Datasheet

TPS65251

SLVSAA4D –JUNE 2010–REVISED DECEMBER 2012

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Figure 26 shows the (peak) inductor current limit for Buck 3. The typical limit can be approximated with the

following graph.

Figure 26. Buck 3

All converters operate in hiccup mode: Once an over-current lasting more than 10 ms is sensed in any of the

converters, all the converters will shut down for 10 ms and then the start-up sequencing will be tried again. If the

overload has been removed, the converter will ramp up and operate normally. If this is not the case the converter

will see another over-current event and shuts-down again repeating the cycle (hiccup) until the failure is cleared.

If an overload condition lasts for less than 10 ms, only the relevant converter affected will go into and out of

under-voltage and no global hiccup mode will occur. The converter will be protected by the cycle-by-cycle current

limit during that time.

Overvoltage Transient Protection

The device incorporates an overvoltage transient protection (OVP) circuit to minimize voltage overshoot. The

OVP feature minimizes the output overshoot by implementing a circuit to compare the FB pin voltage to OVP

threshold which is 109% of the internal voltage reference. If the FB pin voltage is greater than the OVP threshold,

the high side MOSFET is disabled preventing current from flowing to the output and minimizing output overshoot.

When the FB voltage drops below the lower OVP threshold which is 107%, the high side MOSFET is allowed to

turn on the next clock cycle.

Thermal Shutdown

The device implements an internal thermal shutdown to protect itself if the junction temperature exceeds 160°C.

The thermal shutdown forces the device to stop switching when the junction temperature exceeds thermal trip

threshold. Once the die temperature decreases below 140°C, the device reinitiates the power up sequence. The

thermal shutdown hysteresis is 20°C.

Product Folder Links: TPS65251