ZHCSKC0 October 2019 UCC21736-Q1
ADVANCE INFORMATION for pre-production products; subject to change without notice.
When VCC loses power, or MCU is malfunctional, the motor can lose control and reversely charging the battery. Overvoltage of the battery can cause battery break down, or even the fire hazard. In this case, the active short circuit (ASC) function is used to protect the system by forcing the output signal high, turning on the switch and creating an active short circuit loop between the phases to bypass the battery. The timing diagram of ASC protection with VCC UVLO, VDD UVLO and OC fault are shown in Figure 36, Figure 37, and Figure 38.
The UCC21736-Q1 encodes the voltage signal VASC to a PWM signal, passing through the reinforced isolation barrier, and output to APWM pin on the input side. Thus the ASC pin status can be monitored. The PWM signal can either be transferred directly to DSP/MCU to calculate the duty cycle, or filtered by a simple RC filter as an analog signal. The ASC input voltage varies from 0V to 5V, and the corresponding duty cycle of the APWM output ranges from 95% to 5% with 400kHz frequency.