MP2690 - VNTC did not turned off at Sleep mode

Battery Management
1

We are using MP2690 in a handheld battery device. We noticed following symptom:

  1. Put the part in to Boost mode;
  2. Insert 5V into VIN, part is switched to pass-through mode;
  3. Remove supply to VIN & load at output;
  4. Part should go into Sleep mode & VNTC should turned off, but VNTC remained ON.

As we are using the load detection circuit described in MP2690 specification, VNTC not turning off will cause the circuit to be unfuctionable. We try replacing VNTC source in the load detection circuit to SYS, it didn’t work as well.
We would like to ask MPS if there is a workaround on this matter, as we didn’t include a button in design.

2

Did you measure Vin under the fault condition? Vin has to be less than 2V to invoke sleep mode. Perhaps there is some leakage path holding Vin high?

3

The other way it enters sleep mode from Boost mode is that the output is unloaded for a certain time. Are you sure your application is drawing low enough power for long enough to trip the “unloaded” detection?

4

We measured Vin under fault condition, it is 0V.

5

The load will be completely disconnected from SYS when not used. There’s no addtitional load on SYS port besides some ceramic capacitors & the load detection circuit. Also, SYS output voltage based on oscilloscope is at 160mV max. during fault condition.

6

We monitored the fault condition for 15mins, Vntc remained high.

7

One thing to note, this fault is about transition to Sleep mode from Pass-Through mode, not Boost mode. Please refer to below flow chart:
Boost Mode -> Pass-Through Mode -> Disconnect both VIN supply & load at SYS (disconnection order has no effect) -> Vntc remained High & SYS is at 0V.

The IC is remained at pass-through mode after the fault. The evidence is that voltage level at SYS is following VIN voltage.

8

Hi sxaw,

Welcome to the MPS Technical Forum! I will begin looking through the details of your application you’ve provided so far and give an update soon.

9

Looks like you got the experts interested. I suspect you are in “torch” mode somehow, which seems to shutdown the lightload detection and prevents sleep mode.

10

Thanks Bryan. Really appreciate your help.

11

We also have the same doubt but can’t really verify it as the pad is removed due to not used. We also monitored waveform at PB but didn’t see it go low.

12

Hi sxaw,

I think we found your issue with the MP2690. I can’t say everything on the forum about this issue, but we can help give you more information if you email us at mpsnow@monolithicpower.com. I’ll send you some slides about this issue and how it can be fixed. It involves external circuitry regarding the power button.

Thanks,
Brendan Schoemehl
Field Applications Engineer
Monolithic Power Systems | MPS Now

13

Hi Brendan,

Thank you very much on your support.
I have emailed to [mpsnow@monolithicpower.com] with my company email. Please check & let me know at the forum if it failed to reach you.

14

Has someone reached out to you yet? I haven’t personally seen an email from you, so I want to make sure you’ve been taken care of. If not, please let me know your company email so that I can get in touch with you.

Thanks,
Brendan

15

Hi Brendan,

Thanks for reaching out. I dropped my email to mpsnow@monolithicpower.com on this Tuesday but so far didn’t have a reply. Can you email me at sxaw@vs-i.com? And also notify me here at the forum once you did? I just want to make sure if it wasn’t blocked by my company firewall.

16

I found your first response. I sent a reply back to you, I hope you received it.

Brendan

17

Hi Brendan,

Yes, I have received it. Thank you very much.
It’s a brilliant solution. Cheaper than what we plan to implement & will not restrict user to charge & use the device. We will implement & test it.

18

Sure thing. Keep me posted, just email me if you have any questions.

Thanks,
Brendan

19

The workaround or solution should really be published here, so that others may know what issues this part has and how to solve it before designing into their own product.

Evan

20

For the workaround, my original idea is to use several MOSFETs to block USB supply to VIN when the IC is in Boost mode. So the fault would not occurred but the drawback is user cannot charge battery or divert the load from battery to external supply.
What Brendan proposed to us is to automatically turn on Boost Mode when user remove the external supply to VIN. If there is a load connected, user will only experience momentarily disruption; if there’s no load, Boost will turn off automatically after 16s. It uses a NPN BJT with several resistors to create the feedback from VIN to PB. I’m not allowed to post details here as the slides are marked as confidential.