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TPS61094: Issue with boost & buck mode of operation

Miteshkumar Dalabhai Patel
Intellectual 2130 points
Part Number: TPS61094

Tool/software:

Hi..

One of my customer is evaluating TPS61094 for their project in which they have Li-SOCl2 (3.66V) battery as main source & super cap of 3.6V.

Case 1:-

Vin = 3.66V

Vout slected = 3.0V

Vcharge = 3.5V

Vsupercap = 3.3V

In this case supercap charging ok but as soon as transmission starts (on load side Vout) device enters into Boost mode as Vin source is limited by 22 Ohms  to protect the battery. In boost mode transmission lasts for about 10 seconds & then MCU enters into sleep mode for 2 Hours. Since Supercap energy is consumed it discharged till 3.1 to 3.2V but now device is not entering into buck mode & Vout remains same as Vsupercap which is not expected.

As per our understanding in this case is --> Super cap should charge up to the Set voltage till it not reaches its final value & as soon as transmission starts current (about 320mA) must be delievered by super cap & as soon as transmission ends device must enter into buck mode & super cap charging should start again.

Is our understanding incorrect?

Now when we discharged the super cap till 2.9V then charging starts as expected so our observation is when Vcap voltage is less than the Vout Set  - 100mV then battery starts charging.

Can you help? What is wrong with our configuration?

This behaviour is observed on EVM as well as on customer board.

Regards,

Mitesh

  • 0
    TI__Genius 9025 points

    Hi Mitesh,

    In Boost mode, the VOUT is set at 3.0V, then when VSUP is higher than 3.0V, the Boost converter is operated in pass-through mode, which means the high-side FET is turned on.

    When TPS61094 operates in pass-through in Boost mode, it will not exit this mode until VSUP is lower than VOUT_target - 100mV, so that is why you find the supercap is charged again when VSUP is 2.9V.

    Customer could set the VOUT higher than VSUP-100mV, that is 3.5V, then it should ok.

    Regards,

    Nathan