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vedder.se forums • Low Voltage on 3.3V and 5V Pin
Page 1 of 1

Low Voltage on 3.3V and 5V Pin

Posted: 28 Mar 2018, 21:35
by vik123
Hello,
I recently soldered my own VESC 4.12. I was able to flash the bootloader on the microcontroller, but when I try to power the vesc or connect it via USB there is no sign of life (no usb, no blue led). The lab power supply is set to 12V and max. current of 0.3 A.

When I measure the pins of 3.3V and 5V on the vesc it shows me actually only around 1.3V (on 3.3V-Pin) and 1.8 V (on 5V-Pin). And around 1 mA from the supply.

I have no idea what is the reason. Perhaps some of you guys?

Best,
Viktor

Re: Low Voltage on 3.3V and 5V Pin

Posted: 30 Mar 2018, 15:08
by arvidb
If the board only draws 1 mA the problem cannot be a short of the supply. It's part of the DRV chip that converts the battery voltage to 5 V, so probably you have a problem with that part of the circuit. Check the DRV page in the schematic and inspect your board around that part - i.e. DRV pins 1-4 and 50-57. Check for shorts, wrong component values, etc. Are you sure the bottom GND + thermal relief pad of the DRV got soldered correctly?

Re: Low Voltage on 3.3V and 5V Pin

Posted: 04 Apr 2018, 20:42
by rew
If DRV gnd is unsoldered, the 5V will be higher than normal.

Re: Low Voltage on 3.3V and 5V Pin

Posted: 09 May 2018, 20:09
by Duo420
You must solder the pad underneath. It's written in the datasheet of the drv8302

Re: Low Voltage on 3.3V and 5V Pin

Posted: 24 May 2018, 18:49
by RyuX
I have exactly the same problem, how could you fix it ?

I am pretty certain my GND Pad on the bottom is soldered correctly as I used solder paste and a reflow station and pressed the IC firmly to the board until even some solder came out on the side. I also don't have any shorts and everything seems fine.. except I also measure 1.8V on the 5V Line..
please help guys

EDIT: Little side note - I don't have the D5 Diode installed as one blew up and I don't have a spare - is D5 needed for operation ?

Re: Low Voltage on 3.3V and 5V Pin

Posted: 25 May 2018, 11:45
by RyuX
I changed the DRV8302 3x already to different new parts.. made sure the bottom GND is soldered.. I also replaced the STM32F405 and flashed it again with STLink.
But I still only measure 1.8V on the 5V Rail from the DRV Chip.

Anyone please have a hint ?

EDIT 2: I tested the PCB with a 18V Lab Supply.. it will draw around 0.9A and when I use the 18V Supply the 5V Rail will show 7.5V - however when using the 44V LiPo it will show only 1.8V.
It's very strange.. The V_SENSE resistors and all the pins connections seem correct :(
What could be the problem ?

Re: Low Voltage on 3.3V and 5V Pin

Posted: 26 May 2018, 23:07
by arvidb
How did D5 blow up?

If the board draws 0.9 A at 18 V (>16 W!) then something should get quite hot quite fast!

The absolute maximum input voltage for the 3.3 V regulator (TC2117) is 6.5 V, so if you've subjected it to 7.5 V it might have died.

Where did you buy your DRV chips?

Re: Low Voltage on 3.3V and 5V Pin

Posted: 29 May 2018, 17:23
by RyuX
I bought my DRV Chips from Mouser and Arrow.
Currently I replaced the D5 Diode and with the 18V Lab Supply I now read 3.25V at 3.3V Rail and 6.82V at the 5V Rail.
The Board was drawing 0.09A before (sorry not 0.9A) and now it is drawing around 0.07A.

Any hints what else I could check ? It's really getting strange

Re: Low Voltage on 3.3V and 5V Pin

Posted: 30 May 2018, 07:09
by rew