STM32L011D3 and L6387ED problem

[Piotr1]

Posted on March 24, 2018 at 12:39

Hi,

I'm using STM32L011D3 to control L6397ED driver. Everything works fine until supply voltage on L6387ED drops below threshold voltage (typ. 6V). When voltage drop on driver occurs, supply voltage on microcontroller is stable and equal to 3.3V (tested with an oscilloscope).  Is it possible that when supply voltage on driver drops, it draws relatively hight urrent from microcontrolers GPIOs, what causes microcontroller reset?

[T J]

Posted on March 24, 2018 at 21:25

Are you running a long lead ?

the inductive kickback is not insignificant.

you may need to separate the power with diodes and add capacitance to the processor power line.

[Piotr1]

Posted on March 24, 2018 at 21:36

Thank you for answer.

What do you mean 'long lead'?

Inductive kickback is supressed by Schottky diode. Power line of microcontrolled is very well filtered, as you mentioned with diodes and capacitors. Nothing else is connected to supply line.

GPIOs are connected directly to driver. I wonder if adding serial resistor between microcontroller and driver will help.

[T J]

Posted on March 25, 2018 at 14:31

you may need a resistor in series Yes.

I cant find your chip,  L6397ED

do you have a link ?

[Piotr1]

Posted on March 25, 2018 at 15:27

Here is link:

http://www.st.com/content/ccc/resource/technical/document/datasheet/09/06/7a/6f/1d/a6/45/f5/CD00173127.pdf/files/CD00173127.pdf/jcr:content/translations/en.CD00173127.pdf

 

[T J]

Posted on March 25, 2018 at 16:00

So your fault is, when you power down the LED driver, your processor resets ?

it is possible that you can draw excessive current from a GPIO set to output, the easy fix is a 1K in series. 3mA max

the Logic input of the L6387E will be ok with a 1K

great chip to see.. cheep too.

on page 6/17 DC operation,

VCC 3

Supply voltage 17 VSymbol Pin Parameter Test condition Min. Typ. Max. Unit

VCCth1 VCC UV turn-on threshold 5.5 6 6.5 V

VCCth2 VCC UV turn-off threshold 5 5.5 6 V

I guess you shouldn't trigger the UV turnOff threshold,

I guess it's suggesting the external Fets may be switched on when VS drops below the UVturnOff threshold

there must be an app note.

how did you connect your load to this chip ?

[Piotr1]

Posted on March 25, 2018 at 19:50

Yes, low MOSFET is switched on when supply current of a driver drops below UVturnOff threshold.

It's halfbridge protected by Schottky diodes. Between drivers outputs and MOSFETs gates are serial resistors.

Thank you really much for your help, I will add serial resistors between driver and uC and check what will happen.