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TPS61288EVM-064: Is TPS61288 suitable for Vin = 2.7-4.2V, Vout =12V/2A ?

Yeh Huar Kek
Prodigy 10 points
Part Number: TPS61288EVM-064
Other Parts Discussed in Thread: TPS61288

Hi expert,

I am trying to adjust to apply the TPS61228 for a single cell battery input to work between 2.7V to 4.2V, and Vout around 12V.

I have got a TPS61288EVM-064, the default output is approx 12V when unloaded, but the output starts to become unstable when loading more than 1A

and used WeBench to generate a design.

The designed schematics gave a different value for Rc, Cc and Cp, and I have tried them on the EVM,

However the output of the EVM cannot support more than 1A with a 3.0V input.

an you give me some guidance where i might have missed out something important?

thanks!

-

  • 0
    TI__Mastermind 34201 points

    Hello Sir,

    May I know how did you run this bench test? Did you use a power supply or a single cell battery for this test?

    Please note that when the EVM is outputting 12V/1A, the EVM input current is more than 12W/3Vin/0.90= 4.4A. You need a thick enough input power cable to avoid big voltage drop. 

    Do you have the unstable waveform to share with me? Like SW pin, Vin pin, Vout pin. Thank you.

  • 0
    Prodigy 10 points

    Hi Zack,

    Thanks for responding. 

    For the setup, I am using a DC power supply with 5A sourcing capability.

    The connecting wires is approx 30cm, AWG-22. With your advice, i now put 2xAWG-22 wires for both the Vin+ and Vin-

    I have restored the EVM board back to its original configuration and captured these waveforms.

  • 0 in reply to Yeh Huar Kek
    Prodigy 10 points

    This is with 3.8V input set at the DC power supply.

    So probably a 0.2V drop along the cables to the EVM board

    In this case the output of the EVM is connected to a 12ohm resistive load, and the output voltage 12.6V. (load current approx 1A)

    This is the waveform captured for a 10ohm resistor load (approx 1.2A)

    This is the waveform captured when the output of the EVM board is connected to a 8ohms resistive load. (load current approx 1.57A)

    It seems that somehow the Vin dipped below 2.7V.

    So my target application is to be able to drive up to 2A load current @12V, with a single cell battery.

    Can you help me understand where i can make improvements?

    thanks!

  • +1 in reply to Yeh Huar Kek
    TI__Mastermind 34201 points

    Hello Yeh,

    Thank you for the update and waveforms.

    I'm afraid your DC power supply current capability is not high enough. 

    With a 8ohm resistive load and load current is 12.9V/8=1.61A. Assume efficiency is 90%, VIN = 3.5V, the boost circuit input current is 12.9V*1.61A/3.5Vin/0.9=6.59A. 

    Therefore, the 6.59A triggers DC power supply current limit and DC supply voltage drops. TPS61288 input voltage is less than Vin UVLO and stops switching. 

    Please use a > 10A current capability DC  power supply and try again. 

  • 0 in reply to Zack Liu
    Prodigy 10 points

    Hi Zack,

    Thanks for the calculations, I have tried increasing the DC power supply current sourcing capability to 8A and can get the output stable with the above. So in terms of actual application, it looks like it is crucial to ensure the input supply impedance to the TPS61288 is low, otherwise under heavy currents, the voltage dip can cause issues.

    So If Vout=12V, and peak load current=2A,

    with Vin (min)=3.0V, and assuming 90% efficiency, the input source capability > 12*2 / 3 / 0.9 = 8.9A

    assuming droop margin of 0.3V, the impedance < 33milli-ohms.

    thanks again for your kind pointers.

    Please help me review if the above are correct.

    Best regards,

    Kek

  • +1 in reply to Yeh Huar Kek
    TI__Mastermind 34201 points

    Hi Kek,

    Glad to hear the news.

    Your calculation is correct. Please note that TPS61288 input UVLO falling threshold is 2V maximum, which could be found in EC table.

  • 0 in reply to Zack Liu
    Prodigy 10 points

    Thanks Zack!

    about the UVLO, this is a good reminder. thanks a lot.

    Have a nice day!