TPS560200

SLVSC81 – SEPTEMBER 2013

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Current Protection

The output over-current protection (OCP) is implemented using a cycle-by-cycle valley detect control circuit. The

switch current is monitored by measuring the low-side FET switch voltage between the PH pin and GND. This

voltage is proportional to the switch current. To improve accuracy, the voltage sensing is temperature

compensated.

decreases linearly. The average value of the switch current is the load current Iout. The TPS560200 constantly

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 switching 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.

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 overcurrent

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

output voltage tends to fall as the demanded load current may be higher than the current available from the

converter. This protection is non-latching. When the VSENSE voltage becomes lower than 63% of the target

voltage, the UVP comparator detects it. After 7 µs detecting the UVP voltage, device shuts down and re-starts

after hiccup time.

When the over-current condition is removed, the output voltage returns to the regulated value.

Thermal Shutdown

TPS560200 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 170°C),

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

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