FS4500 power on reset issue with KEAZ128 MCU

[snaku_lee]

Hi,

I am using a FS4500 as a SBC for a KEA (KEAZ128) MCU, the FS4500's VCORE is connect to KEA's VDD, and FS4500's VCCA is connect to KEA's VDDA. I have a problem when I power on the FS4500, the Vcore and Vcca are not stable while power on reset, you can see the waveform in the attachment file.

This problem can be solve if I use FS4500 Vcore only to provide 5V for KEA's VDD and VDDA.

Does any one know why can't I give independent 5V to KEA from FS4500?

Thank you,

Snaku

[guoweisun]

Do you mean the power up sequence of MCU's VDD and VDDA take this issue?

[guoweisun]

Do you know the current consumption of KEA's VDDA? if only use the internal MOSFET VCCA of SBC can only support 100mA.

[snaku_lee]

Hi guoweisun,

There is almost zero load on the VCCA.

And when I use SBC's VDD only as the 5V source to power on the KEA MCU, we found the slew rate is different on the Vcore and Vcca.

You can see the waveform, the Vcca is fast than Vcore.
CH1:Vpre
CH2:Vaux
CH3:Vcca
CH4:Vcore

Thank you,

Snaku