LAUNCHXL2-RM57L: Does ADC work with negative values?

Apurv Mishra

Intellectual 750 points

Part Number: LAUNCHXL2-RM57L

Hi!

I am using RM57Lx board. I need to read external analog signal through ADC. Does it take negative values as well?

over 6 years ago

0 Miro over 6 years ago

TI__Mastermind 21425 points

Hello,
According to Table 7-15:
Output conversion code is 00h to FFFh [00 for VAI ≤ ADREFLO; FFF for VAI ≥ ADREFHI]

According to Table 7-19:
A-to-D low-voltage reference source MIN is VSSAD
VAI, Analog input voltage is within ADREFLO and ADREFHI

According to Device Recommended Operating Conditions:
VSSAD min is -0.1 and max 0.1.

For measuring negative values you must shift the signal.

Best regards,
Miro

0 Apurv Mishra over 6 years ago in reply to Miro

Intellectual 750 points

HI, Miro!
How do we know/set ADREFLO and ADREFHI in RM57Lx Launchpad?
I want to measure voltage from a photodiode.

Thanks,
Apurv

0 Miro over 6 years ago in reply to Apurv Mishra

TI__Mastermind 21425 points

Hello,
According to schematic diagram of RM57Lx LaunchPad ADREFLO is connected to GND via jumper resistor R1. You can connect ADREFLO to different voltage level using connector J9 pin 38 after removing R1. ADREFHI by default is connected to +3V3 via jumper resistors R2 and R3. You can connect it to +5V very easy by removing R3 and populating R4. If you need voltage levels different than +3V3 and +5V you can use connector J9, pin 39 after removing R2. Please consider absolute maximum rating when choosing reference voltages.

Best regards,
Miro

0 Apurv Mishra over 6 years ago in reply to Miro

Intellectual 750 points

Thank you for the help.

0 Apurv Mishra over 6 years ago in reply to Miro

Intellectual 750 points

How do we shift the signal?

0 Miro over 6 years ago in reply to Apurv Mishra

TI__Mastermind 21425 points

Hello,
With adding DC component for example.
You can find many solutions on Internet that uses operational amplifier for that purpose.

Best regards,
Miro

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LAUNCHXL2-RM57L: Does ADC work with negative values?