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DoMl
Visitor II
March 27, 2024
Solved

L6924D random status pin flicker in shutdown

  • March 27, 2024
  • 1 reply
  • 1014 views

Hello,

i have a board with 10 L6924D on it, the schematic of each channel is derived from STEVAL-ISA076V1(*). Charging works as planned, CC/CV, correct max voltage and charge current and charge-end-current. Both status pins are connected to LEDs as on the devboard, signaling correctly for charging, completed or error. All channels are sharing the 5V input and one line connecting all shutdown pins. The shutdown-line is pulled down by a N-fet to activate the charging or is pulled high to 5V with 10k.

When activating the shutdown, the voltage on all chips is a clear 0V or 5V transition and all 10 channels stop charging as expected.

What is not as expected, are the flickering status LEDs. Sometimes all are on, sometimes just one of them, sometimes none, and that random for each of the channels. One or two out of ten randomly fade between the LEDs within seconds and I can measure all voltages between 0V and 5V by multimeter and oscilloscope. There is no difference between battery connected or not.

It seams, that the status pins have no clear control signal for on or off when the IC is in shutdown.

Is there a way out?

Regards, Dominic

 

 

*https://www.st.com/resource/en/data_brief/steval-isa076v1.pdf

This topic has been closed for replies.
Best answer by Peter BENSCH

Welcome @DoMl, to the community!

If I understand you correctly, you expect the open drain outputs ST1 and ST2 to work correctly even in shutdown?

However, this is not possible as the internal logic and VREF are switched off in shutdown to save power. If necessary, you should also switch off the LED completely during shutdown, e.g. via a p-ch FET that is controlled directly by pin SD?

Incidentally, the irritating flickering is probably due to the fact that small currents flow via the internal parasitic pn junctions despite the shutdown, which are in the reverse direction when switched on and then have no effect. As soon as you switch off the LED with the proposed p-channel FET, these currents should no longer occur.

Hope that helps?

Regards
/Peter

1 reply

Peter BENSCH
Peter BENSCHBest answer
Technical Moderator
March 27, 2024

Welcome @DoMl, to the community!

If I understand you correctly, you expect the open drain outputs ST1 and ST2 to work correctly even in shutdown?

However, this is not possible as the internal logic and VREF are switched off in shutdown to save power. If necessary, you should also switch off the LED completely during shutdown, e.g. via a p-ch FET that is controlled directly by pin SD?

Incidentally, the irritating flickering is probably due to the fact that small currents flow via the internal parasitic pn junctions despite the shutdown, which are in the reverse direction when switched on and then have no effect. As soon as you switch off the LED with the proposed p-channel FET, these currents should no longer occur.

Hope that helps?

Regards
/Peter

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