BQ24040: Placement for Lithium charger circuit

Karthik Menon1

Part Number: BQ24040

Hi,

We are building a Lithium polymer powered product. The product will have a separate charger housing which will charge the former when mounted on it. Since space inside the product is a constraint, is it fine if I place the Lithium charging circuit inside the charger housing and produce the 'OUT' pin and 'VSS' pin as the charging terminals? On the product side a low-drop diode can be placed to prevent risk of the terminals shorting.

Is this recommended? If not, kindly let me know why.

Thanks!

over 5 years ago

0 Bill Johns over 5 years ago

TI__Guru* 75656 points

Hello

Separating the charger and battery would be possible. There are some risks.

How large a charge current are you planning on using?

The diode should not be in series with the charge path, voltage drop will cause problems.

0 Karthik Menon1 over 5 years ago in reply to Bill Johns

Prodigy 50 points

Hi Bill,

The maximum charging current will be 15 mA.

Can you suggest any other way to protect the battery in case the charging terminals on the product housing get accidentally shorted?

0 Karthik Menon1 over 5 years ago in reply to Bill Johns

Prodigy 50 points

Also, what if I use some ideal diode that gives a voltage drop of only less than 50mV?

0 Bill Johns over 5 years ago in reply to Karthik Menon1

TI__Guru* 75656 points

Hello

"What if I use some ideal diode that gives a voltage drop of only less than 50mV" -- Reducing the voltage drop would help, improve charge accuracy. The battery detection circuit may cause problems due to diode, the detection routine will supply current the sink current. May not be able to sink current with the diode.

Also some other connections to consider:

For TS function would need dedicated connection -- This is a temp monitor of the battery during charging, needs to be with battery.
\chg and \pg (if used) would need dedicated connection -- Two status pins out of the charger often connected to LEDs or micro contorler.

0 Karthik Menon1 over 5 years ago in reply to Bill Johns

Prodigy 50 points

Thank you for the help! That helps!

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BQ24040: Placement for Lithium charger circuit