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STM32L476 high current draw before programming

Question asked by Willette.Gary on Jan 6, 2017
Latest reply on Jan 30, 2017 by Trinh.Danh

Our application uses the SMT32L4 in a 4-20mA loop-powered transmitter. VCC on this device is 3V. The typical current draw once the product is operational is approximately 8mA @ 3v. We are utilizing the bootloader to program the mcu with UART1 on pins 68-69 (PA9 and PA10). On some boards, prior to programming, there is approximately 40-50mA current draw on the 3V supply. Our supply is rated for 50mA and once we attempt to initiate bootloading, the current consumption increases beyond that limit. If we provide enough current by increasing the supply, the device programs successfully. Once programmed, the total draw on the 3V supply is the expected 8mA.

I am wondering if there is a known operation/current consumption for these devices before they are initially programmed. Also, I see that the bootloader can use USART1/2/3, I2C1/2/3, and DFU (USB). Which ports/pins are utilized for the USART and I2C channels during bootloader operation? There are several ports that can be configured for each of these channels during normal operation, so it is difficult to determine the exact pin configuration of the device when it is in bootloader mode.

Thank you!