广告C in differential mode

Hello Rony, i will have one of the team contact you. Our datasheet is a bit unclear when it comes to the ADC. Someone will be in touch shortly.

BR JE_Dialog

Hi Rony,
You are correct in that subtracting the output values from the single ended inputs should give the same result as the differential input. However you have to make sure to first make the conversion from the ADC value to the actual voltages. See the details shown below

GP_ADC_ATTN3X GP_ADC_SE Input channels Input scale Input limits
0 1 P0_0, P0_1, P0_2, P0_3 0 V to +1.2 V -0.1 V to +1.3 V
0 0 [P0_0, P0_1], [P0_2, P0_3] -1.2 V to +1.2 V -1.3 V to +1.3 V
1 1 P0_0, P0_1, P0_2, P0_3 0 V to +3.6 V -0.1 V to +3.45 V
1 0 [P0_0, P0_1], [P0_2, P0_3] -3.6 V to +3.6 V -3.45 V to +3.45 V

If this does not answer your question, can you show some of the values you read back from the ADC in both single ended and differential mode?
Best regards,
RvA (Dialog)

Hi Rony,

The table I put in the earlier post is a bit garbled. Here is a better picture:

Best regards,

RvA (Dialog)

Hi Rony,

Closing this topic for the moment as we discussed by mail that the differential ADC measurements need further documentation and we recommend to use single-ended ADC measurements for the moment.

Best regards, RvA(Dialog)

Hi,
About SDK5.0.3:

adc_init(0,GP_ADC_SIGN,0);
adc_usDelay(20);
adc_enable_channel (0);
adc_sample=adc_get_sample();

Shouldn't adc_sample be P0_1- P0_0 ?
Should the measuring range be [-1.2V, 1.2V] ?

It cannot measuring the correct value base on the above code.

Looking forward to your reply.
Thanks.

Hi z20121202038,

Depending on the channels that you would like to measure you will have to make the proper adjustments, as the datasheet indicates the GP_ADC_SEL should be 0000 if you would like to measure P00 vs P01, so make sure that the configuration is proper, also configure your pins to ADC functionallity with the GPIO_ConfigurePin. Other than that you can apply the calibration procedure with the below modification since you would like to use differential mode:

instead of:

new_adc_off_p = 0x200 - 2 * adc_off_p;
new_adc_off_n = 0x200 - 2 * adc_off_n;

replace the above with this:

new_adc_off_p = 0x200 - adc_off_p;
new_adc_off_n = 0x200 - adc_off_n;

Thanks MT_dialog

Hi MT_dialog,

I am encounter the problem with differential mode
1)
Connect P00 and P01 to ground.
Modify the calibration procedure as your advise.
But the output is 0x300 or 0xFF, why not 0?
2)
Is the output is a unsigned integer or signed integer ?
3)
Can you give me further documentation of it ?

Thanks.

Hi MT_dialog,

A detail test as follows:

/************************************************************************************/
uint32_t adc_value1=0;
uint32_t adc_value2=0;
uint32_t adc_value3=0;
uint32_t adc_value4=0;

uint32_t adc_get_vbat_sample(bool sample_vbat1v)
{
uint32_t adc_sample, adc_sample2;
uint32_t att = GP_ADC_ATTN3X;

adc_calibrate();
adc_init(GP_ADC_SE, GP_ADC_SIGN, att);
adc_usDelay(20);
adc_enable_channel(ADC_CHANNEL_P00);
adc_sample = adc_get_sample();
adc_value1 = adc_sample;
adc_usDelay(1);

adc_calibrate();
adc_init(GP_ADC_SE, GP_ADC_SIGN, att);
adc_usDelay(20);
adc_enable_channel(ADC_CHANNEL_P01);
adc_sample = adc_get_sample();
adc_value2 = adc_sample;
adc_usDelay(1);

adc_value3 = adc_value2 - adc_value1;

adc_calibrate();
adc_init(0, GP_ADC_SIGN, att);
adc_usDelay(20);
adc_enable_channel(0x0000);
adc_sample = adc_get_sample();
adc_value4 = adc_sample;
adc_usDelay(1);

adc_disable();

return adc_sample;
}

also, we configure the Pin as :
GPIO_ConfigurePin( 0,0, INPUT, PID_ADC, false );
GPIO_ConfigurePin( 0,1, INPUT, PID_ADC, false );
/************************************************************************************/

Result：
adc_value1=0;
adc_value2=0x390; // 3.206V
adc_value3=0x390;
adc_value4=0x02B; // 0.151V

Looking forward to your reply.
Thanks.

Hi z20121202038,

Unfortunatelly there is no documentation or an example how the to operate with the differential ADC, most of the customers are not using the differential but the single ended mode, when zero voltage is applied the output of the ADC should be close to 1FF which is half or the 10 bit range since you are measuring from -1.2V to 1.2V (or multiplied by 3 with the attenuator), the output of the ADC is an unsigned 10bit value. Also try not to use the GP_ADC_SIGN when initializing the module and using the differential mode.

Thanks MT_dialog