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BQ25600: how to understand the spec in JEITA THERMISTOR COMPARATOR?

Brian Li
Genius 9685 points
Part Number: BQ25600

Hi team,

My customer is using our BQ25600.

And they find below table.

Could you please kindly help check if we have the data for 55 degree?

And please also help explain how to understand this falling?

And please also help check how to understand the 4.2V and 4.05V in Charge back to ICHG/2 and 4.2 V, Charge back to ICHG and 4.05 V?

Thanks,

Brian

  • 0
    TI__Mastermind 33935 points

    Hello Brian,

    The values VT1, VT2, etc. correspond to a voltage on the TS pin and the charger changes behavior based on whether or not the TS pin is the corresponding certain percentage of REGN. The charger does not explicitly know the temperature of the battery, it knows how to read the TS voltage impacted by the thermistor from the battery. As such the temperature voltage thresholds for 55C are not captured and depend on bias resistors and chosen thermistor. The voltage thresholds of the TS pins in the provided image of the datasheet hold however.

    "Falling" corresponds to the hysteresis on the TS pin. Please treat the "Falling" for VT3 and VT5 as rising threshold hysteresis.

    Between T1 and T2 the customer has the option to change the charge current to half or 20% of the programmed value. Between T3 and T5 the charge voltage can be changed to 4.05 V or full charge voltage regulation.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Genius 9685 points

    Hi Mike,

    Thanks a lot.

    And here's still five questions need your comments:

    1. When it is 55 degree, what is the voltage threshold of TS pin?
    2. Customer find that we directly connect the PSEL pin with REGN pin, why we choose this kind of connection, is it only want to connect to GND?
    3. Customer will use 2 battery with each battery 220mA, will this 500mA current limit have any risk?
    4. How to understand the host mode? Do they need to set some register to go into host mode? 
    5. Can they connect the PSEL to GND and set the register to High? 

    Thanks，

    Brian

  • 0 in reply to Brian Li
    TI__Mastermind 33935 points

    Hi Brian,

    1. As mentioned earlier, the TS pin does not measure temperature it measures voltage. The voltage on the TS pin will vary depending on thermistor and chosen bias resistors.

    2. Please read the PSEL pin description, "Power source selection input. High indicates 500 mA input current limit. Low indicates 2.4A input current limit. Once the device gets into host mode, the host can program different input current limit to IINDPM register."

    3. Are you intending to charge two batteries in parallel? What is the recommended charge current for each? Do you intend to have a system load? 

    4. Please read Section 8.3.5.1. The device can be used without I2C registers in default state. However for custom charge current and other features, I2C host communication is needed.

    5. Yes the input current limit can be set high after getting into host mode. See Question 3. 

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Genius 9685 points

    Hi Mike,

    When the T=55℃，What is the percentage to VREGN of 55℃ threshold and Falling like below?

    Michael Emanuel35 said:
    3. Are you intending to charge two batteries in parallel? What is the recommended charge current for each? Do you intend to have a system load? 

    They will connect two battery in parallel an charge them at the same time, each battery's capacity is 220mAh and there's also system load when the battery charging. Please refer to below battery spec. Will the 500mA limit have any risk?

    Thanks,

    Brian

  • 0 in reply to Brian Li
    TI__Mastermind 33935 points

    Hello Brian,

    As mentioned before, it will depend on thermistor and bias resistors. We do not spec 55C.

    Please charge according to your application. Make sure the total charge current to each battery does not exceed the max charge rate in your battery spec during all modes of operation. A 500 mA input current limit could be an issue depending on how much system load there is. If the input current limit of 500 mA is reached, charge current will be reduced to support the system.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Genius 9685 points

    Hi Mike,

    Can BQ25600 monitor the temperature ?

    If not, do we have p2p device have this function?

    Thanks,

    Brian

  • 0 in reply to Brian Li
    TI__Mastermind 33935 points

    Hi Brian,

    As I stated before, the TS pin does not measure temperature directly but through a voltage related to the thermistor resistor depending on temperature. I encourage you to read Section 8.3.7.4 of the datasheet. In there you will see that TS is biased as a voltage divider with a pullup resistor and a parallel resistor with the thermistor. As the temperature on the thermistor changes, the resulting TS voltage will change. The thresholds given below indicate at what voltage VT1, VT2, etc. will occur at relative to REGN. The reference for the temperature is only valid if a 103AT thermistor is used with 5.23kOhm pullup and 30.9kOhm parallel resistor. As a sanity check, a 103AT measures 27.28kOhm at 0C. Parallel combination is 14.5kOhm, and % of REGN is 73.5% as shown in VT1.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Genius 9685 points

    Hi Mike,

    Here is the battery recommend charging current and voltage:

    And here's the NTC resistance for the five temperature:

    Can they use the RTHHOT=RTH55℃=27.09K to calculate RT2=194.1K, RT1=45.7K as below?

    They want to make the battery 55℃ to trigger the VT5 charging setting and 42℃ to trigger VT3, and then 0℃, 10℃ trigger VT1 VT2.

    Could you please kindly help check if customer's solution is OK?

    Thanks,

    Brian

  • 0 in reply to Brian Li
    TI__Mastermind 33935 points

    Hi Brian,

    I cannot comment on the battery specification because it is not clearly written with regards to punctuation and the use of "min Max." back to back.

    I have verified that at 55 C the % of REGN will be 34.2% at VT5, at 45C the % of REGN will be 42.5% slightly below VT3, at 10 C the % of REGN will be 68.8% at VT2, and at 0 C the % of REGN will be at 73.3% at VT1. The selected resistors should work.

    Regards,

    Mike Emanuel