BQ24773: Don't charge

meifu ding

Prodigy 10 points

Part Number: BQ24773

Hi,

There is a charging issue by using BQ24773.

Our product uses 36Ah battery. (18P2S - 8.4V Li battery)

Use 12V/5A adapter to charge. We plan this charger can reach to 5A current for battery.

But it can't charge completely. Attached is our circuit design.

Below is the register configuration.

* When battery is not installed, it can read the register shows it is invalid charging. But the charge voltage is correct.

The power rail of the battery connector is 8.4V. And system voltage is also 8.4V.

ChargeVol_L=00
ChargeVol_H=21
Current5A
ChargeCurrent_L=80
ChargeCurrent_H=13
MAX_CHARGE_VOLTAGE_L=00
MAX_CHARGE_VOLTAGE_H=20
CHARGE_CURRENT_L=18
CHARGE_CURRENT_H=50

* When battery is installed, it will not charge. The voltage reduces to 7.6V. (It is equal to battery voltage) And the system voltage is also 7.6V.

It looks the adapter stops charging & supply and uses the battery discharge instead to the system.

It is abnormal.

ChargeVol_L=00
ChargeVol_H=21
Current5A
ChargeCurrent_L=80
ChargeCurrent_H=13
MAX_CHARGE_VOLTAGE_L=00
MAX_CHARGE_VOLTAGE_H=21
CHARGE_CURRENT_L=00
CHARGE_CURRENT_H=00

Please help clarify this issue.

Thanks!

Circuit Design.pdf

over 3 years ago

0 meifu ding over 3 years ago

Prodigy 10 points

Please help review the circuit design whether it is right at first. Then share the right register configuration with us. Thanks!

0 Kedar Manishankar over 3 years ago in reply to meifu ding

TI__Mastermind 24075 points

Hi,

The EVM user guide is a good resource to use to verify your schematic against: www.ti.com/.../sluua74.pdf

0 meifu ding over 3 years ago in reply to Kedar Manishankar

Prodigy 10 points

Hi Kedar,

Thanks for your feedback.

But your recommended schematic is not the right EVM user guide for BQ24773.

Let me share the right EVM with you. We refer to this user guide to design.

But it appears above issues.

Let me supplement another issue.

That is, there is 7.6V abnormal voltage in the battery connector terminal when battery is not present. (The BATDRV is high(9V))

Please help clarify these two issues.

Thanks!

BQ2477x User Guide.pdf

0 Kedar Manishankar over 3 years ago in reply to meifu ding

TI__Mastermind 24075 points

Hi,

Can you take waveform capture of VBAT, when battery is absent?

0 meifu ding over 3 years ago in reply to Kedar Manishankar

Prodigy 10 points

Hi Kedar,

Please refer to below waveform for VBAT without battery. Thanks!

0 Kedar Manishankar over 3 years ago in reply to meifu ding

TI__Mastermind 24075 points

Hi,

With battery absent, charger IC only sees the small output capacitance on VBAT. It will charge the output cap quickly due to its relatively small capacitance, and because of the small capacitance, capacitor will discharge quickly after charge as well. You will observe this expected charge/discharge of the output capacitor when battery is absent.

0 meifu ding over 3 years ago in reply to Kedar Manishankar

Prodigy 10 points

Hi Kedar,

In my opinion, BATDRV is not enabled so that VBAT should not have any voltage because of P-MOS no conduction with battery absent. Even though VBAT has a small output capacitance, it may not be in charge and discharge mode. Please refer to schematic to help review it. Thanks!

0 Kedar Manishankar over 3 years ago in reply to meifu ding

TI__Mastermind 24075 points

Hi,

This is not how BATDRV works. BATDRV will be off to prevent BAT form being connected to SYS. But BAT is still being charged through the PHASE node.

BATDRV only dictates whether or not SYS is powered by adapter or battery.

Power management

Power management forum

BQ24773: Don't charge