ZHCSI22F October 2017 – December 2021 TPS2662
The devices are designed to control the inrush current upon insertion of a card into a live backplane or other hotpower source. This design limits the voltage sag on the backplane’s supply voltage and prevents unintended resets of the system power. The controlled start-up also helps to eliminate conductive and radiative interferences. An external capacitor connected from the dVdT pin to RTN defines the slew rate of the output voltage at power-on as shown in Figure 9-2 and Figure 9-3.
The dVdT pin can be left floating to obtain a predetermined slew rate (tdVdT) on the output. When the terminal is left floating, the devices set an internal output voltage ramp rate of 24 V/660 µs. A capacitor can be connected from dVdT pin to RTN to program the output voltage slew rate slower than 24 V/660 µs. Use Equation 1 and Equation 2 to calculate the external C(dVdT) capacitance.
Equation 1 governs slew rate at start-up.
The total ramp time (tdVdT) of V(OUT) for 0 to V(IN) can be calculated using Equation 2.
|CdVdT = 22 nF||COUT = 22 µF||RILIM = 7.5 kΩ|