BQ25302: ICHG level setting, handling low battery condition

Genius 17165 points

Part Number: BQ25302

Hi all

My customer has a design with the BQ25302 and has three current limits selectable by the uC I/Os (schematic below).

100mA / 500mA / 1A

What happens in a low battery situation when the uC is not running ?

Consulting the datasheet I assume the BQ25302 will not charge / switch.

How should one handle this situation ?

.... just have the R112 (420k) connected to GND so that by default the BQ25302 will start with 100mA ?

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The customer has a second question for page 9 of the datasheet:

RICHG_HIGH ICHG setting resistor threshold to clamp precharge and termination current to 63mA RICHG > RICHG_HIGH 60.0 65.0 70.0 kΩ

He is not sure what this means, can you elaborate ?

Thank you for providing feedback.

Best regards

Ueli

over 4 years ago

0 Kedar Manishankar over 4 years ago

TI__Mastermind 24075 points

Hi,

During low battery condition (VBAT_SHORT) charger will charge at IBAT_SHORT = 30mA. When VBAT_SHORT<VBAT<VBAT_LOWV charger will charge at precharge current which is 10% of ICHG. If charge current is set to <630mA, the precharge and termination current will be clamped to 63mA.

0 Ue over 4 years ago

TI__Genius 17165 points

Hi Kedar

Thank you for the quick reply. To clarify:

Does this mean the customer can leave his schematic as is and it will work ok ?

The customer is somewhat confused as this contradicts what is stated on page 4 of the datasheet:

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When ICHG pin is pulled to ground or left open, the charger stop switching and STAT pin starts blinking.

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Can you clarify ?

Best regards

Ueli

0 Kedar Manishankar over 4 years ago in reply to Ue

TI__Mastermind 24075 points

Hi Ueli,

If ICHG is shorted to GND it will be a fault. If it is pulled to GND through a resistor, then a charge current will be set according to the equation given in the datasheet. When MCU is disabled, will the GPIO pin pull ICHG pin to GND? If GPIO is left floating, then you will have an ICHG fault as ICHG pin would be open.

0 Ue over 4 years ago in reply to Kedar Manishankar

TI__Genius 17165 points

Hi Kedar

As configured today it would be floating, the MCU would no longer work in a low battery condition.

Therefore the MCU couldn't pull down the I/Os.

Best regards

Ueli

+1 Kedar Manishankar over 4 years ago in reply to Ue

TI__Mastermind 24075 points

Hi Ueli,

Then it would be a fault condition.

+1 Ue over 4 years ago in reply to Kedar Manishankar

TI__Genius 17165 points

Hi Kedar

Thank you for the clarification.

I will then inform the customer that he has to use one fixed resistor to GND to prevent this .

Best regards

Ueli

Power management

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BQ25302: ICHG level setting, handling low battery condition