LM3658: LM3658SD-B/NOPB can't charge SuperCAP upto 4.2V

Just to update,

After IC replaced, we got VBAT = 1.67V in all reworked boards. Please suggest.

Hi,

In pre-qualification mode, does LM3658 able to charge fully discharged battery? (Whether it supports 0V charge feature?)

As it is not mentioned in the datasheet. Awaiting for the support.

Hello Mr. John,

Many thanks for your reply,

Please see my in-line response below,

A couple of things to check:
1.) When VBAT = 1.67V, what voltage do you see at ISET? ----> Viset = 0.238V
2.) Also what is voltage at input? ----> Vin = 5.287V

A couple of things to double check:
1.) Problem devices are LM3658SD-B with marking L156B. ----> Yes. L156B marking is there.
2.) USB_sel is configured high. ----> USB_sel is pull down with 10k.

Que: We have produced 200 boards, and all has LM3658SD-B with marking L156B. Can you please share batch code or other information to track whether we have used damaged charger IC?

Looking forward to your early valuable reply!

LM3658 IC image for your reference!

Hello

There is not a batch code or damaged device issues, no know problems with the part.

Device have three version and wanted to make sure all problem parts were the LM3658SD-B (LDO version) which is marked L156B.

Hello
I have this unit working in the lab. With smaller capacitors everything works fine.
But with larger super capacitor size the unit will go into thermal limit and not complete charge. Power dissipation at 0V start up is high and unit will cycle in and out of thermal shutdown but not charge.

1.) Will your problem units overheat?
2.) Do you see a cycling voltage on the output?
3.) Have you measured the charging current?
4.) How large is your super capacitor?

Hello Johns,

For your information, we have 5V ESD protection diode connected on VBAT to DGND.

Please see below inline reply,

1.) Will your problem units overheat? - No
2.) Do you see a cycling voltage on the output? - No, SuperCap voltages steadily increased up to 1.7V (Do you see any voltage cycling at your end?)
3.) Have you measured the charging current?

 - With Li-Ion battery, 50mA for VBAT<3V and 500mA for VBAT>3V

 - With SuperCap, 50mA till VBAT reach 1.7V

4.) How large is your super capacitor?

  - We have checked with 2 different sized SuperCap (0.5mF 5V and 1F 5.5V) - getting the same behavior.

Thanks for your help, looking forward to your reply.

Hello

Can you send a schematic of your circuit?

Regarding item #2 above I should have said current cycling the capacitor will hold voltage during this time. 

Hi John,

Any update? please share your test set-up observations to get more insights into our problem.

Regards,

Jay patel

I looked at this in the lab and our units can charge a SuperCap. Charging current will be limited to between 35mA and 55mA below 3V. 
BUT if the TS pin is open unit is in LDO mode and current is very high.

Is the input current to charger staying at 50mA when the battery voltage stops rising and is it possible the current is going to some other part of the circuit?
The Test Jig set-up with the super cap does it have a 10k resistor on TS simulating the battery NTC?
Input voltage during your test is applied at pin 1 CHG_IN or pin 2 USBPWR?

Hi John,

Thanks for the LAB test results. Please see below inline reply,

1) Is the input current to charger staying at 50mA when the battery voltage stops rising and is it possible the current is going to some other part of the circuit?

- Yes, Icharge = 45mA stays even when VBAT stops at 1.7V

- Yes, possible that current is going to other circuit because rest of the circuit is powered from VBAT only

2) The Test Jig set-up with the SuperCap does it have a 10k resistor on TS simulating the battery NTC? - Yes

3) Input voltage during your test is applied at pin 1 CHG_IN or pin 2 USBPWR? - pin-1 CHG_IN

Extra observations during debugging,

- We have checked SuperCap charging without testjig script (standalone SuperCap connected to VBAT directly)

- observed that VBAT varies between 4.0V and 4.2V (checked 3-times on 3 different faulty boards)

regards,

Jay patel

Hello

I have seen the VBAT variation between 4.0V and 4.2V, see below.  This is the capacitor voltage decreasing to recharge threshold.

See below Start up into a 100mF capacitor.  

The current is limited to about 50mA for the until capacitor voltage reaches 3.0V then fast charge current is applied.