Impedance Control for U4 Design

brooks

brooks

Regarding U4, which pins would you reasonably guess should be impedance controlled? And of those which should be pair routed, which pins pair with which pins? and which would be single ended? this is for a mockup so you don't have to be 100% right.

flux

For U4, you’ll generally want controlled-impedance routing on any high-speed digital I/O. In this design that’s primarily the SPI and SD-card interfaces. There are no true differential pairs broken out from U4 (USB D+/D– and CANH/CANL sit on external transceivers), so all of these will be single-ended 50 Ω lines.

Table

Signal NameU4 Pin (I/O)Impedance ControlPair Routed?Pair With
VSPI_CLKIO1850 Ω single-endedNoN/A
VSPI_MISOIO1950 Ω single-endedNoN/A
VSPI_MOSIIO2350 Ω single-endedNoN/A
HSPI_CLKIO1450 Ω single-endedNoN/A
HSPI_MISOIO1250 Ω single-endedNoN/A
HSPI_MOSIIO1350 Ω single-endedNoN/A
SDIO_CLKIO18 (shared)¹50 Ω single-endedNoN/A
SDIO_CMDIO1550 Ω single-endedNoN/A
SDIO_D0IO250 Ω single-endedNoN/A
SDIO_D1IO450 Ω single-endedNoN/A
SDIO_D2IO12 (alt²)50 Ω single-endedNoN/A
SDIO_D3IO550 Ω single-endedNoN/A
CANBUS_TXIO1650 Ω single-endedNoN/A
CANBUS_RXIO1750 Ω single-endedNoN/A
  1. On many ESP32 modules the VSPI_CLK pin doubles as SDIO_CLK; if you’re only using one interface at a time you can share the trace impedance spec.
  2. SDIO_D2 may be remapped on certain GPIOs—be sure to confirm your pinmux if you change defaults.
If you later expose USB D+/D– or CANH/CANL directly from the module, those would be routed as 100 Ω differential-impedance pairs. All other GPIOs are low-speed and can use standard 10 mil traces without controlled impedance.
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6
IO33
VSPI_CLK
HSPI_MOSI
IO22
IO32
IO16
IO17
IO36_INPUT
IO26
IO27
HSPI_MISO
IO39_INPUT
IO4
IO35_INPUT
IO5
IO34_INPUT
IO21
VSPI_MOSI
RESET
IO0_BOOT
IO25
HSPI_CLK
VSPI_MISO
U4
Manufacturer Part Number
ESP32-DEVKITC-32D
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