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BQ24196: Regulated power path output, without disturbing battery

Ole Kristian Western
Prodigy 85 points
Part Number: BQ24196
Other Parts Discussed in Thread: BQ25303J, , BQ24192, BQ24193, BQ24195L, BQ24192I, BQ24190, BQ25606

I have a question about pulling system power directly from a switching battery charger (not through the battery).
I need Vout=4-5.5V, Vin=12-15V (could vary), and 1 cell 4.2V li-ion battery backup in case Vin is disconnected.
In normal mode (Vin present) it should output 3.5-5.5V directly from it's buck (not through the battery).
I see many bq2xxxx have 3.5-4.35V on either SYS or SW pin. Will pulling (50-400mA) from this, disturb the battery charge sensing (since the SW / SYS pin voltage will drop with the external consumption)? I would hate "ripple" charge/dischage, due to the consumption. I would like the battery to be as disconnected as possible, just waiting for Vin to disappear.

The 12V will be able to supply enough for both charging and consumption, so no load sharing.

I have been looking at these:
bq25303J, bq24195L, bq24193, bq24190 / bq24192 / bq24192I, bq24196.

Standalone is a good safety measure, but I will also enable control it from an MCU + i2c bus and shunt voltage monitor.

Would all be good choices?

  • 0
    TI__Mastermind 28650 points

    Hello, 

    Thank you for reaching out via E2E. First, The BQ25303J has a different architecture than the rest of the devices you listed.  All other devices you listed are narrow VDC (NVDC) architecture where BATFET separates the system from battery. Each devices datasheet should have a section to further explain NVDC.  This is not the case on the BQ25303J where there is only one output from the buck. Due to your desire to have battery as disconnected as possible I would not recommend the BQ25303J. 

    On the BQ2419x devices pulling 50-400mA at SYS will not be an issue. 

    The NVDC architecture allows you to set the minimum system output voltage when Vin is present via I2C. Please note we do not have a single cell charger where minimum system voltage can be set to 4V or greater. For example, on the BQ2419x device max SYS_MIN setting is 3.7V. When battery is above SYS_MIN threshold SYS voltage will follow the battery and then when battery is discharged SYS voltage will be regulated at the SYS_MIN setting. For example, when your battery is fully charged SYS will be regulated at 4.2V. 

    Therefore if your design requires Vout at sys pin to always be above 4V you likely need a 2 chip solution. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 85 points

    Thanks for your answer. Actually sys doesn't have to be above 4V. It shall power a 3.3V LDO, which should work fine with 3.7V or even lower. 

    I needed to put a 40V tolerant automotive buck (AP64352QSP-13) between the 12V and the bq2xxxx (to make input protection easier), so Vin of bq2xxxx is now 5V (can be changed to anything higher if it makes the overall system more effective).  And anything I should be on the lookout for when I connect the buck and bq2xxx in series (frequencies, resonance, etc)?

    I've limited my choices to bq25606 and bq24195L. For bq24195L, page 34 of datasheet (9.2 Typical Application). Can I omit the whole Q1/Q2 circuit (since it's connected directly to the 5V buck)? And if no need for OTG, also Q3/R10/R11, and pull OTG to ground via 10k?

  • 0 in reply to Ole Kristian Western
    TI__Mastermind 28650 points

    Hello, 

    There is no issue with having a buck part that outputs 5V before the battery charger IC. 

    The BQ25606 and BQ24195L are relatively similar, with the main difference being that BQ25606 is standalone and BQ24195L is I2C controlled. 

    Please see below for comments on your questions regarding BQ24195L typical applications. 

    -The Q1/Q2 circuit shown on page 34 is for isolation to prevent applying power to the VBUS when the IC is in boost mode. This can be omitted since it appears you are not using OTG boost function. 

    -For OTG pin circuit feel free to connect to ground via 10Kohm resistor so OTG is disabled. Please be aware that in buck mode if a USB host input is detected via D+/D- lines OTG pin driven low will set the initial input current to 100mA. This input current limit setting can be overridden via I2C setting. For more information on D+/D- detection and setting the input current limit please refer to pages 13 and 14 in the BQ24195L datasheet. 

    Let me know if you have any additional questions.

    Best Regards,

    Garrett