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BQ76200: BQ76200, Inrush current protecting

Dongwoo Shin
Prodigy 20 points
Part Number: BQ76200
Other Parts Discussed in Thread: BQ78350, , BQ76930, LM5069, LM5060

Hello

We are developing a battery pack for e-bikes.
Our problem is inrush current.

The ic we use is as follows.
We developed the product using BQ76930 + BQ78350 + BQ76200.

Our FET circuit diagram is as follows.

https://drive.google.com/file/d/1OECMG2Z0VyjeFhBfp6cE12HQRdz6l6iY/view?usp=sharing

Secondary battery lithium-ion battery pack: 42V

Operating voltage: 30V ~ 42V

Discharge maximum current: 120A

Charging maximum current: 19A

The charge/discharge connector uses a single connector (charge connector = discharge connector).

The charging FET and the discharging FET are connected in series (the charging/discharging fet is turned on at the same time).

The circuit is made of N-channel High-side.

When the battery pack is connected to the charger, the charging/discharging fet is turned on first,
Then, as the charger's relay is attached, an inrush current is generated as shown in the figure below.

Time: about 40ms
Current: 40A max
Voltage: 50V max
The occurrence is set up and down as above.

Is there any good solution to this?

Since the charging/discharging connector is the same, it must flow normally even if it flows over 120A during discharge,

and the inrush current that occurs when the relay is attached or when the fet is turned on must be prevented.

If you have a good idea, please advise.

Thank you.

  • 0
    TI__Guru 54715 points

    Hi Dongwoo,

    The BQ76200 does not know what current will be flowing and can not control the current flow other than to open the switch on command.  It does not monitor current but responds to control from the BQ76930 or BQ78350.  In a battery current is commonly limited at turn on by a pre-charge or pre-discharge circuit, these are only operable in certain modes of operation, once the battery is on it is allowed to flow full current up to its limit.  The BQ78350 can set an OCC threshold, but it will respond slowly with the average current from the CC of the BQ76930.  If you need a faster response it will take a separate circuit.

    It seems you want a current limiter in the charge path, or since there is one set of terminals, in the current path to limit charge current. Inrush current limiters are common in electronic circuits, you may have seen the application note https://www.ti.com/lit/an/slva670a/slva670a.pdf.  At TI most current limiting is included with efuses and hot swap controllers, see www.ti.com/hotswap for devices. Some designers will include additional switching devices in their current path.  You might look at products such as the LM5060 or LM5069, but check the features of the device and look for operating limits and currents which may be undesired in a battery. If you select a device their experts will know that product better and offer guidance if needed.