MSP430G2553: ADC Problem and ADC internal resistance?

Chen yan-ting

Intellectual 965 points

Part Number: MSP430G2553

Hello Guys,

I want to measure the high voltage so i use Voltage dividing circuit and

read adc value but some problem is appear;

then in programe i use vcc for reference;

adc=ADC10MEM;

voltage 1 = adc*3.3/1023; (ADC measure Voltage)

voltage 2 = voltage 1 * (R2+R1)/R1 (VCC VOLTAGE)

it strange then value is not correctly to three-meter;

for emaple 30V -VCC then the result like picture;

note:adc value measure is Equivalent to three-meter

over 8 years ago

0 Jace H over 8 years ago

TI__Guru 56685 points

Hello,

The input resistance of the ADC for this part is given in the datasheet. For this part, we only give a typical value, no max or min. This specification can be found on the following table " 10-bit ADC, Power Supply and Input Conditions (MSP430G2x53 Only)"

0 Chen yan-ting over 8 years ago in reply to Jace H

Intellectual 965 points

i am see the tutorial for msp430g2xxx series the page552 write max ohm is 2k.ok this is not important

so if norman the resistance is 1k ohm then ,how can explain the voltage .

if vcc=30v then vcc x (R1//1K/(R2+(R1//1K)) = 30 *0.5K/13.5=1.111V then is not equ 1.89V or 2.1V

so where the three-meter measure then get 1.89V???????

0 Jace H over 8 years ago in reply to Chen yan-ting

TI__Guru 56685 points

Hello,

What is the value of the ADC result after measuring the voltage?

0 Chen yan-ting over 8 years ago in reply to Jace H

Intellectual 965 points

Because i used 3.3 ref by adc channel , so the value is 0~1023, so the value mean measure the adc channel value so i need to return the voltage ,so i mul the 3.3/1023 if r1 is 3.3 mean the adc is full then see my circuit the div voltage mean can measure the max voltage 0-35v if vcc×r1/r1+r2 ,the vaule is near 3.3v

0 Jace H over 8 years ago in reply to Chen yan-ting

TI__Guru 56685 points

Hello,

From my previous post i was asking what actual ADC codes were you pulling from the device when it was running.

The ADC internal resistance is only relevant while the ADC is sampling.

Also, what are the tolerances for your resistors?

0 Jace H over 8 years ago in reply to Jace H

TI__Guru 56685 points

Hello,

Have you been able to gather the requested information above? If no response soon, i'll assume you have resolved your issue and I will close this post.

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MSP430G2553: ADC Problem and ADC internal resistance?