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Original question:

BQ24196: Regulated power path output, without disturbing battery

BQ24195L: BQ24195L not charging

Ole Kristian Western
Prodigy 85 points

Part Number: BQ24195L
Other Parts Discussed in Thread: BQ24195

I have designed a circuit with BQ24195L that will not charge. System pin outputs about 4.1V when VIN is 13.5V, and drops to Li-Ion (3.7V) when 13.5V is disconnected, so it's at least doing something.

I have followed the Typical Application on page 34 of the datasheet, but omitted Q1/Q2 circuit, Q3/R11.  OTG is not used and floating.

Inductor is a 2.2uH (3.3A, 68mOhms DCR).

NTC 10k with 5.6k/33k resistors.

I feed it with 13.5V and have a single cell connected.  Charge enable is pulled low.

I have read all the registers and see all conditions are ok, for example REG01[5:4] = 01. Watchdog kicks in after some time.

I also see the battery is fed (charged?) 82mA, but in pulses. Cycles between 82mAfor around 2-3 second, then drops to 0mA for a few seconds.

Do I have to set / start something at first time use? Or could the pulsing be a sign that the buck can't start properly (DRC or other spec of the inductor not compatible with bq24195 spec)?

  • 0
    TI__Mastermind 33360 points

    Hello, 

    Can you help to share a waveform showing SW node while you attempt to charge so we can confirm if the buck converter is functioning properly? It would also be helpful if you can share what all registers read while attempting to charge so we can review. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    Sorry for the late reply. I didn't get any notifications. Not I'm out of the office until Wednesday. I'll get back to you.

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hello, 

    Understood, thank you for providing an update. 

    Best Regards,

    Garrett 

  • 0
    Prodigy 85 points

    Here are the DC and AC on SW node. 

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hi Ole, 

    In general the SW node voltage looks correct. Can you confirm what the input voltage was when you captured this waveform? In your initial post you said your Vin = 13.5V, but based on waveform that does not appear to be the case, VIN looks to be ~5V. 

    Based off your description of the behavior and the provided SW node waveform the buck converter appears to be functioning. For the next step of debug it would be helpful to review the status of all registers when you are attempting to charge, as well as, provide voltage measured at BAT pin of IC while you are attempting to charge. 

    Ole Kristian Western said:
    I also see the battery is fed (charged?) 82mA, but in pulses. Cycles between 82mAfor around 2-3 second, then drops to 0mA for a few seconds.

    Based off this description I am wondering if your battery is simply approaching full charge. Do you observe the same issues if you further discharge your battery?

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    VIN was 13.5V. Both waveforms are of SW node, not VIN (first is DC, second is AC).

    Is it normal that it pulses like that when battery is closing to fully charged?

    I tried with many batteries, but maybe they were all full(?).

    I'm trying to find a discharged battery and test.

  • 0
    Prodigy 85 points

    REG00: 0x30 (100mA IINLIM)
    REG01: 0x1B
    REG02: 0x60
    REG03: 0x11
    REG04: 0xB2
    REG05: 0x9A
    REG06: 0x03
    REG07: 0x4B
    REG08: 0x34 (VBUS_STAT unknown (5VDC measured on VBUS), charge termination done (battery only 3.8V)).
    REG09: 0x80 (Watchdog timer expiration)
    REG0A: 0x23

    Not sure why is is "charge termination done", since battery is only 3.8V and NTC is 25'C.

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hi Ole, 

    Thank you for providing the requested information. REG08 indicating charge termination done and no other faults is the key status to understanding the behavior you are observing. The BQ24195L appears to be operating correctly. The charge current to the battery cycling between a few seconds at ~ 80mA and a few seconds at 0mA matches expectation for a battery which is reaching termination condition then a few seconds later starting a new charge cycle. 

    Now I do not know the specifics of your design, but given the information that battery voltage = 3.8V it appears your system has some voltage drop along the path from BAT pin to the actual battery terminal. The BQ24195L device determines the phase of charge it is operating in based on the battery voltage it measures at BAT pin. The device has no way of knowing the actual battery terminal voltage when there is a voltage drop along the path.  

    What appears to be happening is BAT pin voltage is measured at approx. 4.2V once current is flowing to the battery leading to charge termination.  If you are able to reduce the battery voltage so BAT pin voltage is < 4V during charging I expect you to observe steady charge current to the battery. 

    You mention you have tried with multiple batteries, you can also use a battery simulator such as a Keithley sourcemeter instead of a real battery to verify the charger IC is functioning properly. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    I measure 4.045V at BAT node and 4.066V at battery terminal when 12V is disconnected. So there is negligible drop. When I connect 12V it increases to 4.071V at BAT node when NTC is floating (no sensor). Then I connect a 10k resistor (to simulate 25'C), BAT node increases to 4.101V. It's charging with 40mA.

