TAC5112EVM-K: Vdd of MEMS MIC(SPH8878LR5H-1) is lower than expected 3.3V

Hi Kawasaki-san,

The R45 on the EVM that is near the microphone is a 10kOhm series resistor. This could be the reason for the drop in the 3.3V supply to the microphone's Vdd pin.

We can bypass this resistance so that the VDD seen on the microphone is 3.3V.

Thanks and Regards,

Lakshmi Narasimhan

Hello Lakshmi-san,

Thank you for your comments.  I understand the issue is a common issue for all the EVMs.  Actually, they changed the PU resistor to 2.7kOhm to have VDD of U5 2.7V which is the minimum voltage for U5 to work, but I'll tell them bypassing R45.

Did you know the U5 doesn't work as it is due to the voltage drop of R45?  Would you pleaese tell me other known issues that you're aware of sof far?  If you have EVM errata, that's helpful for us.

Best Regards,

Yoshikazu Kawasaki

Hello Lakshmi-san,

Would you please tell me also the background of the R45?  Does the MEMS MIC(SPH8878LR5H-1) require that?  It's obvious that it drops the voltage depending on the power consumption of the device.  The EVM circuit is often referred to the customers for their actual applications and we FAEs also refer to it, so the circuit is expected to work well.

Best Regards,

Yoshikazu Kawasaki

Hi Kawasaki-san,

Based on the datasheet of the microphone (SPH8878LR5H-1), the typical operating supply voltage is 2.75V, and minimum voltage is 2.3V. Since the voltage at the Vdd pin of the microphone is dropping to ~2V with R45, it was below the minimum operating supply voltage. Bypassing the R45 ensured the microphone's supply voltage was within the 2.3-2.75-3.6 specification mentioned in the microphone datasheet.

Thanks and Regards,

Lakshmi Narasimhan

Hello Lakshmi-san,

Thank you very muich for your comments.  I'm wondering if there might be other issues on the EVM, the reason why you put the resistor of R45 and if you validated the EVM works well in your side.  Would you please give me your comments for these?

1. My customer is worried if it is the only issue on the EVM.  Would you please tell me if R45 is the only issue on EVM you're aware of so far?

2. If I look at the datasheet of the MEMS MIC(SPH8878LR5H-1), the typial applciation shows Zrf as shown below, so is it the reason why you put pull-up resistor of R45 on the EVM?

3. I suppose you would be able to find the MEMS MIC doesn't work once you validate it, but have you done that in your side?

Best Regards,

Yoshikazu Kawasaki

Hello Lakshmi-san,

I haven't received your reply yet, but I need to tell my customer for my questions I asked a week ago.  Would you please give me your comments?  If I still don't get your reply, I understand these are your comments.

1. R45 is the only issue that you're aware of so far.

2. The datasheet of the MEMS MIC(SPH8878LR5H-1) shows the pull-up resistor of Zrf, so you added R45.

3. You haven't validated if U5 works or not yet, but you've done rest of the others.

Best Regards,

Yoshikazu Kawasaki

Hello Lakshimi-san,

Thank you for your comments.  Please let me tell your comments to my customer.

Best regards,

Yoshikazu Kawasaki