TPS54627

SLVSBW6A – APRIL 2013 – REVISED SEPTEMBER 2013

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monitors the low-side FET switch voltage, which is proportional to the switch current, during the low-side on-time.

If the measured voltage is above the voltage proportional to the current limit, an internal counter is incremented

per each SW cycle and the converter maintains the low-side switch on until the measured voltage is below the

voltage corresponding to the current limit at which time the switching cycle is terminated and a new switching

cycle begins. In subsequent switching cycles, the on-time is set to a fixed value and the current is monitored in

the same manner. If the over current condition exists for 7 consecutive switching cycles, the internal OCL

threshold is set to a lower level, reducing the available output current. When a switching cycle occurs where the

switch current is not above the lower OCL threshold, the counter is reset and the OCL limit is returned to the

higher value.

There are some important considerations for this type of over-current protection. The peak current is the average

load current plus one half of the peak-to-peak inductor current. The valley current is the average load current

minus one half of the peak-to-peak inductor current. Since the valley current is used to detect the over-current

threshold, the load current is higher than the over-current threshold. Also, when the current is being limited, the

output voltage tends to fall. When the VFB voltage becomes lower than 65% of the target voltage, the UVP

comparator detects it. If the under-voltage condition persists for 250 µs, the device will shut down and re-start in

hiccup mode after 7 times the SS period. When the over current condition is removed, the output voltage will

return to the regulated value. This protection is non-latching.

Over Voltage Protection

TPS54627 detects over and under voltage conditions by monitoring the feedback voltage (VFB). This function is

enabled after approximately 1.7 x times the soft start time. When the feedback voltage becomes higher than

125% of the target voltage, the OVP comparator output goes high and both the high-side MOSFET driver and

the low-side MOSFET driver turn off. This function is non-latch operation.

UVLO Protection

than UVLO threshold voltage, the TPS54627 is shut off. This protection is non-latching.

Thermal Shutdown

TPS54627 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 165°C),

the device is shut off. This is non-latch protection.

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