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TPS61099: Instability with source resistance and dynamic load

Dylan Maisel
Prodigy 20 points
Part Number: TPS61099

We are doing research for a customer who wants to optimize the TPS61099 boost regulator with a single rechargable 1.8V battery with source impedance ranging from 8-18 OHMS, depending on state-of-charge.

The load is a BLE radio, which spikes at 22 mA every 100ms. Quiescent current is about 2mA. The Radio's input voltage is 1.95V, regulated, we are using a 950K resistor for R1 and a 1M resistor to bring the output down to 1.95V. If we use a 1.8V DC supply with low source impedance, the system is stable. If we increase the source resistance over 5 OHMS, we cannot get stable startup. We see massive oscillations at both the input and output of the regulator. We are using 30uF input capacitance, a 2.2uH inductor, and about 20uF of output capacitance. We have tried different inductor values, low DCR, and no luck.

How can we adjust the circuit in order to minimize the oscillations in the feedback loop?

Thanks and best regards!

  • 0
    TI__Mastermind 46905 points

    Hi Dylan,

    it is not stability issue.

    during the startup, the TPS61099 relative large current to charge the output capacitor. however, the source can't support such current. that is why such behavior happens.

    please try to decrease the output capacitor to 2.2uF and increase the input capacitor to 20uF.  also don't connect the EN of the device directly to the input, but add a RC circuit to delay the startup of the IC before the input voltage is ready.