BQ24072: Charging current too low

Tandeep Chadha

Part Number: BQ24072

Hi,

I have a bq24072 connected as follows:

EN2: 1 and EN1:0 (not as shown in the diagram) so current limit should be determined by ILIM.

When i connect an external 2.1A max external USB charger, the ~CHG LED goes ON but the battery does not charge. I measured the voltage across ISET and it is only 0.4mV which translates to a charging current of 0.14mA. Although the calculated charging current for this circuit should be 800mA. The VSUP is not consuming more than 600mA of current when the load is running and <5mA when the load is not running.

Can you suggest why the charging current is so low?

over 6 years ago

0 Raheem over 6 years ago

TI__Mastermind 21590 points

Hello Tandeep,
Some of the resistor values are hard to see. How many ohms do you have on ILIM?

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

Resistor values are as follows:
ILIM: 1.18k
ISET: 1.13k
TS: 10k
TMR: unconnected

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Tandeep,
Does the device charge when there is no load on OUT?

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

No it does not. If there is no load to out, the PGOOD and the CHG LED also do not turn on.
The output to VBATT when no load on OUT is 3.78V which is the battery voltage.

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

What is the voltage on OUT wen this happens?

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

When no load is connected and battery also not present Vout is 4.37V.
When no load is connected and battery present, Vout is 4.10V
In either of the above case, the CHG and PGOOD LED are not ON.

If load is connected, the CHG and PGOOD LED turn ON. Vout with battery present is 4.10V, without battery it is 4.37V

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Tandeep,
That doesn't sound correct. When the battery isn't present on the BQ24072, VOUT should be 3.4V. Can you tell me what the markings on the IC are? Also check for shorts on the IN, BAT and OUT pins and let me know what the input current is when this issue occurs.

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

When battery isn't present, VOUT is 4.31V. When i place a fully charged battery (charged using external charger), the CHG LED is OFF as expected. The markings on the IC are: PAP TI 74 Z64W. I have checked for shorts on the IN, BAT and OUT pins and none exist.

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

My main issue is the battery not charging which is happening no matter what the load is. The input current when load is ON is 160-220 mA.

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Tandeep,
Can you check the voltage on the TS pin when the charger doesn't charge.

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

TS pin reads 0V whether the battery is connected or not. The charger is never charging.

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Tandeep,
The TS pin needs to be within the appropriate threshold of 0.3V and 2.1V for charging. Please place a 10K ohm resistor on the TS pin and check again if you don't intend to use the TS feature.

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

I already have a 10K ohm resistor from TS to GND as shown in the schematic

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Can you connect a 0.5V on the TS pin using a source meter and check if the battery starts to charge.

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

If i connect 0.5V externally to TS, the VBATT is now 4.11V. That suggests that the battery is charging now. VOUT to the circuit under the load is still 4.34V.
Effective resistance across at the TS pin is 5kohm. Is TS internally pulled down as well?

0 Tandeep Chadha over 6 years ago in reply to Tandeep Chadha

Prodigy 110 points

Sorry, i was using a charged battery which already was supplying 4.11V for the above reply.
Correction: If i connect 0.5V externally to TS, the VBATT is now 3.95V. So i don't think the battery is still charging. If TS is 0V then the VBAT is 3.78V (battery voltage)

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

What is the current into the battery when 0.5V is connected to TS? Does the input current increase?

0 Tandeep Chadha over 6 years ago in reply to Raheem

Prodigy 110 points

When 0.7V is connected to the TS, the current to battery increases to 400mA without any load and battery volt is 3.99V and 570 mA with the load. That suggests that the battery is charging. If i remove the 0.7V bias (10K resistor to ground is still connected) the input current drops to 0 under no load and 170-200mA under load (from my circuit).
I am unable to understand why the TS is not functioning normally with the 10K resistor to GND on it.

0 Raheem over 6 years ago in reply to Tandeep Chadha

TI__Mastermind 21590 points

Tandeep,

Based on your device marking, it seems you have the BQ24072T which has a voltage based TS functionality and not the BQ24072 which has a current based TS. That is the reason why the TS function is not functioning as expected. Please take a look at the BQ24072T datasheet on how to configure the BQ24072T TS pin.

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BQ24072: Charging current too low