BQ24650 6mA discharge current issue

Seems like the part is not getting into sleep mode.

Q1 the top switching FET may be one trying to deliver charge and allows the battery and Vcc to be within 100mV and not go into sleep mode.

Try putting a schottky diode in series with VCC just before the 10 ohm filter resistor and see if this solves your issue.

Another was is to put a heavier load on your input so the input voltage drops with the 2mA source...This may put the part in sleep mode.

Hello TI,

Similarly, I have a problem -6mA.

<Board>
BQ24650EVM

<changing point>
MPPT : 9.3V
At VFB=2.1V, CAP voltage is 3.75V
The other circuits are default.

Battery: LiIon-capacitor (2.2V-3.8V)

<situation>
The starting voltage of CAP is 3.0V.
I will increase little by little VIN by DC-Power-Supply.
Current Meter is between Vout and CAP+.
The sign of current, sign + implies charging to CAP from EVM.

(1)VIN < approx. 3V
VOUT current = approx. -50uA
STAT1 = OFF, STAT2 = OFF

(2)VIN > approx. 3V
VOUT current = approx. -370uA
STAT1 = OFF, STAT2 = OFF

(3)VIN > approx. 4.5V not sleep
VOUT current = approx. -6mA ( Battery detection? )
STAT1 = ON, STAT2 = OFF

(4)VIN > MPP
　VOUT current = approx. +2A(max)
STAT1 = ON, STAT2 = OFF

<Question 1>
I want to avoid -6mA at (3).
I experimented by putting a diode between the EVM and battery.
As a result, -6mA issue disappear, but the battery voltage is not stable at charging.
Also there is another Di energy consumption issue.

I'm glad if you can tell me that there are some counter measures.

<Question 2>
For -6mA problem, I'm thinking the way to perform EVM-shutdown at the condition (VIN <MPPSET).
So, Is there any way it can be determined with definitly the state of the condition (MPPTSET> = 1.2) ?
( except external comparator )

Thank you.

Hi,

I've had this exact same problem for over seven months now.  I put this work off for a long while to do other things but now I must solve it once and for all.  I have a topic opened about it that got ignored and then hijacked here:

http://e2e.ti.com/support/power_management/battery_management/f/179/p/223725/822899.aspx#822899

I just tried this idea of putting a schottky diode in series with the 10 ohm resistor to VCC but it didn't change anything.  I've started working with comparators to try and make this work. 

The problem is that the BQ24650 goes to sleep fine when the voltage drops below Vmpp (based on comparator setup) but then immediately pops back on when solar panel goes to Voc and releases comparator's OFF state.  Then the BQ24650 tries to charge again and immediately the solar voltage drops and it turns off.  This continues while the cloudy condition does, which is no good.

My current efforts are to consider hysteresis, but the problem there is that setting 'the return to ON' voltage too high could keep the charger off when there is enough sunshine to charge but not the right point for the comparator to be smart enough to know when it is Voc or loaded.  I will be continuing to work on this but if there is another way to do this that TI can share, I would love to read it.

Thanks,

Mike

Hello,

Thank you for the comment very helpful. I agree.
As you say, I guess there is an difficulty adjusting switching-thresh.

I'd like to expect this issue will be handled essentially by TI.

 Thank you.

Hi folks, I'm glad so many people responded  to my thread. It seems the problem still has no easy solution. Can anyone determine where does the current drainage occur? I suspect the SRN pin does it. 

Hello!

Basically, I have the same critical mind. And, I'm suspecting "battery detection feature".

Thank you.

There's information I did not share earlier, I contacted a TI support engineer and here's the email conversation between he and I...

-----Original Message-----

From:  TI
Sent:  5/6/2013 07:48:53 AM
To:  
Subject:  RE: Re: SR#1-985507253.

Hello York,

The idea is to place the diode in order to avoid battery getting discharged through the body diode of the top FET back to the Vcc of the IC.

Please respond with your observation after placing the diode in series with drain of MOSFET.


