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TPS7A7001: Stability of phase characteristics

T Kishi
Genius 4425 points
Part Number: TPS7A7001
Other Parts Discussed in Thread: TPS7A83A, TPS7A85A, TPS7A84A

Hi

My Customer has question.

Please check about Q1 and Q2.
Phase Margin = over 45 deg, Gain Margin = Over 10 dB can be secured
Phase Margin = over 45 deg, Gain Margin = Over 10 dB Is there some feedforward capacity?

〇Customer’s Condition #1
　Parts Number: TPS7A7001
　Vin=1.8V
　Vout=1.0V
　Iout=0 to 1.158A
　Ta= 0 to 70degC
　Output Capacitance=3895.4uF (Ceramic Caps=135.4uF, Tantalum Caps=3760uF)
　Output Capacitors
　Ceramic Caps
　　10uF：GRM21BB31A106KE18L（MURATA）x 8pcs
　　1uF：GRM155B31A105KE15D（MURATA）x 55pcs
　　0.1uF：GRM155R11A104KA01D（MURATA）x 4pcs
　Tantalum Caps
　　470uF：TEPSLV0E477(12)12R（NEC-TOKIN）x 8pcs

〇Customer’s Condition #2
　Parts Number: TPS7A7001
　Vin=2.5V
　Vout=1.8V
　Iout=0 to 0.16A
　Ta= 0 to 70degC
　Output Capacitance=433.8uF (Ceramic Caps=57.8uF, Tantalum Caps=376uF)
　Output Capacitors
　Ceramic Caps
　　4.7uF：GRM32DB11E475MA61L（MURATA）x 8pcs
　　10uF：GRM21BB31A106KE18L（MURATA）x 1pcs
　　1uF：GRM155B31A105KE15D（MURATA）x 8pcs
　　0.1uF：GRM155R11A104KA01D（MURATA）x 22pcs
　Tantalum Caps
　　47uF：TEESVC1C476M12R（NEC-TOKIN）x 8pcs

Regard

T Kishi

  • 0
    TI__Guru 55940 points

    Hi T Kishi,

    The maximum output capacitance for TPS7A7001 is 200 uF.

    Please consider TPS7A83A if higher output capacitance is required.  Another option to consider is to place some of the bulk output capacitance on the input of the LDO instead.  This will help the LDO startup faster (it does not need to charge as much capacitance) and you will still have the benefit of the filtering provided by the capacitance.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Genius 4425 points
    Hi
    Thank you for reply.

    Does TPA7A7001 have the possibility of oscillation etc. when used in customer's condition?
    In other words, is there no way to have "Phase Margin = over 45 deg, Gain Margin = Over 10 dB"?

    Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Guru 55940 points
    Hi T Kishi,

    TPS7A7001 will not be stable with that large of an output capacitor. The datasheet limit of 200 uF is the limit for output capacitance. TPS7A83A is an alternative LDO that is better suited for applications with high output capacitance. You may also want to consider the higher current versions of TPS7A83A, TPS7A84A (3 A) or TPS7A85A (4 A). These higher current LDOs will allow more current through the LDO at startup to charge the output capacitors while maintaining the performance of the TPS7A83A.

    Very Respectfully,
    Ryan