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Original question:

TPS22933: Pins interchangeable?

TPS22933: Add / mux a second output

Chris Schramm
Intellectual 590 points
Part Number: TPS22933
Other Parts Discussed in Thread: BQ24040, SN74AUP1G80

Apologies for my 3rd post concerning TPS22933 ;) I really like this IC but its 3V6 Out brings some challenges...

Alright. Design background: our MCU takes 3.3V, so for lowest power it should be possible to input 3V3 directly, sort of bypassing TPS22933.

There are four power supplies: 3V3 (as discussed), VIN, VBAT and VUSB.

Output rails:
Any rail except 3V3 is powering BQ24040 and charging a small battery (VCHRG in schematic).
VOUT is switched 3V6 dropped via Schottky Diode to about 3.3V and finally feeds 3V3 rail

Well, I guess by now the "circular reference" is already clear: the TPS22933 should only be enabled if 3V3 is absent - but because TPS22933 itself is generating 3V3, that's a problem which can not be fixed with a simple logic inverter (EN = !3V3).

I thought of another power mux, but they will all bringt additional power consumption even if 3V3 is the only source (and additional 10uA would hurt)

So now I'm having a D FF in mind (SN74AUP1G80):

But I wonder if I can directly connect CLK to VCC. Will the gate see it as a rising edge? Or should I add a 100nF cap or so to create a delay?

Two additional "bonus questions":

- Is any of TPS22933's outputs reverse current protected?

- If the battery is the only (or highest-voltage) source, are problems to be expected because TPS22933's cap is connected to BQ24040, charging the battery, and the battery finally feeding VBAT? I hope not, because (from BQ24040's perspective) VIN < VBAT so it should be in standby, correct?

  • 0
    TI__Genius 10855 points

    Hey Chris, 

    Welcome back! I can answer some of your questions regarding the TPS22933, and I'll loop in a member from our logic team to comment on the SN74AUP1G80.

    The TPS22933 has B2B FETs between VOUT and the 3 inputs, so the output will be protected in this event.

    I'm not sure if I understand the second bonus question, the CAP pin allows an external capacitor to be connected to the input of the internal LDO, which helps stabilize the input voltage for the LDO. Can the cap be connected to GND instead?

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 590 points

    Hi Arthur,

    thanks for the quick reply!

    Well, maybe I misunderstood what we talked about here:

    I thought CAP could be used as a third output (bypassing the LDO), but as I take another look at the datasheet 9.1.2 it seems that it is only working if not using the LDO. Oooops.