BQ24075T: Transient response issue

Kai Hsiao

Part Number: BQ24075T

Hi Sir

This issue will happen when the battery exist only without adapter

When the OUT pin have suddenly current transient from 1A to 3.5A ,Vout-Vbat will bigger than 250mV and the charger will turn-off the OUT

I saw the continue current support 5A on BQ24075T

May I know the current transient limitation of BQ24075T? or have any idea how to solve this issue ?

Thanks

Below

Pink = VBAT

Yellow = OUT

Green = Battery output current

over 6 years ago

0 Raheem over 6 years ago

TI__Mastermind 21590 points

Hello Kai,
This is due to the output short circuit protection. You can add a FET between BAT and OUT in parallel to the BATFET internal to the device.

0 Kai Hsiao over 6 years ago in reply to Raheem

Guru 12675 points

HI Raheem

1. Does TI have internal test report for this issue ,We would like to know what's the condition will not have this issue ,for example current slope under 1A/uS ?
2. About the parallel FET ,could you provide the reference design to me ?
3. PMOS or NMOS

0 Raheem over 6 years ago in reply to Kai Hsiao

TI__Mastermind 21590 points

Hello Kai,
I don't currently have a test report for this. However, it'll relate to the RDSON of the BATFET and the load at that point. That will cause the voltage drop from the BATFET to OUT. You can connect an external PMOS between VBAT and OUT with the gate of the PMOS connected to VIN.

0 Kai Hsiao over 6 years ago in reply to Raheem

Guru 12675 points

Hi Raheem

May I know the Rds(on) maximum value ?

Thanks

0 Raheem over 6 years ago in reply to Kai Hsiao

TI__Mastermind 21590 points

Kai,
The maximum BATFET RDSON is 100mohms.

0 Kai Hsiao over 6 years ago in reply to Raheem

Guru 12675 points

Hi Raheem

I have a little confuse ,if the Rds(on) of Q2 is 100mhom
How could BQ24075T work 4.5A discharge ?

Thanks

0 Raheem over 6 years ago in reply to Kai Hsiao

TI__Mastermind 21590 points

Hello Kai,

The maximum RDSON is 100mohms. The typical value is 50mohms.

We enter output short protection when VOUT < VBAT by 250mV (typ). This number also varies with a minimum of 200mV and max of 300mV. Our maximum output current in the datasheet is 4.5A.

With 50mΩ we have a drop of (50mΩ * 4.5A) which is ~225mV which is below our typical value for the short circuit detection threshold.

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BQ24075T: Transient response issue