JAJSJT8C May 2020 – June 2021 TPS543620
The current is sensed in the high-side MOSFET while it is conducting after a short blanking time to allow noise to settle. Whenever the high-side overcurrent threshold is exceeded, the high-side MOSFET is immediately turned off and the low-side MOSFET is turned on. The high-side MOSFET does not turn back on until the current falls below the low-side MOSFET overcurrent threshold. This effectively limits the peak current in the case of a short circuit condition. If a high-side overcurrent is detected for 15 consecutive cycles, the device enters hiccup.
The current is also sensed in the low-side MOSFET while it is conducting after a short blanking time to allow noise to settle. If the low-side overcurrent threshold is exceeded when the next incoming PWM signal is received from the controller, the device skips processing that PWM pulse. The device does not turn the high-side MOSFET on again until the low-side overcurrent threshold is no longer exceeded. If the low-side overcurrent threshold remains exceeded for 15 consecutive cycles, the device enters hiccup. There are two separate counters for the high-side and low-side overcurrent events. If the off-time is too short, the low-side overcurrent may not trip. The low-side overcurrent will, however, begin tripping after the high-side peak overcurrent limit is hit as hitting the peak current limit shortens the on-time and lengthens the off-time.
Both the high-side and low-side positive overcurrent thresholds are programmable using the MODE pin. Two sets of thresholds are available ("High" and "Low"), which are summarized in Table 7-5. The values for these thresholds are obtained using open-loop measurements with a DC current in order to accurately specify the values. In real applications, the inductor current will ramp and the ramp rate will be a function of the voltage across the inductor (VIN - VOUT) as well as the inductance value. This ramp rate combined with delays in the current sense circuitry can result in slightly different values than specified. The current at which the high-side overcurrent limit takes effect can be slightly higher than specified, and the current at which the low-side overcurrent limit takes effect can be slightly lower than specified.
|MODE PIN CURRENT LIMIT SETTING||HIGH-SIDE OVERCURRENT TYPICAL VALUE (A)||LOW-SIDE OVERCURRENT TYPICAL VALUE (A)|