ZHCS819G March 2012 – March 2018 DRV110
The keep time, tKEEP, is set externally by connecting a capacitor to the KEEP pin. A constant current is sourced from the KEEP pin that is driven into an external capacitor resulting in a linear voltage ramp. When the KEEP pin voltage reaches 100 mV, the current regulation reference voltage, VREF, is switched from VPEAK to VHOLD. The internal current source is switched off, and the capacitor is grounded for discharge. The dependency of tKEEP from the external capacitor size can be calculated with Equation 1.