SLVS930 – DECEMBER 2009
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DETAILED DESCRIPTION
OVERVIEW
The TPS2560/61 is a dual-channel, current-limited power-distribution switch using N-channel MOSFETs for
applications where short circuits or heavy capacitive loads will be encountered. This device allows the user to
program the current-limit threshold between 250 mA and 2.8 A (typ) per channel via an external resistor. This
device incorporates an internal charge pump and gate drive circuitry necessary to drive the N-channel
MOSFETs. The charge pump supplies power to the driver circuit for each channel 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 2.5 V and requires little supply current. The driver controls the gate voltage of the power switch. The driver
incorporates circuitry that controls the rise and fall times of the output voltage to limit large current and voltage
surges and provides built-in soft-start functionality. Each channel of the TPS2560/61 limits the output current to
the programmed current-limit threshold IOS during an overcurrent or short-circuit event by reducing the charge
pump voltage driving the N-channel MOSFET and operating it in the linear range of operation. The result of
limiting the output current to IOS reduces the output voltage at OUTx because the N-channel MOSFET is no
longer fully enhanced.
OVERCURRENT CONDITIONS
The TPS2560/61 responds to overcurrent conditions by limiting the output current per channel to IOS. When an
overcurrent condition is detected, the device maintains a constant output current and reduces the output voltage
accordingly. Two possible overload conditions can occur.
The first condition is when a short circuit or partial short circuit is present when the device is powered-up or
enabled. The output voltage is held near zero potential with respect to ground and the TPS2560/61 ramps the
output current to IOS. The TPS2560/61 devices will limit the current to IOS until the overload condition is removed
or the device begins to thermal cycle.
The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device is
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 internal current-limit
MOSFET. The current-sense amplifier recovers and ramps the output current to IOS. Similar to the previous case,
the TPS2560/61 will limit the current to IOS until the overload condition is removed or the device begins to thermal
cycle.
The TPS2560/61 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 TPS2560/61
cycles on/off until the overload is removed (see
Figure 9) .
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