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bvn123
bvn123
Associate II
February 26, 2019
Question

Steval-FKI433V2 doesn't work with external power supply for Nucleo and S2-LP, when the power for ST-Link doesn't supplied.

  • February 26, 2019
  • 1 reply
  • 518 views

Hello.

I want to decrease power consumption of Steval-FKI433V2 and to cut ST-Link PCB part, but later.

Conditions:

  1. The modified program SDK_Chat.c (from S2-LP DK example) is loaded to the Nucleo uC. Uder this program Nucleo+S2-LP send back received data. The Steval is not connected to COM-port and works autonomously.
  2. 3V7 battery is connected to CN7/pin6 (E5V) (3V7 is enough for 3V3 LDOs on Nucleo and ST-Link).

If JP5/pins2,3 are shorted: Nucleo, S2-LP and ST-Link are powered, the Steval works properly (it sends back received data) but the consumption is changed between 52mA and 65mA and two-colored LED is blinking approx. once per second.

If JP5 pins are not shorted and 3V7 battery is connected to CN7/pin18(+5V), only Nucleo and S2-LP are powered (ST-LINK is not powered). The consumption is 20mA, but device doesn't work.

As ST-Link's uC is not powered, too small voltage is present in the NRST net, I pulled it up to 2V85, but device doesn't work.

I see also, that when powered, ST-Link provides 8MHz to Nucleo's uC (MCO net), but in SDK_Chat.c HSI oscillator is selected, so external 8MHz should not be used.

Question: what else should I do to power only Nucleo and S2-LP now, when ST-Link is not cutted and should not be supplied with power? May be some special changes in SDK_Chat.c program must be done?

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    1 reply

    bvn123
    bvn123Author
    Associate II
    February 27, 2019

    I've solved the problem.

    In SDK_Chat.c remove the string '#define USE_VCOM' (place delimiter '//' before it):

    //#define USE_VCOM

    3V7 battery:

    '+' is connected to CN7/pin18 or CN6/pin5 (+5V); '-' to CN7/pin20 or CN6/pin6 (GROUND);

    JP5 (3 pins): jumper is removed;

    R=1k: between CN6/2(+3V3) and CN6/3(NRST) (If ST-Link part of PCB would be cut, R may be increased up to 4k7...10k);

    3V7 consumption: 18mA, when green LED is off, 20mA - LED on.

    To decrease the consumption,

    remove the strings 'SdkEvalLedToggle(LED1);' in SDK_Chat.c (green LED off, consumption 18mA):

    remove R32 (red LED off, consumption 16mA).

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