Hello,
I am having odd behavior (or I do not fully understand) the TPS63050 Soft-Start feature. I do not see what the datasheet is stating.
I am using TPS63050 dev kits (WLCSP and QFN) for verification. I have edited the WLCEP board for adjustment of Vout and soft-start while keeping the QFN DeKit the same:
TPS63050EVM-679 (QFN Flavor, unchanged)
TPS65030EVM-180 (WLCSP Flavor, edited for 4V out, 2msec startup).
I have attached a PDF which describes the situation in detail. But to reiterate:
(1) Soft-start is not so soft, it seems to work for only a few hundred microseconds, and then ir goes back to normal start siwtching currents
(2) voltage on soft-start cap should be ~1.3V, and I do not see this, I see it track with Vin. This is the same on both edited and non-edited EVMs.
(3) Soft-Start capacitor calculation is not accurate (likely b/c the voltage is not matching). My calc is inside the document.
(4) I can see softstart voltage continue to rise above 1.3V (even > 2.6V), and settle much after Vout has settled. So even the timing between SS voltage and Vout do not track together.
Please review the document, and let me know if I am misinterpretating the datasheet. There is no soft-start diagrams in this datasheet, and the wording is poor. The document has plots.
END GOAL OF THE CIRCUIT:
- Our battery is very small and has some ESR. I wish to use soft-start and Lim0,1 = low, to reduce switching currents and Vout ramp, to reduce the transient switching lows on the battery. These transients are creating a large enough voltage drop to drop out our system pre-maturely.
VIN: 3.4V, Vout = 4.0V, Iout = 25uA during soft-start, and typical 50mA transient in regulation.
