BQ25570: When VSTOR reaches VBAT_OV, VOUT drops in unregular intervals !

Aurélien Fillau

Part Number: BQ25570

Hello,

I'm facing an issue with my bq25570 and i don't know why. We've made a first board able to recharge supercapacitors (two capacitors of 0.75F, 2.7V in series) with a VBAT_OV configured at 4.16V and a solar panel of 0.5W in input. All is working fine with this board.

But we have made a second board with a VBAT_OV configured at 5.04V and two supercapacitors of 35F, 2.7V and the same solar pannel in input. But when VBAT reaches 5.04V (even before but i'm not sure), sometime VOUT falls down that makes my MCU to be reset (as soon as i unplug the solar panel, it stabilizided again a little bit).

if you have any ideas or suggestions please feel free to reply. I'm not an electronician, i'll try to do my best to answer. Here is the shematic :

Schematic_laborde_01.pdf

Thank you in advance.

Best regards,

Aurélien

over 8 years ago

0 Raheem over 8 years ago

TI__Mastermind 21590 points

Hello,
Looking at your schematic, I noticed that the sum of your resistors that has the midpoint connected to VOUT_SET (ROUT1 and ROUT2) for 5V output is below the minimum required which is 11 mega ohms. Please adjust these and see if that fixes this issue.
Regards,
Raheem

0 Aurélien Fillau over 8 years ago in reply to Raheem

Expert 1710 points

Hello,

Thank you very much for your reply. The ouput is configured to be at 3.3V so ROUT1=4.22MΩ and ROUT2=7.5MΩ. This configuration fits the minimum required 11MΩ and is no greater than the 13MΩ advised by the documentation.

Regards,

Aurélien

0 Raheem over 8 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

Hi,
What is the load on the output?
Regards,
Raheem

0 Aurélien Fillau over 8 years ago in reply to Raheem

Expert 1710 points

Hi,
I have connected to vout a stm32l0 + several i2c slaves and a sigfox module. At startup it can consume up to 20mA. When vbat is under 5v, all is working fine. I found this post :

They have a similar problem but they don't seem to have found solution :'(
Regards,
Aurélien

0 Raheem over 8 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

Hi,
Can you please post scope shots showing VBAT. VIN, VSTOR and VOUT when this issue occurs?
Regards,
Raheem

0 Aurélien Fillau over 8 years ago in reply to Raheem

Expert 1710 points

Hi,

Actually, the issue also occurs when VBat is configured at 4.8V (under 5V). I will post scope shots as soon as possible.

Thank you,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Aurélien Fillau

Expert 1710 points

Hello,

Here is a screenshot when the issue occurs :

We can clearly see that Vout decreases under 1V that makes my MCU to reset. Other indications : on Vin, just before the issue occurs, i can see many glitches, i suppose at this moment, the bq25570 enters a different state.

If you have any ideas how to solve this issue, it would be great :)

Best regards,

Aurélien

0 Raheem over 7 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

Hi,
Looking at the schematic, I noticed a couple of issues. You have VBAT_OK_HYST = 1.76. This is lower than the minimum which is 1.95V. VBAT_OK_PROG is also below VBAT_UV(1.95V) which is the minimum.
Regards,
Raheem

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

Hi,

Thank you for the reply. Do you think it could explain the issue ? For now, i found a workaround. It consists in adding a 10uF capacitor on VBAT pin as close as possible to the BQ. With this patch, my board has run for 10 days without rebooting. I will change VBAT_OK_PROG and VBAT_OK_HYST also and test with this modification.
I'm not sure at 100% my capacitor will solve the problem, i need to do more tests.
If you have any other ideas, don't hesitate.

Best regards,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Aurélien Fillau

Expert 1710 points

Hello,

I have tested with the right values for VBAT_OK_PROG and VBAT_OK_HYST. I have configured as following :

ROK1 = 5.1MOhm
ROK2 = 4.7MOhm
ROK1 = 3.3MOhm

-> VBAT_OK_PROG = 2.32V
-> VBAT_OK_HYST = 3.10V

But even with this configuration, VOUT is still drooping after a while and as a consequence my board continues rebooting ...

0 Aurélien Fillau over 7 years ago in reply to Aurélien Fillau

Expert 1710 points

Hello,

For your information, i have 5 boards, all the boards have the same behavior, so i don't think it is a matter of soldering.

Regards,

Aurélien

0 Raheem over 7 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

Hello,
Can you also post screen shots of VSTOR and VRDIV when this occurs. I'm currently trying to replicate this. I'll let you know what i find.
Regards,
Raheem

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

Hello,

Thank you very much for the time you are taking about this issue. I ll will try to send you screen shots as soon as possible.

Best regards,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

Hello,
Did you succeed to replicate the issue ? I'm also trying to to replicate it on my side, but i didn''t succeed to catch VRDIV with my oscilloscope for now.
Regards,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Aurélien Fillau

Expert 1710 points

Hello,

Here is a screenshot of VRDIV (blue) and VOUT (yellow) :

I have only two channels with this oscilloscope, so i wasn't able to catch more entries. As you can see, VOUT falls under 2V sometimes. When i put my hand in front my solar pannel, VOUT stop drooping and stays stable at 3.3V.

Hope this shots will help you to find out what is the issue :)

Regards,

Aurelien

0 Aurélien Fillau over 7 years ago in reply to Aurélien Fillau

Expert 1710 points

Hello,

Any update ? Did you succeed to reproduce the issue ?

Regards,

Aurélien

0 Raheem over 7 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

Hello,
This seems to be an instability issue. Try adding a 100uF capacitor on the BAT pin which should help stabilize the system and prevent the voltage drop.
Regards,
Raheem

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

Hello,

I have even put a 10uF capacitor on VBAT and yes it seems to have stabalized the system, but i'm not sure at 100% it won't happen again :s
If you have any other ideas, don't hesitate to share ;)

Regards,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

Hello,

Firstly, happy new year :)

But bad news, I'm still having troubles with my bq25570, it continues reseting sometimes when it is in charging mode ... even with 100uF capacitor added on VBAT :s
Do you think i can add a capacitor with a bigger value ?

Best regards,

Aurélien

0 Aurélien Fillau over 7 years ago in reply to Raheem

Expert 1710 points

It is very weird, because it is only when my device is in charging mode (that is to say when i have a voltage on VIN). It starts reseting when i want to send a radio frame that consumes between 38mA and 50mA !

0 Raheem over 7 years ago in reply to Aurélien Fillau

TI__Mastermind 21590 points

This issue was resolved here: e2e.ti.com/.../653835

Regards,
Raheem

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BQ25570: When VSTOR reaches VBAT_OV, VOUT drops in unregular intervals !