TMS570LS3137: Hercules ADC issue

Yunus Karaborek

Part Number: TMS570LS3137
Other Parts Discussed in Thread: HALCOGEN

Dear Team

One of my customer is working on TMS570LS3137 and want to use ADC of this MCU. In the datasheet ,They are using the voltage divider to measure the voltage. The current on the voltage divider is 200 microA, but they measure less than this value. it is mentioned that the leakage current is 4 microA, but they think that the leakage current would be around 150-200 microA. Could you please help to fix this issue? Is there any code example or any documentation which may help my customer to measure the voltage in the range of Hercules ADC?

Many thanks

Best Regards

Yunus

over 5 years ago

0 Miro over 5 years ago

TI__Mastermind 21425 points

Hello Yanus,

The formulas that are used for calculating the result are:

When calculating the exact value, reference voltages should be accurate in formula used in the code.

Another thing that has to be considered is sampling time. Increasing sampling time may solve this issue (default sampling time is 200ns). More about calculating actual sampling time can be found in the following application note:

Calibration procedure could be activated by the application as well. See at Section 19.8.1 in TRM.

APIs could be found in HALCoGen generated drivers.

Some guidelines for interfacing ADC could be found in:

Best regards,

Miro

0 Yunus Karaborek over 5 years ago in reply to Miro

TI__Expert 7450 points

Hi Miro

Thanks for the quick response. They are using 200k ohm high side and 10k ohm low side to divide 48 Volt, so the divided voltage is connected to the input of ADC. Could you please confirm if they exceeded the resistor value which is mentioned Rext 20k in the application note? Is there maximum value of this resistor? The formula is OK for them and it seems all is OK, but they are still having this issue.

Many thanks
Best Regards
Yunus

0 Miro over 5 years ago in reply to Yunus Karaborek

TI__Mastermind 21425 points

Hello Yanus,
Are they using external capacitor? Did you mean Rsource while mentioning Rext? Did they increase sampling time?

Best regards,
Miro

0 Yunus Karaborek over 5 years ago in reply to Miro

TI__Expert 7450 points

Hi Miro

They are not using external cap but they are using external resistor Rext

Could you please check again?

Best Regards

0 Miro over 5 years ago in reply to Yunus Karaborek

TI__Mastermind 21425 points

Hi Yanus,
What I suggest is connecting capacitor of 1uF at the ADC input and increase the sampling time. Connecting external capacitor will lower the needed time for ADC Csamp to settle.

Best regards,
Miro

0 Miro over 5 years ago in reply to Miro

TI__Mastermind 21425 points

Hi Yanus,
Did your customer make changes I suggest?

Best regards,
Miro

0 Yunus Karaborek over 5 years ago in reply to Miro

TI__Expert 7450 points

Hi Miro

They told me that their resistor value is the multiplier of 100K Ohm, so they can’t use 1 uf capacitor, because RC factor should be lower than 0.001, so they can use 10Nf. Isn’t it?

Best Regards

Yunus

0 Yunus Karaborek over 5 years ago in reply to Yunus Karaborek

TI__Expert 7450 points

Hi Miro

The issue has been fixed with your recommendation

Many thanks

Best Regards

Yunus

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TMS570LS3137: Hercules ADC issue