No subject

Tue Oct 6 13:45:31 CEST 2009

- one of C3003 and C3008 is probably redundant

- B3001 doesn't seem to serve a real purpose either, assuming correct

- HP/SPKRVDD are fed by AVCC_CODEC, which is fed by CODEC_3V3, which is
  fed by LDO2. LDO2 has a maximum current of 50 mA. Joerg says we need
  at least ~150 mA.

  So that's a big problem. Thanks for catching it !

  GTA02 supplies the audio amp directly from VB, but since HP/SPKRVDD
  are limited to 3.6 V, we can't use VB (or VSYS) directly.

  Possible solutions:

  - feed HP/SPKRVDD from IO_3V3. Needs checking if we're still within
    our current budget for IO_3V3. Also, what happens if the output
    gets shorted during jack insertion/removal ? A drop or even
    shutdown of IO_3V3 would be fatal.

  - we could try to reorder the LDOs such that we use one with that
    limit for HP/SPKRVDD. It could still also supply AVDD (with proper
    separation of current paths.) However, it's not clear what the
    LDOs do if exposed to an overcurrent situation. I haven't found
    any indication of overcurrent behaviour for the LDOs (except for
    HCLDO) in the PMU manual.

  - add a diode or LDO to drop VB/VSYS to the acceptable range and
    add a switch to cut it if CODEC_3V3 is down. (Switch and LDO can
    be the same component.)

Oh, and did anyone notice that the audio amplifier is not powered in
GTA02 if running from USB with the battery removed ?

If we can confirm that the LDOs handle overcurrent gracefully, then I
think the reordering of LDOs looks like the most promising choice.
E.g., swap LDO2 (CODEC_3V3, 50 mA, off in Standby) and LDO4 (BT_3V2,
150 mA, 2.8V in Standby).

If they can't handle overcurrent, then we'd probably need an external
LDO with switch.

Opinions ?

- Werner

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