bq2002 - charging and termination

Thanks Chris.

I can understand more clearly in Battery charger.

Now I'll test with DV2002L2 EVM.

I have one question.

As I know TS pin is sensing the battery temperature.

If TS pin is lower than Vtco(0.5*Vcc), the charger will occur termination. Right?

But as shown DV2002L2/TL2 Board Schematic, R5(RT1), R18(RT2) value is strange.

The thermistor(10K) and R18(RT2) is parallel circuit.

So TS Pin is always under the Vtco.

How can I calculate the R5 & R18?

Plz let me know.

Thanks.

Best Regards.

Harry

The DV2002L2 contains the bq2002 IC, while the DV2002TL2 contains the bq2002T IC.  All of the bq2002 ICs have different parameters which are summarized here: http://focus.ti.com/lit/ug/sluu229/sluu229.pdf

The schematic shows the bq2002T setup.  My guess is that the resistors are different for the bq2002, but I will check.

thisis the link to the UG:

http://camus.itg.ti.com/pdf/sluu007a.pdf

 Fixing the broken link: http://www.ti.com/lit/ug/sluu007b/sluu007b.pdf is the correct link

For the DV2002, not the T version, R18 is open and R5 is a 3.57k.  With a 10k thermistor, this keeps you above the 0.5*Vcc TCO voltage.

We will be updating this UG shortly to reflect this difference.

Thanks for your reply Chris & CHM5.

BQ2002T Vtco is 0.225*Vcc. It's defferent with BQ2002(Vcto = 0.5 * Vcc).

So I think the calculate is based on the 0.225*Vcc.

Now I have one more question about TM pin.

As shown by the BQ2002 datasheet,  TM pin can control fast charge current rate with C/2,C,2C.

I changed the TM pin with Vcc,Vcc/2 & GND,  but charge current is not change.

What is the mean "C"?

 Best Regards.

Harry.

I agree that this is a little confusing.  The C rate is the pack rating--a 750mAhr pack has a C rating of 750 mA.  1C is what current the pack must be charged at (at 100% efficiency) to complete charge in 1 hour.

The bq2002 does not monitor the charge current at all.  It simply applies or restricts current to flow, by operating the CC output.

The TM pin is a timer mode input.  It really only adjusts the fast charge timer--80 min for 1C, 160 for C/2, etc.  It assumes the user will adjust the charge current to charge at the stated rate.  Since the IC has no knowledge of the charge current, it cannot adjust it.

The charge time must be adjusted for different charging rates to assure that fast charge will complete before the timer expires.  Note that for 1C charge rate, the timer is 80 minutes.  Charging nickel cells is not 100% efficient, so even though you are charging at a 1C rate, it will take longer than 1 hour to fully charge the pack.  80 minutes is an industry standard charge time at a 1C rate.

Chris, you are obviously very knowledgable about the bq2002, but I have some questions about some of the responses you have given above:

1. Youi note that there are three ways of detecting that a battery is fully charged, including rate of change of temperature dT/dt.  However, I can't see anything in the bq2002C datasheet about rate of change of temperature.  Does it terminate fast charge if the battery temperature starts to rise?
2. The bq2002C datasheet specifies the High Temp Cutoff Voltage as 0.5*Vcc and the High Temp Fault Voltage as 0.6*Vcc, but they don't appear on the State Diagram, so it is not obvious that they influence the state transitions. http://focus.ti.com/lit/ug/sluu229/sluu229.pdf defines the values for different variants of the bq2002 family.  For the bq2002T which is fitted on the DV2002 board they are 0.225*Vcc and 0.25*Vcc respectively.  The thermistor manufacturer datsheets can be used in conjunction with the resistor values fitted to the board to calculate the temperature thresholds designed into the board.  These work out as a High Temp Cutoff of 52 deg, and a High Temp Fault of 46 deg.  The description given in the bq2002C datasheet for the High Temperature Fault therefore expands as "Temperature greater than 46 deg inhibits fast charge start".  Similarly the description for Temperature cutoff expands to "temperature greater than 52 deg inhibits/terminates fast charge".  Would I therefore be correct in assuming that (a) Fast Charge will not start if the battery temperature exceeds 46 deg (b) In addition to the conditions stated in the State Diagram Fast Charge will also terminate if the battery temperature exceeds 52 deg (c) the bQ2002 does not monitor the rate of change of temperature?
3. The bq2002C datasheet makes brief reference to "top-off phase", but doesn't define it. http://focus.ti.com/lit/ug/sluu229/sluu229.pdf states that the bq2002C has no top-off charge rate.  Should the references in the datasheet therefore be deleted?

1.  Not all nickel chargers look for all 3 termination evidences.  The bq2002C does not look at dT/dt for termination, per table 1.  Here is a report that shows the difference between the bq2002's including how they terminate fast charge: http://focus.ti.com/lit/ug/sluu229/sluu229.pdf

2.  Yes, you are correct on all counts.  The state diagram does show Vts levels as a way to move from state to state.  This is further explained on pages 4, 5, and 6.

3.  Right again.  I'll see about updating the datasheet.

Dear charles,

Could you pls give me this sluu007a.pdf file?

I could not download below weblink...

http://camus.itg.ti.com/pdf/sluu007a.pdf

And I have a question of charger for using EVM(DV2002L2/TL2) with bq2002 ?

I will use two series NiHM,

one NiHM is 1.2V/1000mA, Total of two is 2.4V/1000mA.

In order to charge of  two series NiHM,

Is It possible to use without(remove) LM317?

If have, Pls let me know ASAP..

Best regards,

eric@semidj.com

If you remove the LM317 (costant  current source)

how do you charge the battery pack?

I'm not surely understand the bq2002 function..

And worried about PCB size...

Frtunately LM317 has SMD package..

any how thanks for your comment...

The LM317 is a costant current source.

The current in the battery pack is 1.25V divided by R7

The signal (digital) provided by CC turn off/on the current source by the BJT.