I recommend to use the S6AE102A for your application. The S6AE102A supports a hybrid capacitor charging function. Refer to following block diagram and wave form.
If you use S6AE101A or simple diode protection, it will taking longer start-up time.
If you use S6AE102A with hybrid capacitor charging, it will be Quick start-up time using both VSTORE1 (Small Capacitance) and VSTORE2 (Large Capacitance).
Thanks for the response Eiji.
It is a space constrained wearable system so the larger 102A die size wont fit. It seems however that the 101A and simple diode protection method are basically equivalent for battery less system so we will go with the simple method. To be honest i am still not certain what are the advantages of the S6AE101A. As i have said it seems like it only operates in a small margin of voltages while a simple OVP diode with buck-boost converter would utilize the full capacity of the supercap.
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Refer to following block diagram and waveform.
I will show the benefit and consideration each circuits.
- Use full capacity when the light is dark
- Take long charging time when the supercap was empty
- VOUT voltage will be toggled due to current of MCU Power-On-Reset
- Total BOM cost will be high due to extra circuit
- Very low quiescent current (250 nA),
- Low BOM cost, Simple Circuit
- Including control circuit (power gating, cutoff voltage ...)
- It can't use full capacity when the light is dark
- Take long charging time for 1st start-up
Thanks Eiji, thats much more clear on the differences. So what you are saying is the S6AE101A avoids the power toggling problem by allowing the supercap to charge to VOUTH after which it has (VOUTH-VOUTL) voltage margin to safely perform the boot operation. With the simple setup, if the supercap is close to the low voltage dropout of the boost converter then it may be at risk of switching on and off if the PSoC draws too much current at boot.
Our implementation avoids the toggling problem in firmware by reading the supercap voltage via ADC and putting the PSoC into deep sleep well before reaching the boost dropout voltage (say like 0.4V). I think this will allow us meet our requirement for night operation while also avoiding complicated power up circuitry as you pointed out.
Much thanks for the clear explanation,