PWM signal to S12ZVL,how to select filter capacitor?

[jy1]

PWM signal to S12ZVL,how to select filter capacitor?

[tomasfedor]

Hi jy1, 

I checked the picture you had shared. I noticed HALL signal there. 

Am I getting it correctly that you want to measure position/speed or detect the rotor sector using hall signals and you want to apply filters to eliminate noise glitches? 

if so you can inspire by NXP S12ZVM motor control devkits schematics. But filter time constant (T=R*C) depends on signal you want to filter out :

https://www.nxp.com/design/development-boards/automotive-motor-control-solutions/magniv-and-s12-solu...

More recommendations regarding to hw design can be found here in application note AN5207. 

3-Phase BLDC Hall Sensor Application Using S12ZVM is described in AN4718. 

Best regards, 

Tomas Fedor. 

[jy1]

Hi Tomas

Thank you for your reply, I understand.

I also have another question, For this ADC circuit, how can I choose the resistance and the capacitance?

[tomasfedor]

Hi jy1, 

In my opinion those aspects needs to be taken into consideration: 

1) ADC input voltage limit : output of the voltage divider must not exceed allowed limit for ADC pin when maximum voltage appears on VBAT.

VBAT*R2/(R1+R2) < limit 

2) Acceptable power dissipation on voltage divider P=(VBAT^2)/(R1+R2) for your application.

3) R1, R2 and C will create a filter. Filter shouldn't distort useful signal (for example if VBAT ripple needs to be measured it shouldn't filter it)  or it shouldn't increase overvoltage detection time over what is acceptable for your application. 

4) Capacitor C will act as a supply for internal sampling circuit (internal resistance and sampling capacity). Energy will flow from C capacitor to sampling capacitor and it shouldn't create voltage drop that is out of acceptable value for your application. 

Characteristics of S12ZVL internal sampling circuit can be found in MC9S12ZVL Family Reference
Manual and Datasheet. 

Best regards, 

Tomas Fedor.

[lama]

Hi,

The question is application related and asked in vague way.

What? Where? Circuitry? Application?...PWM input signal to MCU to measure what?...PWM output signal from MCU to get what?

Best regards,

Ladislav

[jy1]

Hi,

The following picture is the application about the pwm signal to MCU