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TLV70225DBVT and TPS60401 together consume 100uA of no load current and no 2.5V regulation

Veeresh PS40
Prodigy 30 points
Other Parts Discussed in Thread: TPS60401, TLV702

Hi,

We are working on remote monitoring application using Zigbee and signal conditioning circuit for soil moisture and it is battery operated. 

We have chosen TLV70225DBVT  for generating 2.5V and TPS60401 for generating -2.5V to get dual supply for opamps LPV324M/NOPB. 

We have designed a power supply board ( with TLV70225DBVT and TPS60401). It is consuming a lot of current around 100uA at no load condition and voltage is not getting regulated. We are getting 3V when battery is 3.6V. Below is the schematic.

Is the LDO selection is appropriate and capacitor values are appropriate? Please suggest for improving the design. 

Thanks,
Precision-Farmers
Bangalore, India.

  • TI__Guru 55940 points

    If you remove the TPS60401, what does the output read? What is the current draw?

    Very respectfully,

    Ryan

  • in reply to Ryan Eslinger
    Prodigy 30 points
    Hi Ryan,
    Thanks for the reply.

    We are giving 3.3V input.

    If we remove TPS60401, the output read is 2.89 and it is consuming a current of 40uA.

    I am worried that it is not regulating to give 2.5V. Please suggest for improvement.

    Thanks,
    Precision-farmers
    Bangalore, India.
  • in reply to Veeresh PS40
    TI__Guru 55940 points
    Hi ,

    The with TPS60401 removed, is there any other circuitry on the output of the LDO? Is it possible to provide a scope shot with Vin and Vout for TLV702?

    Very Respectfully,
    Ryan
  • in reply to Ryan Eslinger
    Prodigy 30 points
    Hi Ryan,

    No circuitry was there when TPS60401 removed. Vout was 2.89 with 3.3V and it will increase if I increase the voltage.

    I am sorry, I do not have the scope shot waveform bot the waveform was good with acceptable ripple voltage.

    Is there a reference design? our application is to work with Zigbee. Circuit consumes a current of 45mA at transmission and 100uA at sleep.

    Please suggest to improve the circuit or a better regulator for this application with better cost.

    Thanks,
    Precision-farmers
    Bangalore, India.
  • in reply to Veeresh PS40
    TI__Guru 55940 points
    Hi ,

    It sounds like the LDO is not regulating; however, I do not see an issue with the provided schematic. The waveforms would go a long way in helping to debug the issue.

    Have you seen this on multiple boards? Have you tried replacing the TLV702 and powering it (with TPS60401 still removed)? If so, does it yield the same result?

    Very Respectfully,
    Ryan