ZHCSM35F January 2007 – May 2021 LM5002
PRODUCTION DATA
Soft start (SS) can be implemented with an external capacitor connected to COMP through a diode as shown in Figure 8-4. The COMP discharge MOSFET conducts during Shutdown and Standby modes to keep the COMP voltage below the PWM offset (1.3 V), which inhibits PWM pulses. The error amplifier attempts to raise the COMP voltage after the EN pin exceeds the 1.26 V standby threshold. Because the error amplifier output can only sink current, the internal COMP pullup resistor (approximately 5 kΩ) supplies the charging current to the SS capacitor. The SS capacitor causes the COMP voltage to gradually increase until the output voltage achieves regulation and FB assumes control of the COMP and the PWM duty cycle. The SS capacitor continues charging through a large resistance, RSS, preventing the SS circuit from interfering with the normal error amplifier function. During shutdown, the VCC diode discharges the SS capacitor.