LMZ31520 Datasheet, PDF (19/30 Pages) Texas Instruments – 20A SIMPLE SWITCHER® Power Module with 3.0V-14.5V Input in QFN Package

LMZ31520
www.ti.com
SLVSBM9B – OCTOBER 2013 – REVISED DECEMBER 2013
Overcurrent Protection
For protection against load faults, the LMZ31520 incorporates cycle-by-cycle overcurrent limiting control. The
inductor current is monitored during the OFF state and the controller maintains the OFF state during the period in
that the inductor current is larger than the overcurrent trip level. In cycle-by-cycle mode, applying a load that
exceeds the regulator's overcurrent threshold limits the output current and reduces the output voltage as shown
in Figure 23. If the overcurrent condition remains and the output voltage drops below 70% of the set-point, the
LMZ31520 shuts down. Following shutdown, the module periodically attempts to recover by initiating a soft-start
power-up as shown in Figure 23. This is described as a hiccup mode of operation, whereby the module
continues in a cycle of successive shutdown and power up until the load fault is removed. During this period, the
average current flowing into the fault is significantly reduced which reduces power dissipation. Once the fault is
removed, the module automatically recovers and returns to normal operation as shown in Figure 24.
Figure 23. Typical Overcurrent Limiting
Figure 24. Typical Removal of Overcurrent
Current Limit (ILIM) Adjust
The current limit of this device can be adjusted lower by connecting a resistor, R_ILIM, between the ILIM pin (pin 6)
and PGND. To adjust the typical current limit threshold, as listed in the electrical characteristics table, refer to
Table 6.
Table 6. Current Limit Adjust Resistor
Current Limit Reduction
10 %
20 %
30 %
R_ILIM (kΩ)
715
383
243
Thermal Shutdown
The internal thermal shutdown circuitry forces the device to stop switching if the junction temperature exceeds
145°C typically. The device reinitiates the power up sequence when the junction temperature drops below 135°C
typically.
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