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TPS61099: Optimize the design to reduce external resistor divider power consumption

Gabriel Xu
Intellectual 2145 points
Part Number: TPS61099

Hi teams

My customer used TPS61099 in a wireless sensor product that is powered from a battery.

In order to reduce the power consumption on the resistor, the customer wants to increase resistance value.

As I know very large resistance value for resistor divider will lead to thermal noise.

Below is my question:

1) What's the common resistance limitation for total upper and bottom resistor? Customer is using 1Mohm configuration, will it have some risk?

2) Do we have any other method to reduce this kind of power consumption?

3) Will a fix output voltage version device of TPS61099 could achieve less power consumption compare to the adjustable version?

Thanks in advance.

  • 0
    TI__Mastermind 21565 points

    Hi Gabriel：
    I thought the TPS61099 supply power for wireless sensor all time, right? What's the details spec about Vout, accuracy and Iq?

    For your questions:
    1. For the best accuracy, the current following through Rbot should be 100 times larger than FB pin leakage current. The Ifb_leakage is 10nA typical and 50nA max according to the datasheet.
    Changing Rbot towards a lower value increases the robustness against noise injection. Changing Rbot towards higher values reduces the FB divider current for achieving the highest efficiency at low load currents. Take Vout=5V as an example, 1-MΩ and 249-kΩ resistors could be selected. High accuracy resistors are recommended for better output voltage accuracy.

    2. If the device need to keep enable all time, I can't think of a better way.

    3. Generally speaking, the fixed voltage version will achieve less power consumption in many application.
    For TPS61099, I have no details parameter in hand. If the exact answer needed, the process to apply for data should take time to through the process.

    Best Regards
    Minqiu

  • 0 in reply to Minqiu Xie
    TI__Intellectual 2145 points
    Hi Minqiu
    Thanks for your reply. In datasheet,only one Ifb_LKG data is given. This parameter is about 10nA(typ) and 50nA(Max).
    But acoording to my understand, as the resistor divider is integrated inside the chip for fix output voltage version, the IFB_LKG for them should be much higher than the adjustable version with two external resistor divider. Do you have accurate data for fix output voltage version and adjustable version? Thanks.
  • 0 in reply to Gabriel Xu
    TI__Mastermind 21565 points
    Hi Gabriel:

    For fixed version, we have optimized design for quiescent usage. There is no external consumption outside socket for voltage monitor. You could find the iq in datasheet to check if it meet the requirement of customer.

    Best Regards
    Minqiu
  • 0 in reply to Minqiu Xie
    TI__Intellectual 2145 points
    Hi Minqiu
    Thanks for your comments.
    For iq data, they list Vin/Vout iq when the output is 12V. I wondering to know what does it mean for the iq(Vout)?
    When the converter switching without any load, the Vout should source current not sink current i suppose. But in DS it says "quitscent current flow into Vout pin". I am not sure what does it mean.
  • 0 in reply to Gabriel Xu
    TI__Mastermind 21565 points
    Hi Gabriel

    Please see"Figure 17. Functional Block Diagram". You will found many function block is connected with the Vout. And that's one of the reasons will it needs current.

    If it operate in normal mode, Iout=IL-Iinternal. When the socket stop switch, it have no capability to source the internal circuit and IL=0. So Iout=-Iinternal. It change to sink current from Vout pin.

    Best Regards,
    Minqiu
  • 0 in reply to Minqiu Xie
    TI__Intellectual 2145 points

    Hi Minqiu

    Thanks for your comment, it's very clear.