MSP430F67791A: MSP430F67791A SD24INPUT CURRENT

j.yamamoto

Hello.
I have connected SDxN0 and added voltage divided by R19 and R20 as shown in the attached circuit.
When I turn on the power supply, 12mA flows to SD_N, which causes a voltage drop.
I have 6 ports of SDxN0 connected and I think the current value is too high.
Or is it normal?
What would be the normal current value?
Thank you in advance.

AVCC=3.3V
VCC=3.3V
SD_N, SG_1, SG_2, SG_3, AD_REF,TP Measured voltage（0~3.3V) respectively
VASYS1 and VASYS2: Connection
VDSYS1 and VDSYS2: connection
AUXVCC1, AUXVCC2, AUXVCC3 = 3.3V
MCLK 16MHz

over 3 years ago

0 Luke Ledbetter over 3 years ago

TI__Mastermind 27250 points

Hello J Yamamoto,

I would expect less current going through R20 and R19, seeing as it is a voltage divider, I would be expecting 7.5mA. For the input it is higher than the typical differential input and you're probably running over the FSR of the ADC. Can you measure the voltage across R20? Also you could increase the value of those resistors to lower the current also.

I do see you're inputting the result of the voltage division of AVCC, R6 and R9, is this intentional?

Regards,

Luke

0 David Schultz over 3 years ago in reply to Luke Ledbetter

Guru 26305 points

Given that this one particular voltage divider has 12V on one leg, I would carefully inspect those resistors to verify their values. Forward biasing the clamping diode would result in excess current.

Not sure why an external and low accuracy reference for the ADC is being use.

0 j.yamamoto over 3 years ago

Prodigy 40 points

Sorry. This case has resolved itself.
There was a short in the SD_N line and another circuit that was drawing current.
Thank you very much for your advice.

0 j.yamamoto over 3 years ago in reply to Luke Ledbetter

Prodigy 40 points

Thanks for the advice.

The voltage divider between R6 and R9 is intentionally put on.

0 j.yamamoto over 3 years ago in reply to David Schultz

Prodigy 40 points

Thanks for the advice.
It looks like I need to re-examine the ADC circuitry, etc.

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MSP430F67791A: MSP430F67791A SD24INPUT CURRENT