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TPS25221

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SLVSDT3 – JANUARY 2018

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Copyright © 2018, Texas Instruments Incorporated

10 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

10.1 Application Information

10.1.1 Constant-Current

The TPS25221 operates identically during normal operation, that is, the load current is less than the current-limit

threshold and the devices are not limiting current. During normal operation, The TPS25221 load current is less

than the current-limit threshold and the devices are not limiting current. During normal operation the N-channel

The TPS25221 operates identically during the initial onset of an overcurrent event. The TPS25221 limits current

During current-limit operation, the N-channel MOSFET is no longer fully-enhanced and the resistance of the

device increases. This allows the device to effectively regulate the current to the current-limit threshold. The

effect of increasing the resistance of the MOSFET is that the voltage drop across the device is no longer

where:

(2)

The TPS25221 operates identically during the initial onset of an overcurrent event, it behaves differently if the

overcurrent event lasts longer than the internal delay de-glitch circuit (8 ms typical). The TPS25221 asserts the

FAULT flag after the deglitch period and continue to regulate the current to the current-limit threshold indefinitely.

In practical circuits, the power dissipation in the package increases the die temperature above the thermal

shutdown current limit threshold (145°C typical), and the device turns off until the die temperature decreases by

the hysteresis of the thermal shutdown circuit (20°C typical). The device turns on and continues to thermal cycle

until the overload condition is removed. The constant-current device resumes normal operation once the

overload condition is removed.

10.2 Typical Applications

10.2.1 Two-Level Current-Limit Circuit

Some applications require different current-limit thresholds depending on external system conditions. Figure 20

shows an implementation for an externally controlled, two-level current-limit circuit. The current-limit threshold is

set by the total resistance from ILIM to GND (see the Programming the Current-Limit Threshold section). A logic-

level input enables or disables MOSFET Q1 and changes the current-limit threshold by modifying the total

resistance from ILIM to GND. Additional MOSFET and resistor combinations can be used in parallel to Q1/R2 to

increase the number of additional current-limit levels.

NOTE

ILIM must never be driven directly with an external signal.