S32KのトピックRe: Query regarding impact on AFE if AFE VBAT_PWR pin filter capacitance changed

Query regarding impact on AFE if AFE VBAT_PWR pin filter capacitance changed

varunbharti — Mon, 30 Jun 2025 10:15:58 GMT

Hi,

I am using MC33774A for our LV BMS application for two-wheelers and three-wheelers. Due to system interference, we are experiencing a 2-usec dip on VBAT_PWR, which is causing the AFE to reset. (I have attached the recommended schematic and oscilloscope snip for reference)

To solve this issue, we want to decrease the cutoff frequency of the RC filter on VBAT_PWR by increasing the value of Cpwr to 0.47uF from 0.1uF.

In the datasheet, it is mentioned not to change the Cpwr value, but we don't see any impact on increasing the value.

Can anyone please verify and list the impact of increasing the value of Cpwr from 0.1uF to 0.47uF

Re: Query regarding impact on AFE if AFE VBAT_PWR pin filter capacitance changed

TomasVaverka — Tue, 01 Jul 2025 10:27:54 GMT

Hi,

This capacitor can be increased up to 4.7µF, see AN12963, section 5.4 - SM03 accuracy. Then 0.47µF is ok.

BRs, Tomas

Re: Query regarding impact on AFE if AFE VBAT_PWR pin filter capacitance changed

varunbharti — Tue, 01 Jul 2025 12:59:37 GMT

The AN12963 hardware guideline is recommended for MC33771x and MC33772x, but we are using MC33774A.

Re: Query regarding impact on AFE if AFE VBAT_PWR pin filter capacitance changed

TomasVaverka — Thu, 03 Jul 2025 11:38:15 GMT

Hi,

Please accept my apologies for this mistake, I will update this thread as soon as I have the answer for the MC33774A, still checking internally.

BRs, Tomas