ESP32D2WD available pins

[onehorse]

I am looking at the data sheet of the ESP32 D2WD 5 mm x 5 mm package with internal 16 Mbit flash and it says:

"ESP32-D2WD has a 16-Mbit, 40-MHz embedded flash, connected via pins GPIO16, GPIO17, SD_CMD, SD_CLK,
SD_DATA_0 and SD_DATA_1."

1) I assume we cannot connect anything to GPIO16, GPIO17, SD_CMD, SD_CLK,
SD_DATA_0 and SD_DATA_1 since these are being used by the internal flash. Or is it the case I should expose these pins to the user in case an additional external flash could be added?

2) If I cannot use GPIO16 and 17 in the design, can I use instead SD_DATA_2 and SD_DATA_3 as GPIOs 9 and 10 just like with the ESP8285?

3) Also MTDI needs to be pulled up to allow the internal 1.8 V internal LDO for the internal flash. Are there any other changes necessary to the strapping pins?

Thanks for the help!

[onehorse]

Can no one from Espressif offer some answers here? Should I ask somewhere else? Suggestions?

Thanks for you help!

[WiFive]

The problem is all the vdd_sdio domain pins will be 1.8v so you can break them out if you want, mostly a design decision.

[onehorse]

Thank you for your reply!

I've been trolling through the past posts on the D2WD device looking for answers. I probably do not want to expose 1.8 V pins on a 3V3 boards.

One more thing if I may, the VDD_SDIO probably shouldn't be connected to 3V3. Do I need a bypass cap on this pin to GND then or should I just leave it unconnected?

[WiFive]

Yes not sure whether any capacitance is recommended on vdd_sdio and there's also this

When VDD_SDIO 1.8V is used as the power supply for external flash/PSRAM, a 2-kohm grounding resistor should
be added on VDD_SDIO.

[onehorse]

Does this mean a 2 kOhm external pull down resistor on VDD_SDIO? This seems rather strange...

I am using the internal flash of the D2WD so I am not sure this would apply? Where did you find this note? And is there a hardware reference guide specifically for the D2DW IC? That would be helpful...

[WiFive]

Yes I think it is to make sure 1.8v goes to zero quickly when the chip powers down to compensate for the external bulk capacitance. Either that or the internal regulator requires a minimum load to maintain a stable voltage. I am not sure why it wouldn't apply to d2wd then also and could be related to some of the voltage boost and drive strength changes.

It is from the esp32 datasheet and not to my knowledge.

[onehorse]

I appreciate the info, thanks for your help.

I more or less completed the design but there is little advantage to using the D2DW other than the enbedded flash and some downsides, two fewer GPIOs and more difficult to solder. I'll give it a try ayway and see if I can get the board to work.

Here is what the board looks like:

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ESP32_D2DW.jpg (115.52 KiB) Viewed 12132 times

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It is basically the same as the ESP32 Development Board I designed a year ago and for sale at Tindie.