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LM2735: Disabled mode power consumption

Alfonso Lorente
Prodigy 20 points
Part Number: LM2735
Other Parts Discussed in Thread: LMR62014, , TPS61040

Hello,

I am using the LM2735XMF to boost from 3.6V to 5V and 200mA  in a battery powered design which has to achieve around 10 uA in low power mode.

The problem I am facing is that I am seeing an extra 90 uA current consumption that I have realized is coming from the FB circuit of the converter through Rfbt(R2) & Rfbb (R1) resistors.

Is there an easy way to avoid this current from draining the battery by modifying the circuit? I tested incresing resistors value but then the converter didn't work properly, so I assume it has to remain with similar values to the suggested by Power Designer (R2 = 10k suggested by the datasheet).

If it is not possible can anyone suggest a device that could fit our requirements with a simillar package (SOT23)?

Thanks

  • 0
    TI__Genius 14185 points

    Hi Alfonso,

    It can be calculated that the current flow through R1 and R2 is 5V/ (30k+ 10k) = 125uA, just meet your test result.

    So, if you want to reduce the current, you can enlarge R1 and R2.

    The feedback input bias current is 1uA max, so you just need to ensure the current flow through R1 much more than it, so you can choose R1and R2 120k and 40k.(you can try larger)

    Also, it is necessary to change Cf according to R1, here we keep the zero the same frequency, 30k*1.8n=120k*Cf, so choose Cf=0.47nF.

    please check if the parameters meet you demand.

    Best Regards

    Fergus

  • 0 in reply to Fergus He
    Prodigy 20 points

    Great thanks, I will try it for now, but this power consumption would be still too high. Will try later implementing a switch to power ON/OFF the whole circuit.

    Kind regards

  • 0 in reply to Alfonso Lorente
    TI__Genius 14185 points

    Hi Alfonso,

    You can pull pin SHDN low to shut down the chip. When shutdown, output voltage will be same as input.

    The shutdown current will be 80nA. 

    Regards

    Fergus

  • 0 in reply to Fergus He
    Prodigy 20 points

    I do so, the problem is having this 3.6V in the output makes the battery drain around 90uA through L1->D1->Rfbt->Rfbb.

    Thanks, regards

  • 0 in reply to Alfonso Lorente
    TI__Genius 14185 points

    So, when R1 and R2 become larger like 120k and 40k, the current will reduce.

    As for the device that could fit our requirements with a similar package (SOT23), there are three kinds of choices for your reference.

    1. LMR62014, the chip gets a Quiescent Current of 2mA (switching) and current limit of 2A.

    this is most close to LM2735 (Quiescent Current of 7mA and current limit of 2.25A)

    2. TPS61040, the chip gets a Quiescent Current of 28uA (switching) and current limit of 400mA.

     For 3.3 to 5V/200mA, it could be just fit the spec but with no more margin.

    3.TPS613222A, the chip gets a Quiescent Current of 6uA (switching) and current limit of 1.8A.

    the disadvantage is that it is not pin to pin with lm2735, but the circuit much smaller with less outside components.

    Best Regards

    Fergus