SBVS343A March 2019 – September 2019 TPS7A78
A load-transient event can trigger the internal overcharge protection circuit on the LDO_IN pin. This condition prevents CLDO_IN from overcharging when a heavy load is abruptly removed. The overvoltage protection circuit engages and prevents the switched capacitors from switching until the excess charge on CLDO_IN is discharged into the load. This protection behavior occurs most often during heavy load-transient events on devices with higher output voltages. The value of the CLDO_IN capacitor and the load current determine how long the overvoltage protection circuit remains engaged. Figure 21 shows the overvoltage protection circuit behavior after the load is removed without tripping the PG signal.
As illustrated in Figure 22, a load-transient event that exceeds the maximum output current can disable the output when the heavy load pulls down the VLDO_IN voltage below the VUVLO_LDO_IN falling threshold. If the application is prone to heavy load-transient events as illustrated in Figure 22, increase the CLDO_IN capacitor value as necessary. However, as illustrated in Figure 20, too large of a CLDO_IN leads to a longer startup time.
|VAC = 120 VRMS at 60 Hz, FB, CLDO_IN = 10 µF,
VLDO_OUT = 3.3 V, IOUT = 1 mA to 600 mA,
current slew = 1 A/µs
|VAC = 120 VRMS at 60 Hz, FB, CLDO_IN = 56 µF,
VLDO_OUT = 3.3 V, IOUT = 1 mA to 600 mA, current slew = 1 A/µs