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Ultra fast power switching with TPS62770

Sadok Bdiri
Prodigy 50 points
Other Parts Discussed in Thread: TPS62770, TPS62748, TPS62740

Hello everyone,

I have a device i need to power with 1.0 V. It's  sensitive to voltage supply variation. I'm concerned to use TPS62770 for this matter. According to the datasheet, the accuracy of Vout is -/+ 2.5% which very fine to me. However. My device is going to be power gated where Toff=4ms and Ton=4µs (D=0.1%) by controlling an SPDT put between the TPS62770 and my device . Now the transient behavior of the supply voltage TPS62770 is unclear to me in this situation. Given that my device will have some 100 ns inrush current. My question is how is TPS62770 going to maintain this voltage output (Step-down) accuracy in this situation? If I use the integrated step-up, lose the SPDT and use the EN2/PWM pin to perform the power gating. Then, Vout2 will be used and i will have to adjust the voltage by means of the voltage divider which can also be inaccurate. Please enlighten me.

Thank you,

  • 0
    TI__Intellectual 1110 points
    Hi Sadok,

    do you have a schematic to get a better understanding?
    What is the purpose of the power gating?

    Best regards,
    Felix
  • 0 in reply to Felix Risch25
    Prodigy 50 points
    Power gating is for power savings purposes. My device consumes relatively high and I need it active for short period of time. Afterwards I disconnect it from power supply to save energy. Because of its sensitivity to supply voltage variations. The transient response of the step-up/buck converter is important during the ton period of the device. Unfortunately, i don't have a schematic at the moment. But it's rather just 3 devices connected. The TPS62770 (step-down, Vout1)--SPDT--LOAD. Or TPS62770 (Step-up, Vout2)----LOAD and gating is done on EN2/PWM pin.
  • 0 in reply to Sadok Bdiri
    TI__Intellectual 1110 points
    Hi Sadok,

    the option to Enable / Disable the DCDC converter may not work, as during the off time the output capacitor gets discharged and then the softstart time of the converter is too slow for your application (5ms for the step-up and 1.2ms for the step-down).

    My recommendation is to keep the step-down converter enabled all the time. During Toff (disconnected by the SPDT), the quiescent current of the step down converter is very low. In case the load current of your Device is less than 100mA you can use the load switch of the TPS62770 (or TPS62740, TPS62748) to connect and disconnect the device during Toff. The behavior of the load switch is similar to the TPS62770 (see www.ti.com/.../tps62740.pdf Figure 43). As the load switch is connected to the output of the step down converter, the transient response should be similar.

    Best regards,
    Felix