TIDUF28 November 2023
The TIDA-010255 provides an option to sense the three phase voltages with an analog-to-digital converter, typically integrated in the hot-side control MCU. Due to the very low dead-time of the LMG3422R030 GaN-FETs of 100 ns, the phase voltage can accurately be estimated using the PWM duty cycle and the DC-link voltage.
The phase voltage to GND is sensed using a high-voltage resistor divider and a low-pass filter to attenuate the PWM switching frequency. The high-impedance resistor divider R7, R18, R55, and R4 is scaled to provide a 3-V signal at a 480-VDC phase to GND voltage. The low-pass filter R58 and C49 has a cutoff frequency of 360 Hz to attenuate the PWM carrier frequency. Schottky diodes to clamp the maximum voltage at V_PHASE to around 3.6 V are not added intentionally, since the voltage is not supposed to exceed 3 V even during operating conditions with 480-VDC transient DC-link voltage, while the 360-Hz low-pass filter needs to suppress high-frequency transients.