Operating the ESP32-WROOM32-UE at low supply voltage (2,7V - 3.0V)

[Chris_Darwin]

Hello,

we have a topic here, and would be glad if one of the espressif application ingeneers could help answering these questions.

We need to operate the ESP32-WROOM32-UE (changing to another type is not possible) at low operating voltage in the range from 3,0V down to 2,7V.

Concering this issue, we have found several information in technical documents:

a) the data sheet (esp32-wroom-32e_esp32-wroom-32ue_datasheet_en.pdf) states, that the Power supply voltage is at minimum 3.0 V.
b) for another type of the family (see esp32-wroom-32_datasheet_en.pdf) the minimum power supply voltage has been changed from 2,7 upwards to 3,0V in the Revision History
c) It seems to us, that the SPI flash is the main reason, why the minimum operating voltage of ESP32-WROOM32-UE is 3,0V and not lower (see esp32-wroom-32e_esp32-wroom-32ue_datasheet_en.pdf on page 13 ("The module integrates a 3.3 V SPI flash, so the pin MTDI cannot be set to 1 when the module is powered up.")

The questions we have here are the following:

d) what might/will happen, if the operating voltage of ESP32-WROOM32-UE drops down to 2,9V, 2,8V, 2,7V? Which components of the part might stop working correctly: SPI flash, WiFi, Bluetooth, or other?

e) is there possibly a set of parts of ESP32-WROOM32-UE (identified by product number etc.) which is able to run at e.q. 2,7V, and which uses a SPI flash with e.g. 1,8V? (see point b: has the operating voltage for ESP32-WROOM32 set up to 3,0V perhaps due to change from a 1,8V SPI flash to a 3,3V Spi flash?)

Thank you very much in advance, a qualified answer to these question will help us a lot.

Have a nice day
Chris

[WiFive]

Most flash chips are specced 2.7v-3.3v, I think the RF analog section is what requires 3v.

[becorey]

Use a DC Boost converter to provide the proper voltage. Do you have size / cost / thermal constraints that prevent doing that?

[Chris_Darwin]

In our application we have - beside a 220V power supply regulated down to 5 V - an accumulator emergency operation, which will use 3 x NiMH accu cells. That gives us a voltage of 3 x 1,2 V = 3,6V to operate. To switch between power supply and accu we will use a LTC4412, which is kind of an "ideal diode" with no voltage drop, but even a 3V3/3V0 LDO will take us away at least 0,2V.

So there remains for us only a low operation voltage range at all, and the accus will also go down to 3,3V/3,0V when discharging.

That is the reason why we are interested how it is possible to drive the ESP32-WROOM32-UE at low supply voltage range (2,7V - 3.0V).

Any step up converter is not forseen in our application design up to now (size/cost constraints).