Flash And Psram; In-Package Flash And Psram - Espressif Systems ESP32 Hardware Design Manuallines

Chapter 3. Schematic Checklist
Attention:
• CHIP_PU must not be left floating.
• To ensure the correct power-up and reset timing, it is advised to add an RC delay circuit at the CHIP_PU
pin. The recommended setting for the RC delay circuit is usually R = 10 kΩ and C = 1 μF. However, specific
parameters should be adjusted based on the characteristics of the actual power supply and the power-up
and reset timing of the chip.
• If the user application has one of the following scenarios:
– Slow power rise or fall, such as during battery charging.
– Frequent power on/off operations.
– Unstable power supply, such as in photovoltaic power generation.
Then, the RC circuit itself may not meet the timing requirements, resulting in the chip being
unable to boot correctly. In this case, additional designs need to be added, such as:
– Adding an external reset chip or a watchdog chip, typically with a threshold of around 3.0
V.
– Implementing reset functionality through a button or the main controller.

3.3 Flash and PSRAM

ESP32 requires in-package or off-package flash to store application firmware and data. In-package PSRAM or off-
package RAM is optional.

3.3.1 In-Package Flash and PSRAM

The tables list the pin-to-pin mapping between the chip and in-package flash/PSRAM. Please note that the following
chip pins can connect at most one flash and one PSRAM. That is to say, when there is only flash in the package, the
pin occupied by flash can only connect PSRAM and cannot be used for other functions; when there is only PSRAM,
the pin occupied by PSRAM can only connect flash; when there are both flash and PSRAM, the pin occupied cannot
connect any more flash or PSRAM.
Table 2: Pin-to-Pin Mapping Between Chip and In-Package Flash
ESP32-U4WDH
SD_DATA_1
GPIO17
SD_DATA_0
SD_CMD
SD_CLK
GPIO16
GND
VDD_SDIO
Table 3: Pin-to-Pin Mapping Between Chip and In-Package PSRAM
ESP32-D0WDR2-V3
SD_DATA_1
SD_DATA_0
SD_DATA_3
SD_DATA_2
SD_CLK
GPIO16
GND
VDD_SDIO
Espressif Systems
In-Package Flash (4 MB)
IO0/DI
IO1/DO
IO2/WP#
IO3/HOLD#
CLK
CS#
VSS
VDD
In-Package PSRAM (2 MB)
SIO0/SI
SIO1/SO
SIO2
SIO3
SCLK
CE#
VSS
VDD
12
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