BQ77905: Doubts regarding BQ7790518

Goutam Ghosh

Prodigy 100 points

Part Number: BQ77905
Other Parts Discussed in Thread: BQ7718

Tool/software:

Hi,

I am planning to use BQ7790518 battery protector for 8 and 6 Cells. The following specs are required:

1. The cell level overvoltage cutoff at 4.3V.

2. The temperature cut off can be 150 deg C at board level.

3. This circuit will not be used during discharging, only charge OV protections are required.

Can I short the SRP and SRN pins?

over 1 year ago

0 Max Verboncoeur over 1 year ago

TI__Mastermind 25980 points

Hi Goutam,

You can short SRP and SRN, although this will affect the body diode protections and the state comparator described in Section 8.3.6. One thing to note is that the device is only recommended for up to 85 deg C.

If you're only looking for an OV protector, then you may also want to look into stacking 2x BQ7718.

Regards,

Max Verboncoeur

0 Goutam Ghosh over 1 year ago in reply to Max Verboncoeur

Prodigy 100 points

Thank you Maxwell for your response. I will surely look into your suggestion of BQ7718. In my case the ambient temperature will be maximum 55 deg C will it be a problem for BQ7790518?. Also, please note that the temperature protections I have included in the charger itself and for BQ7790518, I have disabled the temperature protection by fixing the voltage across the TS PIN to be 50%VTB always. Will it work fine?

0 Goutam Ghosh over 1 year ago in reply to Goutam Ghosh

Prodigy 100 points

Can you please verify the schematic?

0 Goutam Ghosh over 1 year ago in reply to Goutam Ghosh

Prodigy 100 points

I am also looking into BQ7718 design considerations.

0 Max Verboncoeur over 1 year ago in reply to Goutam Ghosh

TI__Mastermind 25980 points

Hi Goutam,

Goutam Ghosh said:
In my case the ambient temperature will be maximum 55 deg C will it be a problem for BQ7790518?

55 deg C is not an issue, this is within the recommended limits.

Goutam Ghosh said:
Also, please note that the temperature protections I have included in the charger itself and for BQ7790518, I have disabled the temperature protection by fixing the voltage across the TS PIN to be 50%VTB always. Will it work fine?

Using a fixed 10k resistor is the recommended method for disabling the temperature protections on this device, so this will work as expected.

Regards,

Max Verboncoeur

0 Goutam Ghosh over 1 year ago in reply to Max Verboncoeur

Prodigy 100 points

Thank you very much for your response. Can you please check the schematics? Again, the requirements remain same, the overvoltage cut-off should trigger at 4.3V per cell. Also, I have kept the sensing resistor for accurate current sensing as well as safe turn ON of the CHG and DSG MOSFETs. Note that, this circuit will not be used for discharging. Hope the schematic is correct and good to go.

0 Max Verboncoeur over 1 year ago in reply to Goutam Ghosh

TI__Mastermind 25980 points

Hi Goutam,

The schematic looks good, the only thing out of place is the TS connection on the top device. R17 should go to the local device ground, not all the way to BAT-.

Regards,

Max Verboncoeur

0 Goutam Ghosh over 1 year ago in reply to Max Verboncoeur

Prodigy 100 points

Thats correct. Thank you for pointing that out.

Thanks once again for your assistance.

Regards

Goutam

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BQ77905: Doubts regarding BQ7790518