Thanks & Regards,

TEXAS INSTRUMENTS

Please Note:
"TI assumes no liability for applications assistance or customer product 
design. Customer is fully responsible for all design decisions and 
engineering with regard to its products, including decisions relating to 
application of TI products. By providing technical information, TI does not 
intend to offer or provide engineering services or advice concerning 
Customer's design. If Customer desires engineering services, the Customer 
should rely on its retained employees and consultants and/or procure
engineering services from a Licensed Professional Engineer ("LPE")."
[THREAD ID:1-GAQU9Z]



-----Original Message-----

From:  
Sent:  4/28/2013 10:56:26 PM
To:  TI
Subject:  Re: SR#1-985507253.

Excuse me, but I don't quite understand what you mean by " moving the diode 
down stream of the RC across Vcc". In the attached schematic, are you 
suggesting putting a diode 'D3' there?

Thank you
York

-----Original Message----- 
From: TI
Sent: Friday, April 26, 2013 7:25 PM
To: 
Subject: RE: Re: SR#1-985507253.

Hello York,

Try moving the diode down stream of the RC across Vcc.  This will put the 
device into sleep mode ~0.5V sooner, though not sure if it will matter much 
since we want it to operate at the MMP which is typically 80% of Vin_OC.

But please try the same once and then acknowledge with your observation.

(Apart,I mistook your first name as Lei, because the contact column in 
Customer detail's reads out as 'Lei Miao'. Though, sorry for misinterpreting 
it.)

Thanks & Regards,

TEXAS INSTRUMENTS

Please Note:
"TI assumes no liability for applications assistance or customer product 
design. Customer is fully responsible for all design decisions and 
engineering with regard to its products, including decisions relating to 
application of TI products. By providing technical information, TI does not 
intend to offer or provide engineering services or advice concerning 
Customer's design. If Customer desires engineering services, the Customer 
should rely on its retained employees and consultants and/or procure
engineering services from a Licensed Professional Engineer ("LPE")."

[THREAD ID:1-GAQU9Z]



-----Original Message-----

From:  
Sent:  4/24/2013 07:43:17 PM
To:  TI
Subject:  Re: SR#1-985507253.

Hi TI,

First of all, thanks for taking time solving this problem. I am very
grateful.
The schematic is attached to this email, also contained is the 3.3V Buck
converter, which works fine.

Thanks again for your efforts.
Best regards.
York

PS, I don't know where did you find the information to address me as "Lei",
neither do I nor my colleagues are called "Lei". But that's fine, you can
call me Lei as my nickname.

-----Original Message----- 
From: TI
Sent: Wednesday, April 24, 2013 11:19 PM
To: 
Subject: RE: RE: SR#1-985507253.

Hello Lei,

I have communicated you issue to concerned team, and hopefully they will
respond me soon, on to which I will update you.
In the meanwhile, please provide the schematic of your circuit.

Please acknowledge.


Thanks & Regards,

TEXAS INSTRUMENTS

Please Note:
"TI assumes no liability for applications assistance or customer product
design. Customer is fully responsible for all design decisions and
engineering with regard to its products, including decisions relating to
application of TI products. By providing technical information, TI does not
intend to offer or provide engineering services or advice concerning
Customer's design. If Customer desires engineering services, the Customer
should rely on its retained employees and consultants and/or procure
engineering services from a Licensed Professional Engineer ("LPE")."

[THREAD ID:1-GAQU9Z]



-----Original Message-----

From:  
Sent:  4/11/2013 07:08:27 AM
To:  TI
Subject:  RE: SR#1-985507253.

i still have not solved this issue. The chip will discharge current from the
battery when the sunlight is dim but not completely black. I have 2
prototype boards and they behaves the same.

Date: Thu, 4 Apr 2013 05:02:17 -0500

From: TI

Subject: SR#1-985507253.

To: 

Hello Lei,

TI Technical Support has received your email.

We have created a service request with reference number #1-985507253.

Please refer this number whenever you want to enquire about this issue. We

are currently working on this issue.

We will get back to you as soon as we find some relevant suggestions.

Please be sure we will do our best to help you ASAP.

Till then we request you to hold on. Kindly note that in all your

responses do not delete the thread ID. This will help your responses to

reach us in time.

Thanks for your understanding and patience.

