TPS2500, TPS2501

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SLVS886C – OCTOBER 2008 – REVISED AUGUST 2010

POWER SWITCH

Overview

The TPS2500 integrates a current-limited, power-distribution switch using an N-channel MOSFET for applications

where short circuits or heavy capacitive loads are encountered. The current-limit threshold is user-programmable

between 130 mA and 1.4 A (typical) by selecting an external resistor. The device incorporates an internal charge

pump and gate-drive circuitry necessary to fully enhance the N-channel MOSFET. The internal gate driver

controls the MOSFET turnon to limit large current and voltage surges by providing built-in soft-start functionality.

The power switch has an independent undervoltage lockout (UVLO) circuit that disables the power switch until

the voltage on AUX reaches 4.3 V (typical). Built-in hysteresis prevents unwanted on/off cycling due to input

voltage drop on AUX from current surges on the output of the power switch. The power switch has an

independent logic-level enable control (ENUSB) that gates power-switch turnon and bias for the charge pump,

driver, and miscellaneous control circuitry. A logic-high input on ENUSB enables the driver, control circuits, and

power switch. The enable input is compatible with CMOS, TTL, LVTTL, 2.5-V, and 1.8-V logic levels.

Overcurrent Conditions

The TPS2500 power switch responds to overcurrent conditions by limiting its output current to the IOS levels

shown in Figure 4. The device maintains a constant output current and reduces the output voltage accordingly

during an overcurrent condition. Two possible overload conditions can occur.

The first condition is when a short circuit or partial short circuit is present on the output of the switch prior to

device turnon and the device is powered up or enabled. The output voltage is held near zero potential with

respect to ground, and the TPS2500 ramps the output current to IOS. The TPS2500 power switch limits the

current to IOS until the overload condition is removed or the device begins to cycle thermally.

The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device is

already enabled and powered on. The device responds to the overcurrent condition within time tIOS (see

Figure 3). The current-sense amplifier is overdriven during this time and momentarily disables the power switch.

The current-sense amplifier recovers and limits the output current to IOS. The power switch thermally cycles if an

overload condition is present long enough to activate thermal limiting in any of the foregoing cases. The power

switch turns off when the junction temperature exceeds 130°C while in current-limit. The power switch remains

off until the junction temperature cools 10°C and then restarts. The TPS2500 power switch cycles on/off until the

overload is removed. The boost converter is independent of the power-switch thermal sense and continues to

operate as long as the temperature of the boost converter remains less than 150°C and does not trigger the

boost-converter thermal sense.

FAULT Response

The FAULT open-drain output is asserted low during an overcurrent condition that causes VUSB to fall below

VTRIP (4.6 V typical) or causes the junction temperature to exceed the shutdown threshold (130°C). The TPS2500

asserts the FAULT signal until the fault condition is removed and the power switch resumes normal operation.

The FAULT signal is independent of the boost converter. The FAULT signal uses an internal delay deglitch circuit

(8-ms typical) to delay asserting the FAULT signal during an overcurrent condition. The power switch must

remain in an overcurrent condition for the entire deglitch period or the deglitch timer is restarted. 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.

Power Switch Undervoltage Lockout

The undervoltage lockout (UVLO) circuit disables the TPS2500 power switch until the input voltage on AUX

reaches the power switch UVLO turn-on threshold of 4.3 V (typical). Built-in hysteresis prevents unwanted on/off

cycling due to input-voltage drop from large current surges.

Power Switch Enable

The logic enable controls the power switch, bias for the charge pump, driver, and other circuits to reduce the

supply current of the power switch. The power-switch supply current is reduced to less than 4 mA (typical) when

a logic-low input is present on ENUSB. A logic-high input on ENUSB enables the driver, control circuits, and

power switch. The enable input is compatible with both TTL and CMOS logic levels.

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Product Folder Link(s): TPS2500 TPS2501