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ADS1299: ADS1299 VCAP1 appear -1.1V , SPI doesn't work

Sang-min
Prodigy 30 points
Part Number: ADS1299

hi my name is sang - min

i am using adss1299 like above picture

but i don't know why my circuit doesn't work. 

first, my main resource is 5V and using LOD regulator make DVDD 3V, AVSS -2.5V, AVDD 2.5V

and i find Application information blcok diagram in datasheet 

in that diagram , when i insert power, and reset, wait VCAP1>1.1V.

but my circuit doesn't appear above 1.1V. jut -1.1V(minus)

so i don't know why..

please help me i am consider about this during over one month..

  • 0
    TI__Mastermind 38745 points
    Hello Sang-ming,

    When you measure VCAP1 as negative, are you measuring with respect to AVSS or ground? You should measure that voltage with respect to AVSS.

    Besides VCAP1, what else about the device is not working? Your START pin is floating which could prevent the device from ever starting conversions. You should either tie that pin low and use the START command to start conversions or tie the START pin high if you never plan on stopping conversions. Otherwise you can control the pin with your microcontroller.

    Regards,
    Brian