Thanks & Regards,

TEXAS INSTRUMENTS

Please Note:

"TI assumes no liability for applications assistance or customer product

design. Customer is fully responsible for all design decisions and

engineering with regard to its products, including decisions relating to

application of TI products. By providing technical information, TI does

not intend to offer or provide engineering services or advice concerning

Customer's design. If Customer desires engineering services, the Customer

should rely on its retained employees and consultants and/or procure

engineering services from a Licensed Professional Engineer ("LPE")."

[THREAD ID:1-GAQU9Z]

-----Original Message-----

From:  

Sent:  4/3/2013 12:47:36 AM

To:  TI

Subject:  BQ24650 6mA discharge current issue.

  Hello,   I’m using BQ24650 to charge 4 LiFePO4 batteries in series

(14.4V) with  power supplied by solar PV panel. The MPPSET point is set to

17.2V, according to  the PV panel’s spec.   Well after much effort the

charger now works pretty fine as expected,  except when at very low

sunlight, the BQ24650 starts draining  power from the batteries instead of

charging them. The current drained is  measured 6mA constantly, the

voltage of the PV panel is measured approximately  15V at this time, and

current from PV panel is about 2mA or so.    However the discharging

current will stop when sunlight is completely  removed.     How can I

eliminate this discharge current? As 6mA power drain is quite  undesired.

And I suspect the battery detection procedure within the BQ24650 is

causing this drainage.   Thanks very much if anybody can help me out of

this.   Best regards. York

Hi,

I just tried moving this extra schottky diode from being in series with the 10 ohms resistor after the solar panel's blocking diode (called D1 on the EVM) to before it.  That way the only forward voltage possible to VCC was from the solar panel.  Unfortunately, that prevents charging from happening at all.

I was surprised that prevented charging all together but maybe I shouldn't be because there must be some kind of feedback from the power FET when it is on and this blocks that.  Still waiting on parts for my hysteresis testing but looks like my only option at this point.

Michael

Did you guys tried putting the schotky diode just before the upper FET 's drain? As TI engineer Varun informed me to do so but I am on vacation and couldn't do the test. 

Thank you.

Please let me know if you have tried the following configuration and the results.  See attachment.

Hi Charles,

We've just did the experiment, placing a diode just before the FET as the attachment instructed. It has no effect, the BQ24650 will still discharge 6mA from the
battery when VCC is below MPPSET voltage. Now I'm sure the 6mA drainage is going thru SRN pin.

The chip will charge normally at maximum current set by the resistor between SRN and SRP.

Please confirm this information if you have the same result, even with BQ24650 evaluation board. Thank you!

Thanks for the feedback, I did not expect that.

What state are the low and high side drive in (high, low or switching).

Do you have any loads on the drives that could be pulling current?

Can you measure the 6mA discharge through the sense resistor?

I will see if I can contact the design to get any more insite.

Please attach your schematic so I can see if there are any differences.

There is a ~6mA discharge current when the part is enabled, so one has to disable the IC.

For your information Charles, I modified the circuit to charge only one 4.2V Li-ion battery (see attachment) and I measured following conditions when the leakage happens -

1. MPPSET voltage is set to 6.1V while VIN is given 5V

2. Both high and low side FET are off, VGS < 0.1V

3. All loads to other circuit are completely cut off.

4. Total current draw from battery is measured 6.4mA, the voltage across 0.047R sense resistor is 15mV, so current thru it is 3.2mA.

5. Although i can not measure current thru the inductor and FETs, it can be deferred there's no current. Because (a), VIN(5V) is higher than VBAT(4.2V), and (b) FETs are all off, there can't be current thru it.

So i conclude current is going thru both SRN and SRP pin, about half each.

Attached is a solution to the shaded solar panel application.

Hello,

Thanks for official comment.
I tried that method before. however, charging-voltage was oscillating, by adding Schottky Diode before feedback signal.
 ( diagram is same as "How to Design BQ24650 Under Shade Condition" )

FYI, my target battery is LiC Super-Capacitor 10000F.
Is there method suitable for these battery ?
I'd appreciate your any advice.

Thank you very much.

I am not totally sure how the bq24640 is different than the 650.  You may try that part since it is identified as a super cap charger.