[STM32L4] [PWR] When MCU Vdd is given 1.8V supply, the LPUART and USB do not work

[sunny]

Posted on August 19, 2016 at 06:08

Hi,

I am using STM32L4 - Vdd @3V (at 48MHz and 80MHz). For both the clock frequencies, i.e. 48MHz and 80MHz, I am able to use the LPUART1 and USB (Device Mode) properly.My RCC configuration is:

LPUART1

- 

LSE Oscillator and LSE Clock.

MSI Clock Range - MSI Range 6 (Voltage Scaling @ Run Range 1) PLL Source - MSI PLLM - 1 PLLN - 24 PLLP - 7 PLLQ - 2 PLLR - 2 SYSCLKSource - PLLCLK AHB CLK Div - 1 (SYSCLK) APB1 and APB2CLKDiv - 1 (HCLK) USBCLKSource - PLL But when the Vdd is changed to 1.8V (SDCard at 3V), the LPUART1 and USB (Device Mode), does not work. The code is executing properly, but I do not see any data being sent out from the LPUART1. Similarly, I do not get the USB Interrupts.I referred the PWR chapter in the Reference Manual (RM0351), but did not find anything which mentions that the LPUART1 and USB will stop working when the Vdd is at 1.8V.One more observation is that, when the Vdd is @1.8V, the LPUART1 works till the SYSCLK is configured at 32MHz. But it does not work when the SYSCLK is configured to 48MHz which is required for the USB to work.Awaiting your reply.Thanks,Sunny #stm32l4 #usb #mcu@1.8v #lpuart1

[sunny]

Posted on August 19, 2016 at 13:28

Hi,

I am able to solve this issue.It was problem from my HW connection to VddUSB.Thanks,Sunny

[Walid FTITI_O]

Posted on August 19, 2016 at 17:14

Hi bhayani.sunny,

Thanks for the sharing your finding , but can you further more explain what kind of HW connection to VddUSB (it was no connection ? bad connection ? boot strap ..?)

To make clear for other forum users if that face similar issue.

-Hannibal-