    I tried with a 2.7V battery and charge only increased to 64mA and BAT node was 2.85V.

    We sadly don't have a sourcemeter at hand.

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hi Ole, 

    The observed voltage drop will increase as current flowing from BAT pin to BAT terminal increases. Therefore I expect the measured voltage drop would be more significant when the device attempts to charge at higher ICHG setting. 

    Ole Kristian Western said:
    BAT node increases to 4.101V. It's charging with 40mA.

    In this scenario is charge current stable? If so then the device is charging as expected considering your input current limit is set at 100mA.

    Ole Kristian Western said:
    I tried with a 2.7V battery and charge only increased to 64mA and BAT node was 2.85V.

    Similarly the device appears to be functioning correctly when you attempt to charge the battery with VBAT = 2.85V. The charge current will not be much more than 100mA with your input current limit set to 100mA. If you have any current draw at SYS it will cause charge current to reduce further. Hence, 64mA charge current is within reason. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    Isn't the input current limit in respect to VBUS (in my case 12V)? At the moment it's drawing only 23mA from the 12V supply (which is reasonable with 64mA charge (12V*23mA/4.2V=65.7mA minus efficiency loss)). Shouldn't it at least max out the input limit (100mA) when the battery is so low, before limiting (which should charge with 285.7mA (12V*100mA/4.2V)? And the draw on SW node shouldn't affect the charge fed to the BAT node? It should at least have two settings, one system draw, and one battery charge. It would bug me if the battery charge rate is completely dependent on how much the system draws, when I have "unlimited" (3A) VBUS supply.

    By the way, the input current limit is 1.13A (1/470*530) in resistors and 3A (0x37 in REG00) when booting, but drops immediately to 100mA (0x30) when I apply 12V to VBUS.

    I read the register REG02 (ICHG) to default (0x60), 1536mA.

    By the way, I think there is an error in the datasheet. It says default REG02[7:2] is 011000, which is 2048mA, but 011000 comes out to 1536mA (1024+512).

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hi Ole, 

    Please see my comments below. 

    Ole Kristian Western said:
    5VDC measured on VBUS

    In a previous response where you shared the register statuses from the device you mentioned you measured 5V at VBUS. Unless that measurement is incorrect it seems your system has a component on the input side of the BQ24195L which is converting the 12V supply down to 5V. Assuming this is the case the charger IC only has a 5V*100mA at the input. 

    Ole Kristian Western said:
    And the draw on SW node shouldn't affect the charge fed to the BAT node? It should at least have two settings, one system draw, and one battery charge.

    When IINLIM is set to 100mA it is limiting the input current to the buck converter. Both SYS and BAT are connected to the output of the buck converter. If you only want to limit charge current without limiting current draw at SYS output you should be changing ICHG register and setting IINLIM to a larger value.  

    Ole Kristian Western said:
    By the way, the input current limit is 1.13A (1/470*530) in resistors and 3A (0x37 in REG00) when booting, but drops immediately to 100mA (0x30) when I apply 12V to VBUS.

    The input current limit will be the smaller values between the resistor setting and the register setting. The observation of REG setting dropping to 100mA indicates the D+/D- input type detection is setting IINLIM to 100mA. In the short term for testing you should be able to overwrite this by writing to REG00 after 12V supply is connected. 

    Ole Kristian Western said:
    By the way, I think there is an error in the datasheet. It says default REG02[7:2] is 011000, which is 2048mA, but 011000 comes out to 1536mA (1024+512).

    There is not an error in the ICHG register. There is a 512mA offset as indicated in the REG02 table note column. 011000 will be 2048mA (1024+512+512 offset). Even if all bits are set to 0b ICHG = 512 mA due to the offset. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    Thanks for a very good reply. Silly me, forgot to mention the 5Vout buck before bq24195 VBUS.

    Seems the D+/D- input type detection messes up things. I'll override it for now, but do you have any idea why it happens? D+/D-/OTG/PMID are all floating, 

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 33360 points

    Hi Ole, 

    When D+/D- are floating the device will detect the input as unknown and set input current limit to 100mA. This is shown in Table 2 on page 14 of the BQ24195L datasheet. The table also shows all possible current limit settings given the D+/D- detection (100mA, 500mA, 1.5A). 

    Given that your design does not intent to use the D+/D- pins I recommend you adjust your firmware to always overwrite the input current limit after input is applied. This can be achieved by repeatedly writing the desired IINLIM value to REG00 or your host MCU can monitor PG_STAT in REG08 to know when an input source is applied. 

    You can also test if shorting D+/D- pins together rather than leaving them floating results in the input current limit being set to a higher value than 100mA. This strategy works on some of our newer charger devices, but I have not been able to confirm if the same applies to the BQ24195L.  

    Best Regards,

    Garrett