[BQ24166] Charging Comparison between USB500 mode and AC adapter input mode

Are you using a bq24166EVM for this testing?

To what value is the charge current set?  In other words, what is the size of the resistor on ISET?  If ISET is large enough that the IC will be in input current limit mode for USB500 mode but not in current limit when the IN adapter is connected, then the IC will behave differently for each mode.  When both IN and USB are attached, IN takes priority. 

Hello~

Thanks for your reply~

I have additional question in regards to your reply.

As you said that "If ISET is large enough that the IC will be in input current limit mode for USB500 mode but not in current limit when the IN adapter is connected, then the IC will behave differently for each mode."

Would you please let us know the more detail explanation for "behave differently for each mode"??

We need it, because this is end buyer's requirement.

And, we tried to think of one kind of hypothesis.

As you know, charging input conditions are AC adapter as well as USB500.  ISET is setting to 1A.

When it measured the Battery voltage after charging termination, it is different between AC adapter 1A charging and USB500 charging.

- AC adapter charging test: Starting charge current = 1000mA, Battery voltage = 4.1899V
- 1st USB500 mode charging test: Starting charge current = 428mA, Battery voltage = 4.1584V
- 2nd USB500 mode charging test: Starting charge current = 415mA, Battery voltage = 4.1513V

When it saw the results, we are expected as below.

According to the result of experiments,

USB500 mode - Battery voltage is less than minimum value of VBATREG.
AC adapter mode - Battery voltage is between minimum and typical value of VBATREG.

Due to this, When it removes the USB cable after charging termination and then connect the AC adapter, bq24166 is re-keeping the charging condition for a long time (20~30 minutes).

This behavior seems to be affected between VBATREG value and Battery voltage which it depends on different charging mode.

How do you think about that??

With 1-A rated AC Adapter connected (and assuming their is not enough line resistance to cause the voltage at IN to drop to the VINDPM limit), the charger is running in the normal CC/CV mode and should charge at the full 1A charge current.

With USB500, the charger is initially running in input current limit mode instead of CC mode and so the charge current will be reduced from the 1A limit.  The control loops are analog so the exact value of charge current when the various analog control loops take control, will vary slightly from test to test.

In either case assuming no line resistance, charge will terminate when the battery voltage as measured between the IC's BAT and GND pins is above VBATREG-VRCH and ICHRG < ITERM.  Line/connector resistance between the battery and BAT/GND pins and the battery's own internal resistance could cause the charger to terminate when the battery voltage is VBATREG - VRCH - VRES where VRES =10%*ISET*(RLINE+RBAT).

All of the above assume that you do not enough load on SYS to force the charger into a mode other than CV at termination.  If in another mode (input current limit or VINDPM or thermal regulation), then termination is disabled and the IC will not terminate.

For the battery voltages above:

1.  Were those voltages measured as close to IC BAT and GND pins as possible after charge termination?

2.  Was the same battery or battery simulator as well as connections used each time (i.e., having the same line/connector same resistances)?

I tested an EVM using a Keithley 2420 as battery simulator and see the same battery termination voltage whether powering from IN or USB500.

Hello~

Thank you for your kind support~

Due to your good answer, almost all issues have been resolved.

I hope this will be my last question for this issue.

-1-  Answers for your questions

(1) Were those voltages measured as close to IC BAT and GND pins as possible after charge termination?
    --> After charging was completed, it measured the voltage at the +,- terminal of battery pack.

(2) Was the same battery or battery simulator as well as connections used each time (i.e., having the same line/connector same resistances)?
    --> It measured the voltage that is using the same battery on the same PDA.

-2- Additional questions

As you know, charging input conditions are AC adapter as well as USB500.  ISET is setting to 1A.

(1) I'd like to know what is the condition to be set to the Minimum or Maximum value of VBATREG. (ex. Temperature high -> Maximum, etc...)

(2) If input current is devided by the current for charging (400mA) and for load (100mA) at the USB500 mode, Would this condition be impact the charging termination condition??

(According to your answer, you seems to be allocated the whole 500mA to the battery (or battery simulator) when you tested with EVM. But, in real system, limited 500mA input current is split to system load and battery charging, even if system is idle mode.)

(3) As described above, if BQ24166 is operating with the degree of 400mA charging current at USB500 mode, Does Charging Termination function is also working properly??  Or, As our test results, Would it be happen the symptoms such as the lower Charged Voltage??

Thanks... C.W. :)

Regarding 1, for the bq24166, VBATREG is always 4.2V.  When the temperature is too hot (>60C) or too cold (<0C), the charger stops charging.

Regarding 2 and 3, if any control loop other than constant voltage is in control at termination(VBAT>VBATREG-VRCH and ICHARGE<ITERM), then termination is disabled.  For example, if your system load + termination current > what the input current limit will allow, thereby activating the the input current control loop, termination will be disabled and the IC will provide whatever charge current is available to maintain the battery voltage as close to 4.2V as possible.

Is the 360 minute safety timer expiring?  That will cause early termination.