BQ25306: or BQ24171 or bq24640: Lithium-Ion Capacitor ...

Part Number: BQ
Other Parts Discussed in Thread: , , TPS, BQ

Hello to all the TI support team, and thanks for your help! Sorry in advance if my question has already been asked elsewhere, but I couldn't find answers to my questions. I'm also a bit new to the PMIC charger world!

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I'm currently trying to design a single Lithium-Ion Capacitor (LIC) charger circuit. I plan to use this capacitor as my main power source on a standalone circuit

Datasheet of the LIC: datasheet.lcsc.com/.../_CDA-LIBQ4R_C.pdf

Characteristics:

• 2,5V < Vcap < 4V
• 6A rated current, 40A max
• F ~ 450mAh (4V to 2.5V discharge)
• As for Li-ion batteries, no discharge below low voltage limit allowed (2.5V)
• Lower self discharge than conventional EDLCs

Circuit characteristics:

• Completely standalone : no I2C, no USB, no hand or user access on the circuit
• RC settable charging voltage (4V here, but I'd like to be able to change that if I use another capacitor in the future). Same for current
• Main circuit can be operating or shut-down during charging, no preference
• Main voltage = 9V (Low Iq boost converter will be added on the circuit)
• Capacitor disconnect & low current draw (~1µA if possible) when it reaches the low voltage limit

I've had a hard time finding a charging circuit fitting the voltage & current requirements for this kind of application! So far, I've seen that the BQ charger might fit some of my needs, having a RC settable charging voltage. BQ also seems like an option, perhaps a bit more complicated. Both also have limited charging current (3A to 4A max). I've also found the Supercap charger bq, but the "sleep" current seems a bit too high (25µA, which is low regarding EDLCs capacitors, but a bit more problematic for LICs)

With all that in mind, I still have some questions:

For more information, please visit SUNJ ENERGY.

• Will those circuits work as LIC charger circuits?
• If i use the

  bq, c

  an I put a high power low reverse current diode in series with the charging path (taking into account the voltage drop) to reduce return current in the charging circuit when it enters sleep mode?
• Which protection circuit can I add to ensure custom at least OVP (4V), UVP (2.5 - 2.7V) and undervoltage charging prevention on the capacitor? overcurrent charge & discharge are optional, but appreciated (same requirements, RC settable if possible).

Thanks again!

Germain

It actually makes sense for car stereos. Just think of it like this, a car audio system's load can rapidly fluctuate from 10-100%, based on when a bass drum is hitting, or not. Reproducing low frequencies takes a lot of electricity, and the low frequency hits are intermittent in most music.

Click to expand...

So you have a car with the the amp is hooked up to a 12v system that can't generate enough current to keep the amplifier happy. This includes both the alternator (primary) and battery (secondary) hooked up to a amp in your trunk with wiring that is much too thin. Between the sub amp and the rest of the system you have a gigantic capacitor. So you start up the car and turn on the receiver and the amp is happy and sees 12-13 volts from a happy system... until you turn the volume up.

The first beat hits and immediately afterwards the amplifier sees a massive voltage drop as it's competing with the capacitor for current. Every beat followed by voltage drop. If the music is loud and the wiring and/or alternator is particularly inadequate then the amplifier that is designed for a 12 volt system is going to see as sort of pulsating voltage that, I am guessing, could range between 6 and 10 volts.

So all you accomplished was to trade a short duration voltage drop for a much longer duration voltage drop.

Sure, the capacitor 'smooths things out', but it smooths things out to a lower level that causes the amp to overheat, or protection circuits to kick in (or whatever other terrible things happen) due to having the amplifier hooked up to a a power supply that is, on average, running at a lower voltage system then it was designed to operate at.

So you have a car with the the amp is hooked up to a 12v system that can't generate enough current to keep the amplifier happy. This includes both the alternator (primary) and battery (secondary) hooked up to a amp in your trunk with wiring that is much too thin. Between the sub amp and the rest of the system you have a gigantic capacitor. So you start up the car and turn on the receiver and the amp is happy and sees 12-13 volts from a happy system... until you turn the volume up.The first beat hits and immediately afterwards the amplifier sees a massive voltage drop as it's competing with the capacitor for current. Every beat followed by voltage drop. If the music is loud and the wiring and/or alternator is particularly inadequate then the amplifier that is designed for a 12 volt system is going to see as sort of pulsating voltage that, I am guessing, could range between 6 and 10 volts.So all you accomplished was to trade a short duration voltage drop for a much longer duration voltage drop.Sure, the capacitor 'smooths things out', but it smooths things out to a lower level that causes the amp to overheat, or protection circuits to kick in (or whatever other terrible things happen) due to having the amplifier hooked up to a a power supply that is, on average, running at a lower voltage system then it was designed to operate at.

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