what is the minimum saadc working freq,5us?

[wen]

i use the saadc as well as ble.the saadc dose not working on 200k hz(5us) as the Product Specification says.what is the wrong?

[Ole Bauck]

The SAADC can have acquisition time from 3us to 40us depending on the source resistance, see here. What is the configuration of your adc and what are you measuring? What is the source resistance? For which frequency does it work?

[wen]

thanks.I changed the acquisition time and it worked.But at the 200K and 100K sample freq,the wave was dithering.I looked at the timer again,found that the timer's freq is also dithering at 200K and 100K freq.Why?

[zhwzh308]

If your samples are dithering, it could be because you have too much impedance at the port. Is AIN attached to a high impedance circuit? the specification has some recommended impedance values, such as 3us less than 10k ohms, 5us less than 40k ohms.

[wen]

i test the timer itself,not including the saadc and the timer is dithering at 100K and 200K.

[zhwzh308]

I see, I assume you are using TIMER0 on the system? What IRQ do you use for TIMER0_CONFIG_IRQ_PRIORITY? Default is APP_IRQ_PRIORITY_LOW, have you tried anything higher?