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ADS8864 Power Sequencing

Christof Reinarz
Prodigy 90 points
Other Parts Discussed in Thread: ADS8864, ADS7042

Hi, 

I am working on a design with and ADS8864. The analog section has some signal condition with a couple of amplifiers and a voltage reference with no shutdown pins. The problem is, I need to shut down the analog section for extensive periods of time while keeping the digital section powered. The options I can think of are:

a) Shut down the analog section including AVDD using a load switch but keep DVDD powered up. There is no information on power sequencing in the data sheet so I am not sure if this isn't going to damage the device. Also I am not sure if there will be increased leakage currents.

b) Shut down the analog section including AVDD and DVDD of the ADS8864 using a load switch. In this case the SPI lines would remain connected to the uP which will remain powered all the time.

c) Replace the OPAmps and voltage reference with similar ones but with shutdown.

Which one is the best solution and most importantly, which has the loses average current consumption?

Many thanks in  advance for your help.

Christof

  • 0
    TI__Expert 8620 points

    Hello Christof,

    ADS8864 only consumes a current 50nA (Typ value as per the datasheet) when it is acquisition phase(When CS is High). So only 50nA is going to be saved when AVDD of ADS8864 is removed when it is not converting. Regarding the consumption on DVDD supply of ADS8864, the current is mostly consumed when there is activity on SDO pin. During acquisition phase there is negligible consumption from DVDD supply.

    But the power could be saved by disconnecting AVDD supply from analog front end or using analog front end with shut down pin.

    Regards,

    Lokesh

  • 0 in reply to Lokesh Ghulyani
    TI__Expert 8620 points

    Hello Christof,

    I have made changes to the post above to make it clear. Please refer to the post below.

    I think you are planning to save power by disconnecting AVDD and DVDD supplies from ADS8864 when it is not converting the analog input. But ADS8864 only consumes a current 50nA from AVDD supply (Typ value as per the datasheet) when it is acquisition phase(After the conversion is over and before the start of next conversion). So only 50nA is going to be saved when AVDD of ADS8864 is removed when it is not converting. Regarding the consumption on DVDD supply of ADS8864, the current is mostly consumed when there is activity on SDO pin. There is negligible consumption from DVDD supply when there is no activity on SDO pin.

    But the power could be potentially saved by disconnecting AVDD supply from analog front end or using analog front end with shut down pin.

  • 0 in reply to Lokesh Ghulyani
    Prodigy 90 points

    Hello  Lokesh,

    thank you very much for your response. You have made it clear.

    Best regards,

    Christof

  • 0 in reply to Christof Reinarz
    TI__Expert 8620 points

    Hello Christof,


    Can you please share about the application where you are planning to use ADS8864?

    Thanks,

    Lokesh

  • 0 in reply to Lokesh Ghulyani
    Prodigy 90 points

    Hi Lokesh,

    sure, no problem! I am designing an industrial, battery powered, wireless sensor to measure some variable every 1 to 60 minutes. Design is split into two boards: one with a wireless module, the A/D converter, the voltage reference and the other one is a small front end board that can be exchanged depending on what needs to be measured (current, voltage, temperature or others). Since the sensor is in sleep mode most of the time, my primary concern is keeping the quiescent and leakage currents as low as possible. The sensors form a special type of tree network based on the IEE 802.15.4 protocol. Applications are primary for mining processes in remote locations.

    Best,

    Christof

  • 0 in reply to Christof Reinarz
    TI__Expert 8620 points

    Hello Christof,

    Thanks for the details, ADS8864 is an excellent choice for low power and small size 16 Bit SAR ADC.

    If you find a similar need for ultra low power and ultra small size 12 Bit SAR ADC, we have recently released ADS7042(http://www.ti.com/product/ADS7042 ). ADS7042 consumes only 690uW at full throiugh-put. It is available in 1.5x1.5 mm QFN package and does not require external reference.

    Regards,

    Lokesh.