power switch and the bias for the charge pump, driver, and other circuitry to

reduce the supply current to less than 10 A. A logic zero input restores bias to the drive and control circuits and

turns the power on. The enable input is compatible with both TTL and CMOS logic levels.

OC is an open-drain logic output that is asserted (active low) when an overload or short circuit is encountered.

The output remains asserted until the overload or short-circuit condition is removed.

A sense FET monitors the current supplied to the load. The sense FET provides a much more efficient way to

measure current than conventional resistance methods. When an overload or short circuit is encountered, the

current-sense circuitry sends a control signal to the driver. The driver in turn reduces the gate voltage and drives

the power FET into its linear region, which switches the output into a constant current mode and simply holds the

current constant while varying the voltage on the load.

An internal thermal-sense circuit shuts off the power switch when the junction temperature rises to approximately

to 180C. Hysteresis is built into the thermal sense circuit. After the device has cooled approximately 20C, the

switch turns back on. The switch continues to cycle off and on until the fault is removed.

An internal voltage sense monitors the input voltage. When the input voltage is below 3.2 V nominal, a control

signal turns off the power switch.

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