RM57L843: ADC

VEERAPPAN P

Part Number: RM57L843

Hi team,

In our project we use RM57L843 Microcontroller I have some doubts on ADC.

When the ADC Channels are not connected to any inputs that means if the ADC channels are left free why different voltage is read by the controller?

Here I am giving 0v to 0th channel only other channels are left free but some voltage are present. why?

vrefh = 3.3v, vrefl = 0v.

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1262774/rm57l843-arm-based-microcontrollers-forum/4782589?tisearch=e2e-sitesearch&keymatch=%20user%3A554481#4782589

In this thread we discussed that 6th channel only not working in ADC. Now we replaced the controller, after that the 6th channel is worked and we soldered the 6th channel not working controller to our launchpad, In launchpad also that 6th channel is not working. can you please tell why that particular channel is not working.

Thanks

regards

Veerappan P.A

over 2 years ago

0 jagadish gundavarapu over 2 years ago

TI__Guru 70621 points

Hi Veerappan,

The unconnected channels are called floating input channels. This floating input pin is susceptible to electrical noise that makes the I/O randomly fluctuate between low and high. Such noise sources include thermal noise and EMI since the lead of the floating pin acts like tiny antenna.

Refer below thread for more details:
(8) TMS570LS0432: ADC function， What is the sampled value - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

(8) RM48L952: ADC stuck on busy - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

So, if there are any unused channels then we should either should not do conversion, or it should be connected to some reference voltage like VCC or GND.

In below thread they did a test on unconnected ADC channels by enabling the "Sampling Capacitor Discharge Mode"

(8) TMS570LC4357: How to test and verify the ADC converted data which is triggered by ETPWM? - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

And after doing that they got less than 100 value on unconnected channels, if you want you can try this mode:

VEERAPPAN P said:
In this thread we discussed that 6th channel only not working in ADC. Now we replaced the controller, after that the 6th channel is worked and we soldered the 6th channel not working controller to our launchpad, In launchpad also that 6th channel is not working. can you please tell why that particular channel is not working.

The corresponding channel might be damaged.

By any chance did you apply any voltage beyond the maximum rating voltage of ADC pin?

Sometimes touching the pin directly with hand will also causes the ESD damage for corresponding pin.

So, it is difficult to tell exact route cause for this failure.

Thanks & regards,
Jagadish.