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TRS3122E: Charge pump Capacitor

Lilian Chang
Intellectual 1555 points
Part Number: TRS3122E

Hi Team，

If my customer use charge pump caps C1/C2=200nf, C3 open, C4/C5=100nf.

 What's the result will be?  Anything will be impacted?

Thanks.

  • 0
    TI__Mastermind 48195 points
    Hi Lilian,

    The TRS3122E's charge pump can operate in Doubler Mode or Tripler Mode. When Vcc >2.9V, The device operates as a doubler using C1, C2 as flying caps and C4, C5 as reservoir caps to output +-5.4V. C3 is ignored in this case and C3+, C3- can be left open. When 1.65V < Vcc < 2.1V, the device acts as a tripler, using C1, C2, C3 as flying caps and C4, C5 as reservior caps to output +-2.65*Vcc. See section 8.3 on datasheet.

    Given these modes, the device will work as intended with no C3 as long as Vcc is with the specified range. Without C3, the device won't be able to properly charge the reservoir caps at lower supply voltages.

    Table 1 on the datasheet recommends C1, C2 to be 100nF when the supply is 3.0V- 3.6V for optimal performance. Using larger values for the flying caps could cause more noise on the output of the charge pump, but should still be able to charge the reservoir caps.

    Let me know if you have any more questions.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    TI__Intellectual 1555 points
    Hi Eric,

    Thanks for your answer.
    Table in mentioned condition of VCC=VL, but what if VCC=3.3V , VL=1.8V? Anything different ?
  • 0 in reply to Lilian Chang
    TI__Mastermind 48195 points
    Hi Lilian,

    This distinction is mostly important when VL > Vcc. In this case, ripples in the charge pump output could effect logic levels. In your case where VL < Vcc, this should not be a concern.

    Regards,
    Eric