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# ADS1255: how to enable single conversion for the adc sampling chip of ads1255?

Part Number: ADS1255

Hello everyone, how to enable single conversion for the adc sampling chip of ads1255? What is the process for enabling a single conversion?
The circuit design I used is as follows:
pga=1,
Open the buffer,
ain0 is a single-ended input, ain1 is left floating
Aincom is connected to 2.5v,

differential reference voltage = 2.5v (will this voltage be amplified to 5v inside the chip? In this way, the internal reference voltage is actually 5v, and the software should use 5v as the reference voltage when calculating, right?)
SYNC/PDWN and reset are connected to MCU,
Excuse me, how can I starat a a single conversion?

thanks a lot!

• Hi Ming,

Some comments for your design:

• Please review the command definitions given in Table 24 in the datasheet. This will tell you which commands are required to read data, etc. Figure 18 shows the communication scheme and timing for your first conversion
• AIN0 needs to be measured against AIN1 or AINCOM using the ADS1255. So if AIN1 is floating and AINCOM = 2.5V, you cannot take a single-ended (ground-referenced) measurement
• Table 16 in the datasheet shows how the ADC's output codes translate to the input voltage using the binary twos-complement coding scheme:
• The positive full-scale code (7FFFFFh) corresponds to +2*VREF / PGA = 2 * 2.5 / 1 = 5 V for your case. Note that 5V is the differential input voltage, AINP - AINN. In this case, AINP = 5V and AINN = 0V for example
• The negative full-scale code (800000h) corresponds to -2*VREF / PGA = -2 * 2.5 / 1 = -5 V for your case. Note that -5V is the differential input voltage, AINP - AINN. In this case, AINP = 0V and AINN = 5V for example
• This is how you should interpret the codes you receive from the ADC

Please review this information and let me know if you have any additional questions.

-Bryan

• Hello, it is mentioned in the data sheet:
When using ADS1255/6 for single-ended measurements,
it is important to note that common input AINCOM does not
need to be tied to ground. For example, AINCOM can be
tied to a midpoint reference such as +2.5V or even AVDD

• So, how should the external circuit be designed?

• Is the command I use the single conversion mode like this: sync, wakeup, rdata, standby,

• Hi Ming,

My apologies, we generally only consider a single-ended measurement as one that is referenced to ground. The measurement you are describing where AINCOM = 2.5V would be considered "pseudo-differential". So that is just confusion on my end, as our nomenclature has shifted over the years.

-Bryan

• thank you very much

• So, for a single conversion, is the order of SYNC-> WAKEUP-> RDATA->STANDBY  correct?

• Hi Ming,

Yes, this sequence is correct.

You can also use the SYNC pin on the ADC for a similar purpose.

-Bryan

• thank you very much!!

• Hello, may I ask, under normal circumstances, what size of sps is better for configuration? Is 1000sps okay? I use 2000sps and found that every time the sampling interval is 10us, and the sampling is 20 times, there will be 1-2mv fluctuations.
Thank you

• Hi Ming,

You should be able to get correct data out regardless of which data rate you choose.

Can you explain more about what is going on with your system? And since this seems like a different issue than the one we discussed in this e2e post, can you please start a new post and I will respond there?

Thanks!