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TPS629210: High consmption when Vin is below 3,8v

Mosfet
Prodigy 10 points
Part Number: TPS629210
Other Parts Discussed in Thread: TPS62160, TPS62125, TPS62840

Hi I've designed a ultra low power supply (see photo attached) to use it with a lithium battery that powers a sensor and MCU, it outputs 3,28v and everything is working fine at the end.

But when measuring consumptions with a Power Profiler Kit II and MCU not soldered I can see a really strange behavior.

When the Vin is between 3,2 and 3,4 the device consumption is 1,65mA, if I get next to 3,75 the consumptions rises to 3mA and when goes above 3,8v it drops down to 40uA which I believe is what's nominal.

Is there a way to fix that behavior?

Many thanks

  • 0
    TI__Genius 15327 points

    Hi,

    My colleague Athos will check your questions then reply you soon.

  • 0
    TI__Expert 7320 points

    Hi Lucas,

    I wonder if you have attached a wrong schematic since it's TPS62160 but not TPS629210. Which part do you actually use?

    Regarding the phenomenon, it's an normal performance of this device and all the converters with DCS control since its minimum off-time is triggered and no longer run at PFM/DCM but run into FCCM.

    • With some light loads that would be expected to operate in PFM mode, the pseudo minimum off-time allows the inductor current to go very negative

                    –This steals energy from the output caps and reduces the output voltage

                    –Once the low side FET is turned off, the output voltage is below the setpoint and a switching pulse must start again

                    –Result is forced PWM mode operation at duty cycles above ~90% and some loads

    Thus the min off-time performance results in higher light load input current at high duty cycles. It can't be fixed/solved. You can just try to increase the efficiency partly by increase the inductance.

    If you want to confirm this performance, you can test the waveform of SW pin and see whether its continuous or not at the 3.75Vin boundary.

    And at 3.2~3.4V, it runs into 100% duty cycle operation and the input current is lower.

    Please let me know if you have further questions.

    Athos

  • 0 in reply to Athos Zhao
    Prodigy 10 points

    I'm sorry, I'm talking about the TPS62160.

    I can see where the consumption comes, I took a closer look to the datasheet and I've seen that quote.

     When VIN decreases to typically 15% above VOUT, the TPS6216x does not enter power save mode, regardless of
    the load current. The device maintains output regulation in PWM mode

    I'm still learning about DCS behavior but using an over simplified explanation would be that this regulators does not fit my application because the battery goes as lower than 3.7v it wont be able to provide the 3.3v that I need maintaining the ultra lower consumption.

    That makes me wonder, what regulator would you suggest for my application? It's basically a sensor+MCU+LoRa radio, that runs on a 1 cell 3.7v battery.

    Many thanks for you help. 

  • 0 in reply to Mosfet
    TI__Expert 7320 points

    Hi Lucas,

    Yes, you are right. This part is not suitable for your application. 

    I just found TPS62125 which doesn't have this feature since it use PMOS for its High-side MOSFET.

    I had a bench test and the result shows that the input current of TPS62125 is ~20uA when Vin is between 3.3V~4V and ~200uA when Vin is under 3.3V.

    Does this consumption fit your application?

  • 0 in reply to Athos Zhao
    Prodigy 10 points

    Hi Athos, 

    TPS62125 looks really nice, I have to specially thank you for testing it on the bench, many thanks!.

    I have been doing some research and I also found out the TPS62840, I have been comparing both datasheets (suggested TPS62125 vs TPS62840) and as far as I can tell the TPS62840 has slightly better specs on Iq and RDS_On while 100% mode, that I believe would translate to longer battery life. 
    But to be hones I'm not confident enough to trust my lecture so I'd like to ask you if you can have a quick check to the TPS62840 and see if that will fit my application.

    Once again, many thanks!

  • 0 in reply to Mosfet
    TI__Expert 7320 points

    Hi Lucas,

    Our LVB team will support you about the TPS62840.

  • 0 in reply to Athos Zhao
    TI__Genius 16470 points

    Hello User,

    Thank you for using E2E,

    TPS62840 has the lowest Iq and has a very good efficiency at lighter loads, What kind of information would you like to know regarding TPS62840?

    Thank you & regards,

    Moheddin.

  • +1 in reply to Moheddin Pasha Shaik
    Prodigy 10 points

    Hi Moheddin,

    My main concern is if it would be able to maintain ultra low power consumption even if the Vin is really close to Vout, in my previous attempt with the TPS62160 I wast getting high consumption when Vin was 3.7v and Vout was set to 3.3v.

    Many thanks!

  • +1 in reply to Mosfet
    TI__Genius 16470 points

    Hello User,

    Thank you for the information, can you please provide me your operating conditions such as, typical load and maximum load. 

    Based upon your load current you can estimate the input current by using the efficiency curves as shown below.

    Thank you & regards,

    Moheddin.

  • 0 in reply to Moheddin Pasha Shaik
    Prodigy 10 points

    Hi Moheddin.
    Maximum load is about 150-200mA and typical load goes from 100uA to 600uA, I have set a Vout of 3.2v and the supply is from a one cell lithium battery.

    Many thanks!

  • +1 in reply to Mosfet
    TI__Genius 16470 points

    Hello User,

    Thanks for providing the operating condition.

    If I consider a use case of Vin = 3.6V, Vout = 3.3V, at 100uA the efficiency is approx. 88%

    Based upon efficiency data with the above conditions the current drawn by the device at 100uA load will be around  105uA.

    Thank you & regards,

    Moheddin.

  • 0 in reply to Moheddin Pasha Shaik
    TI__Genius 16470 points

    Hello User,

    If you don't have any further questions, can you please close the thread by clicking on resolved.

    Thank you & regards,

    Moheddin.