ZHCS819G March 2012 – March 2018 DRV110
The current control loop regulates, cycle-by-cycle, the solenoid current by sensing voltage at the SENSE pin and controlling the external switching device gate through the OUT pin. During the ON-cycle, the OUT pin voltage is driven and kept high (equal to VIN voltage) allowing current to flow through the external switch as long as the voltage at the SENSE pin is less than VREF. As soon as the voltage at the SENSE pin is above VREF, the OUT pin voltage is immediately driven low and kept low until the next ON-cycle is triggered by the internal PWM clock signal. In the beginning of each ON-cycle, the OUT pin voltage is driven high and kept high for at least the time determined by the minimum PWM signal duty cycle, DMIN.
Because the current sense is done by comparing the voltage at the SENSE pin to a reference voltage, the DRV110 device acts like a hysteresis controller. When the device acts like a hysteresis controller, it can make the PWM frequency and duty cycle appear uneven for some solenoids (see Figure 3).