Hello,

In the "Typical application" for gate drivers, a resistor and a capacitor are located between the output of the pwm MCU and the driver, but nowhere is it said about their role.

From what I've found it looks like a Low-Pass filter, but I don't know if it is.
Driver datasheet

Questions:
1) Why is it necessary?
2) What is the calculation method? (PWM 100kHz, 3.3V)
3) If two drivers are used (each Half-Bridge), they have two common lines (HPWM and LPWM), do I need to put this capacitor and resistor near each driver? (in total, there are 4 resistors and a capacitor for two drivers). Or a resistor and a capacitor on both lines.
4) In my case, I also use an external digital isolator (BL7140WH) to isolate the PWM. He has his primary and secondary side. Is a filter required on each side of the insulator?





Thank you!

 

Hello,

In the "Typical application" for gate drivers, a resistor and a capacitor are located between the output of the pwm MCU and the driver, but nowhere is it said about their role.
View attachment 300110
From what I've found it looks like a Low-Pass filter, but I don't know if it is.
Driver datasheet

Questions:
1) Why is it necessary?
2) What is the calculation method? (PWM 100kHz, 3.3V)
3) If two drivers are used (each Half-Bridge), they have two common lines (HPWM and LPWM), do I need to put this capacitor and resistor near each driver? (in total, there are 4 resistors and a capacitor for two drivers). Or a resistor and a capacitor on both lines.
4) In my case, I also use an external digital isolator (BL7140WH) to isolate the PWM. He has his primary and secondary side. Is a filter required on each side of the insulator?

View attachment 300111



Thank you!

Section 8.2.2.6 of the datasheet gives you the information you need, so no, you would only need it on the output side of the BL7140, if at all!
P.S. Your datasheet is for a different driver!

 

This article may explain why a low-pass filter would be used for the Hin and Lin inputs.

 

sarahMCML,
Alec_t
Thank you for the answer!

I use this driver (from ST), whose datasheet I attached to the topic. The picture shows an example of a low-pass filter from another driver.

I studied this article, I will use a low pass filter.

The question is, what cutoff frequency should be used so as not to distort the PWM signal? The higher the frequency, the lower the filter capacitance and distortion (I use PWM 3.3V, 100kHz, 50%).

Example:
1) Fswx = 100kHz, Fcutoff = 100kHz, R = 220Ohm, C 7.24nF

2) Fswx = 100kHz, Fcutoff = 550kHz, R = 220Ohm, C 1.32nF