JAJSH64B November 2012 – April 2019 TPS53819A
PRODUCTION DATA.
TPS53819A has cycle-by-cycle overcurrent limiting control. The inductor current is monitored during the OFF state and the controller maintains the OFF state during the period when inductor current is larger than the overcurrent trip level. In order to provide both good accuracy and cost effective solution, TPS53819A supports temperature compensated MOSFET on-resistance (RDS(on)) sensing. The TRIP pin should be connected to GND through the trip voltage setting resistor, RTRIP. The TRIP terminal sources ITRIP current, which is 10 μA typically at room temperature, and the trip level is set to the OCL trip voltage VTRIP as shown in Equation 4. Note that the VTRIP is limited up to approximately 3 V internally.
The inductor current is monitored by the voltage between GND pin and SW pin so that SW pin should be properly connected to the drain terminal of the low-side MOSFET. The TRIP current has a 4700-ppm/°C temperature slope to compensate the temperature dependency of the on-resistance. The device uses the GND pin as the positive current sensing node. As the comparison occurs during the OFF state, VTRIP sets the valley level of the inductor current. Thus, the average load current at the overcurrent threshold, IOCP, is calculated as shown in Equation 5.
In an overcurrent condition, the load current exceeds the inductor current delivered to the output capacitor, thus the output voltage tends to fall. Eventually, it crosses the undervoltage protection threshold and the device shuts down. If hiccup mode is selected, then after a hiccup delay time (8.96 ms + 7× programmed soft-start time), the controller restarts. If the overcurrent condition remains, the procedure is repeated and the device enters hiccup mode. During the CCM, the negative current limit (NCL) protects the external FET from carrying too much current. The OCLN detect threshold is set at the same absolute value as positive current limit (OCLP) but with negative polarity. Note that the threshold still represents the valley value of the inductor current. When an OCLP or OCLN event occurs, the corresponding fault signals (IOUT_OC and IOUT) of the STATUS_WORD register is latched to indicate the faults and can be read via PMBus.