LAUNCHXL-F28069M: Pull-down resistor for ADC

Kash Olia

Part Number: LAUNCHXL-F28069M

Hello,

Is it recommended to use external pull-down resistors when designing an application with ADC channels? Should an additional resistor used to limit the current?

Thanks,

over 5 years ago

0 Genatco over 5 years ago

Guru 55963 points

Pull down No - series yes but limited to RC charge sharing and desired settling times for charge sharing to be most effective.

0 Genatco over 5 years ago

Guru 55963 points

Only require pull down with series for a voltage divider if input voltage > ADC reference, often set to 3v3. If you have a +5v input it must be divided to keep it below the reference.

0 Kash Olia over 5 years ago in reply to Genatco

Genius 3215 points

GI,

The problem is they ADC channels reads random numbers when they are floating, that's why I thought pulling them down seems to be a good idea.

0 Genatco over 5 years ago in reply to Kash Olia

Guru 55963 points

Khashayar olia said:
The problem is they ADC channels reads random numbers when they are floating,

Don't configure channels util there is a wired connection present or you can drain the FIFO each loop if it must be configured. Open channels invite sources of EMI into the ADC.

0 Kash Olia over 5 years ago in reply to Genatco

Genius 3215 points

GI,

Can you share the document describing the settling time?

Thanks,

0 Genatco over 5 years ago in reply to Kash Olia

Guru 55963 points

/cfs-file/__key/communityserver-discussions-components-files/171/TI_2D00_Analog-ADC-source-impedance-spna118b.pdf

Best of luck on your experimenting!

0 Kash Olia over 5 years ago in reply to Genatco

Genius 3215 points

Thank you GI!

0 Genatco over 5 years ago in reply to Kash Olia

Guru 55963 points

Your welcome!

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LAUNCHXL-F28069M: Pull-down resistor for ADC