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TPS610985EVM-782: TPS610985

Nimesh Kotak
Prodigy 80 points
Part Number: TPS610985EVM-782
Other Parts Discussed in Thread: TPS610985, TPS61098, TPS610987

Hello there,

We have a power source which gives 1.5V at approx 20-30uA current. We want to regulate this supply to 1.8V so we are considering using TPS61098X device in low power mode.

We are doing some testing with TPS610985 EVM, but we are not able to get 3.0V at VMAIN node in Low Power mode, in no load condition. The VMAIN node goes up-to 1.3-1.4 V and starts dropping the voltage again. The input voltage is observed to be 0.42 V and VMAIN is settled at 0.4V in this case. 

What is the start-up power/current requirement for the chipset?

We will never use the device in active mode, in that case is it better to consider TPS61098 and TPS610987 for our application which has VMAIN=2.2V in Low Power Mode?

What can be the maximum value of series resistor for VIN pin and  maximum value of pull-down resistor for MODE pin?

Thanks,

Nimesh

  • 0
    TI__Mastermind 21565 points

    Hi Nimesh:

    Please check the setup. I wonder if the power supply has enough capability for it startup. It need some more current to charge the Cout during startup, and it may make power supply drop a lot if it doesn't have enough current capability.

    Besides, I wonder TPS610985 only regulate 3V. so how will you get 1.8V?  

  • 0 in reply to Minqiu Xie
    Prodigy 80 points

    Hello Minqiu,

    What can be the maximum value of series resistor for VIN pin and  maximum value of pull-down resistor for MODE pin?

    Can you please give the exact value of startup current if VIN is 1V?

    Our device needs minimum 1.8V we can make it works at 3V also. TPS61098X is the best we could identify. 

    And we have got our circuit working with other boost regulator from other company which has almost the same specs. We are trying to make it work with TPS61098X. 

    Do you recommend to add extra capacitance at Input or output node in the EVM? 

    Thanks,

    Nimesh

  • 0 in reply to Nimesh Kotak
    TI__Mastermind 21565 points

    Hi Nimesh:

    There is no exact value of resistance for Vin or Mode pin. You could check with the leakage or quiescent current of Vin pin.

    For Vin, (Vinput-Vin_min)>Iinq_Max *Rin. While, Vin_min=0.7V, Iinq_max=4uA. Similar calculation for mode pin.

    For the startup current, we have no exact value, as it will changed with different inductance, capacitance, and tolerance, and so on. You could test it on EVM to get a typical value  for reference. 

    Larger input capacitance could make the inrush current be smooth. While decrease the output capacitance will do some help to reduce the inrush current. But please check the Vout ripple and stable requirements. 

  • 0 in reply to Minqiu Xie
    Prodigy 80 points

    Hello Minqiu,

    We have been doing some testing with the TPS610985 EVM and observed that in no load condition the device takes 20mA for 100ms during startup with initial spike of 37.4 mA.(VIN=1V, VOUT=VMAIN=3V, Low Power Mode) This is in no-load condition, please refer attached image. Is this observation correct? How can we reduce the start-up current?

    Thanks,

    Nimesh

  • 0 in reply to Nimesh Kotak
    TI__Mastermind 21565 points

    HI Nimesh:

    It's normal for startup, as it need to charge the output capacitance even there is no load. Enlarge the value of the Cin, and decrease the value of inductance, Cout may do some help. But take care about the loop stable and ripple.

    Why do you want to reduce it? As the spike of 37.4mA is small enough for general application. 

  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points

    Hi Nimesh:

    As long time not hear you, I assume you have solved the issue. I'll close this post.

    If not, just reply below. Thank you~