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ADS1261: Design rules for PCB

Ka Chun Tsang
Prodigy 30 points
Part Number: ADS1261
Other Parts Discussed in Thread: ADS124S08, ADS124S06, LM27762,

Hello TI team,

I want to use the ads1261 for my new project. The datasheet is stating that AVDD minimum supply voltage should be 4.75V, but is it possible to supply the AVDD with 3.6V? If i look at the "Power-Up Characteristics" figure the minimum threshold for operation is 3.5V for AVDD-AVSS.

Regards,

Ka Chun Tsang

  • 0
    TI__Mastermind 44680 points

    Hi Ka Chun Tsang,

    Welcome to the TI E2E forums!

    Unfortunately, the ADS1261 is not designed to operated with an AVDD supply lower than 4.75 V. Meeting the minimum 4.75 V AVDD supply voltage in the "Recommended Operating Conditions" table is very important. Outside of this range, the ADC is not guaranteed to operate or perform according to the specifications in the "Electrical Characteristics" table. 

    The 3.5 V typical threshold is an internal threshold which holds the device in a reset state until this threshold is exceeding. Being a typical value, it is possible that 3.6 V many not always be sufficient to exceed this threshold.

    If you're looking for high-resolution Delta-Sigma ADC with a lower supply voltage, there are many other options that I would recommend, depending on your application. If you need a higher channel count ADC, such as the ADS1261, then I would recommend looking into the ADS124S08. The minimum AVDD supply on that device is 2.7 V.

  • 0 in reply to Christopher Hall
    Prodigy 30 points

    Hi Chris,

    Thank you for the fast reply.

    I am looking for a high resolution and high precision ADC with low noise and low drift with at least 4 channels. The operating voltage of my circuit would be 3.6V. Do you have any recommendation?

    Best regards,

    Ka Chun Tsang

  • 0 in reply to Ka Chun Tsang
    TI__Mastermind 44680 points

    Hi Ka Chun Tsang,

    Yes, since you originally were asking about the ADS1261, I think the ADS124S0x devices are probably the most comparable. There is a 12-channel version (ADS124S08) and a 6-channel version (ADS124S06).

    I would recommend taking a look at the ADS124S06.

    Let us know if you have any other requirements and we can help determine if there is another device more suitable for your application.

  • 0 in reply to Christopher Hall
    Prodigy 30 points

    Hello Chris,

    Thank you for the suggestion, i will try the  ADS124S06 for my project.

    I do have some questions, i noticed the noise performance of the ADS1261 is better than the ADS124. 

    1. If a charge pump is added for the ADS1261, how would the performance be compared to the ADS124?
    2. What about the different voltage potentials?

    Regards,

    Ka Chun

  • 0 in reply to Ka Chun Tsang
    TI__Mastermind 44680 points

    Hi Ka Chun,

    The ADS1261 is a lower-noise, but higher power consumption ADC. If you need the low-noise performance of the ADS1261 then you'll probably need to generate the 5V supply in your system. I'm not aware of any comparable ADCs that achieve the same level of noise performance with a lower analog supply voltage.

    If you create a clean 5V analog supply, then you should be able to achieve noise performance close to the noise specifications in the ADS1261 datasheet. To remove the switching noise from the boosted power supply, I'd recommend boosting the 3.6V supply to 5.5V, for example, and then using an LDO to generate the 5V supply. If you're okay with having a bipolar +/- 2.5V analog supply, then something like the LM27762 might be useful as it integrates a charge-pump + LDO. An example circuit for this device can be found on the ADS1261EVM (refer to the schematic near the end of the EVM User's Guide).

    The digital supply for the ADS1261 can be run off of 3.3V or 5V. The ADS1261's analog performance will be mostly the same except that the digital power consumption will be higher with a 5V supply. The digital supply voltage also sets the digital logic levels, so I'd recommend using the same supply voltage as your MCU to avoid having to use a level-shifter on the SPI bus.

    The ADS1261 is designed to work with different analog and digital supply voltages, but do take to care when laying out the circuit and try to utilize a common-ground plane to achieve the best noise performance. We have an FAQ with more details on this topic here: PCB Layout Guidelines and Grounding Recommendations for High-Resolution ADCs