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1. Introduction
The ST67W611M1 features a shutdown mode with a typical current consumption of 200 nA. This mode is entered by forcing the CHIP_EN module low which maintains the module in reset.
2. CHIP_EN hardware implementation
CHIP_EN is a 3.3 V signal that needs to be provided by the Host which controls the ST67W611M1. A direct connection from the CHIP_EN module pin (number 17) to a host pin is therefore mandatory. A 100 nF capacitor must be added between CHIP_EN and the ground.
A delay of at least 3.3 ms must be guaranteed between the module power-up and CHIP_EN going high.
CHIP_EN is one of the two bootstrap pins that control the boot mode of the ST67W611M1. See the BOOT related page for more details.
1.2 V VDDIO use case
When VDDIO is configured to 1.8 V, all host interface signals are expected to operate at the same 1.8 V logic level. However, the CHIP_EN input of the ST67W611M1 still requires a 3.3 V high level to ensure proper module activation.
If the host GPIOs only support 1.8 V output levels, a 1.8 V ↔ 3.3 V level shifter must be inserted on the CHIP_EN control line. This guarantees that the ST67W611M1 receives the required 3.3 V logic‑high level while maintaining safe voltage levels on the host side.
As an alternative, the host can drive CHIP_EN in open-drain mode1, with an external 33 kΩ pull-up resistor to VDD33. This approach eliminates the need for a dedicated level shifter, provided that the host I/O driving the CHIP_EN signal is 3.3 V tolerant. This configuration increases the overall shutdown current consumption of the ST67W611M1 subsystem by 100 µA.
1 This configuration can be set by modifying the .ioc STM32CubeMX file or by editing the project's main.c file and replacing the I/O driving CHIP_EN configuration line:
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP
with
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD
3. CHIP_EN state control
The host controls the ST67W611M1's CHIP_EN by forcing it low or high. In the short time until the host boots and takes control of CHIP_EN, this pin will be floating and the ST67W611M1 will be in an unknown state (see figure below).
It has been confirmed that this short time during which CHIP_EN is floating doesn't affect the module functionality. It can still be avoided by making sure CHIP_EN is forced low from board startup through an onboard pull-down. Another option is to connect CHIP_EN to a Host pin that has a known default level before the host firmware starts running.
3.1. STM32U5 example
As an example in the case of the STM32U5, JTAG and SWD pins have known default levels thanks to internal 40 kΩ pull-up or pull-down. These pins are listed below. More details are detailed in the STM32U5 reference manual.
- PA15: JTDI in pull-up
- PA14: JTCK/SWCLK in pull-down
- PA13: JTMS/SWDIO in pull-up
- PB4: NJTRST in pull-up
This kind of changes has been tested. The figure below shows the case with CHIP_EN connected on the STM32U5 PA14 pin which features a pull-down. As can be seen, CHIP_EN is no longer floating and is kept low until the firmware forces it high.
It must be noted that:
- Using a JTAG pin to control CHIP_EN means that JTAG is no longer available for the STM32U5 programming/debug.
- Using a SWD pin to control CHIP_EN means that SWD and JTAG are no longer available for the STM32U5 programming/debug. Debug would then be fully disabled, and subsequent programming would have to be done via bootloader.
4. X-CUBE-ST67W61 software system behavior
Starting X-CUBE-ST67W61 1.0.0 release, shutdown feature is supported. The module is shut down after calling CLI command "quit". See the software related documentation for more details.