TPS62933O datasheet(20/47 Pages) TI

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Frequency

Energy

Figure 8-8. Energy Versus Frequency

8.3.10 Overvoltage Protection

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

The OVP feature minimizes the overshoot by comparing the FB pin voltage to the OVP threshold. If the FB pin

voltage is greater than the OVP threshold of 115%, the high-side MOSFET is turned off, which prevents current

from flowing to the output and minimizes output overshoot. When the FB pin voltage drops lower than the OVP

threshold minus hysteresis, the high-side MOSFET is allowed to turn on at the next clock cycle. This function is

non-latch operation.

8.3.11 Overcurrent and Undervoltage Protection

The TPS62933 incorporates both peak and valley inductor current limits to provide protection to the device from

overloads and short circuits and limit the maximum output current. Valley current limit prevents inductor current

run-away during short circuits on the output, while both peak and valley limits work together to limit the maximum

output current of the converter. Hiccup mode is also incorporated for sustained short circuits.

The high-side switch current is sensed when it is turned on after a set blanking time (tON_MIN), the peak current

of high-side switch is limited by the peak current threshold, IHS_LIMIT. The current going through low-side switch

is also sensed and monitored. When the low-side switch turns on, the inductor current begins to ramp down.

As the device is overloaded, a point is reached where the valley of the inductor current cannot reach below

ILS_LIMIT before the next clock cycle, then the low-side switch is kept on until the inductor current ramps below

the valley current threshold, ILS_LIMIT, then the low-side switch is turned off and the high-side switch is turned

on after a dead time. When this occurs, the valley current limit control skips that cycle, causing the switching

frequency to drop. Further overload causes the switching frequency to continue to drop, but the output voltage

remains in regulation. As the overload is increased, both the inductor current ripple and peak current increase

until the high-side current limit, IHS_LIMIT, is reached. When this limit is tripped, the switch duty cycle is reduced

and the output voltage falls out of regulation. This represents the maximum output current from the converter

and is given approximately by Equation 11. The output voltage and switching frequency continue to drop as the

device moves deeper into overload while the output current remains at approximately IOMAX. There is another

situation, if the inductor ripple current is large, the high-side current limit can be tripped before the low-side limit

is reached. In this case, Equation 12 gives the approximate maximum output current.

HS _ LIMIT

LS _ LIMIT

OMAX

(11)

u u

OUT

OMAX

HS _ LIMIT

(V -V

)

L f

(12)

TPS62933

SLUSEA4A – JUNE 2021 – REVISED DECEMBER 2021

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