ADP1763: Max capacitive load that ADP1763 can support

In our design, we are using a single ADP1763 to power a RF TRx IC. A 10uF is placed at the output of ADP1763.

The evaluation board of the RF TRx IC suggests a number of parallel caps to be added at the individual power pins of the TRx IC. Effectively, the output of the ADP1763 sees a capacitive load of about 1700uF. This number is arrived upon by adding the caps at the individual pins(multiple 220uFs and 10uF). Kindly note that some of them at connected through a ferrite bead.

Is there a restriction on the maximum capacitive load that ADP1763 can drive? Are there any other design concerns that you can foresee?

A quick response would be much appreciated :). 

Thanks,

Guha

  • 0
    •  Analog Employees 
    on Dec 27, 2018 3:15 AM

    Hi Guha,

    It is case to case basis. Stability may be a concern at very high output capacitance. A similar question was posted for ADP1765 a while ago that used LC filter with total 1mF of output capacitance. Result was still acceptable. In your case, you have to test in your application: PSRR, load transient response, Vout ripple.

  • 0
    •  Analog Employees 
    on Jan 3, 2019 4:59 PM in reply to Fil

    Hi Fil and Guha.

    There is no limit/restriction on the amount of external capacitance on the ADP1763, as long as you place at least ~10uF's of capacitance directly at the "VOUT" pin of the ADP1763. You want this minimum of ~10uF's capacitor/capacitance as physically close to the "VOUT" pin as possible, while minimizing any inductance (due to ferrite beads, PCB inductance, etc.) of this minimum capacitor at the "VOUT" pin. Then, any additional bulk capacitance beyond/after this minimum capacitor requirement, will not make the ADP1763 go unstable.

    Also, you will want to make sure that the addition of the ferrite beads (inductance) does not create any high-Q resonances that results in additional ringing on the load side of the ferrite bead/inductor that may impact system performance.

    See "Ferrite Bead Demystified" article:

    https://www.analog.com/en/analog-dialogue/articles/ferrite-beads-demystified.html

    Thanks.

    Brandon