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LMR33610: LMR33610

user744376
Intellectual 420 points
Part Number: LMR33610
Other Parts Discussed in Thread: TPS61022, TPS62740

Hi,

I shall design a Power Back Up (PBU) function for 60s at 4W (5.1V 800mA) with super capacitors (charge time 180s)

General: Vin 12V to 34V.

I'm considering to use LMR33610 in two different ways. One to bridge the charge time second to charge the Super-cap:

1) Generate 5.1V 0.8A. (Generate 5.1V during the charge time for the super-cap).

After about 160s the TPS61022 starts and generate 5.2V in parallel with the above voltage.

Will this cause the LOW fet side in the LMR33610 to turn ON shorting the output or will the IC go into PFM mode both fets Off???

During the PBU time the voltage regulator has 5.2V at the output and 0V at the input.

In order not to backdrive voltage from the output back to the input rail I consider to place a diode in serial with the input voltage (pin 2) is this required?

Will there be drawn current back into the LMR33610 in this case?

2) Charging the super-caps.

I need to charge the super-cap from 0V to 4.6V with 0.8A.

Can you propose a simple (Low: comp. counts and low PCB arear and moderate cost) circuit that give the FB pin 5 a pre-bias regulating the output current to about 800mA +/- 5%?

FYI the above is related to #refid:d6cb966c-fedc-447d-adbb-413bd6a7936f

Br

Jørgen

  • 0
    TI__Mastermind 23815 points

    Hi,

    I hope i understand correctly your question. Let me know if the following answers are sufficient 

    1) As far as having a secondary supply in parallel with the LMR33610, it is recommended to put a diode OR at the output of the converter after the sense point of your feedback resistor divider. You can use this diode also to help preventing the discharge/reverse current from output back to the input voltage when the input is 0. 

    LMR33610 can startup with a prebias voltage, it means that if there is a voltage at the output at lower than the desired regulation voltage of the design, the LMR33610 should be able to ramp the output voltage up without shorting the output capacitor. If there is an overvoltage condition at the output of LMR33610, then both FETs will be turned off and the output will discharge to resistor feedback divider. 

    2) For charging super capacitor, maybe you can use something similar with this article

    http://www.ti.com/lit/an/slva678/slva678.pdf

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Intellectual 420 points

    Hi Arief,

    Thank you for fast reply.

    1) OK

    2) Charge of supercap

    Sorry the proposed solution will not work as TPS62740 not can charge with 0.8A and no MCU is available.

    We need to charge from Vin due to a supervision requirement.

  • 0 in reply to user744376
    TI__Mastermind 29480 points

    Hello,

    I am unsure that you will be able to find single chip solution for charging of super cap under your requirements.

    I would suggest researching available options on Ti.com, or following proposed solution in the appnote shared by Arief. 

  • 0 in reply to Marshall_Beck
    Intellectual 420 points

    Hi

    My original question regarding charging of the supercaps was:

    2) Charging the super-caps.

    I need to charge the super-cap from 0V to 4.6V with 0.8A.

    Can you propose a simple (Low: comp. counts and low PCB arear and moderate cost) circuit that give the FB pin 5 a pre-bias regulating the output current to about 800mA +/- 5%?

    Clerification of the above: in serial with the output of  the LMR33610 a small current sense shunt resistor could be placed.

    Do you have a proposal for a OPAMP that sens the current across the shunt resistor and tickel the FB signal of LMR33610 in order to have a constant current charging the supercaps until the voltage of 4.6V is reached?

    Br

    Jørgen

  • 0 in reply to user744376
    TI__Mastermind 23815 points

    Hi,

    Maybe you can use this opamp for the current sense amplifier

    http://www.ti.com/product/INA199

    The idea is to sense the output current and adjust the FB node accordingly. 

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Intellectual 420 points

    Hi Arif,

    Thank you this was what I was looking for

    Regards

    Jørgen