Datasheet

TPS65250

SLVSAA3C –JUNE 2010–REVISED OCTOBER 2012

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Figure 35. Buck 3

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

converters, they will shuts 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 OVTP

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

threshold, the high side MOSFET is disabled preventing current from flowing to the output and minimizing output

overshoot. When the FB voltage drops lower than the OVTP 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.

Power Dissipation

The total power dissipation inside TPS65250 should not to exceed the maximum allowable junction temperature

of 125°C. The maximum allowable power dissipation is a function of the thermal resistance of the package (R

)

and ambient temperature.

To calculate the temperature inside the device under continuous loading use the following procedure.

1. Define the set voltage for each converter.

2. Define the continuous loading on each converter. Make sure do not exceed the converter maximum loading.

3. Determine from the graphs below the expected losses in watts per converter inside the device. The losses

depend on the input supply, the selected switching frequency, the output voltage and the converter chosen.

4. To calculate the maximum temperature inside the IC use the following formula:

Product Folder Links: TPS65250