iMX28 Battery charger

[victorien]

Hi,

I'm working on iMX28 the battery charger module and I miss some informations :

- What is the minimum supply voltage for the 5V ?

- What is the linear dropout of the linear regulator inside the charger ?

- When I set the charge current at 200mA, I measure 210mA. Is it normal ?

- What is the precision of the current regulator ?

I made a test with a full charge of a battery and the result is strange (cf picture MesureCharge20140327.png).

When the battery voltage is greater than 3.9V, the charge current decrease and it's not normal.

Is there someone who already works on the imx28 charger ?

[gusarambula]

The charge vs voltage graph looks generally fine as current must drop to zero by the time the battery is fully charged. Please look at Figure 12 of the Using the i.MX28 PMU Application Note (AP4199, link below) to see the curves for voltage and current while charging.

http://cache.freescale.com/files/32bit/doc/app_note/AN4199.pdf

There is information on this Application Note that might be of help. As for the minimum supply voltage for VDD5V, it would be 4.75V and a max of 5.25V as shown in Table 8 of the I.MX28 Datasheet (link below). The accuracy for the regulators is also listed on this document in Table 13.

http://cache.freescale.com/files/32bit/doc/data_sheet/IMX28CEC.pdf

[victorien]

Thanks for your answer.

I read Application Note AP4199 before doing my test and for a normal charge, the current is stable until the voltage is 4.2V. On my test (first message), it wasn't correct.

I continued my test with the charger driver writing for linux and it's look better (but not perfect) ; see picture below

I check the difference on the configuration and its's the parameter DROPOUT_CTRL on register HW_POWER_DCDC4P2. if the brownout is 25mV (1st measure) it's bad and if it's 100mV (2nd measure) it's better.

Can you explain me how this parameter change the charge current ?

Normally, the current when the voltage is between 3V and 4.2V but I don't have this result with imx28 (with another battery charger it works) : the current isn't stable and not at the specified current (0.4A). Can you explain that ?

[gusarambula]

Would you please share the complete value for the DROPOUT_CTRL bits on register HW_POWER_DCDC4P2 for the first and second graphics?

[victorien]

For the first one, DROPOUT_CTRL = 0x2 (Brownout below the target = 25mV, DCDC select DCDC_4P2 or battery) ; HW_POWER_DCDC4P2 = 0x20c0001f

For the second one, DROPOUT_CTRL = 0x8 (Brownout below the target = 100mV, DCDC powered by DCDC_4P2 only) ; HW_POWER_DCDC4P2 = 0x80c0001f

[gusarambula]

I would say the change on the curve is most likely related to the change of the power source selected by the DCDC converter after ENABLE_DCDC is set.

On the first one DCDC uses VPDD4P2 or BATTERY depending on which is higher. This switch affects the curve.

On the second one DCDC is always using DCDC_4P2 regardless of BATTERY voltage, thus the curve would be smoother.

[victorien]

Thanks.

For the second test, the curve is smoother. it's better but with a good LiIon charger, the "constant current" period is flat (in the past, I did test with some chargers like TI BQ24032A, see picture).

Then, I think there is a problem with the imx28 charger but I need information from Freescale to understand it

[YixingKong]

Victor

This discussion is closed since no activity. If you still need help, please feel free to reply with an update to this discussion, or create another discussion.

Thanks,

Yixing

[YixingKong]

Victor

We have not got your response yet and will close the discussion in 3 days. If you still need help, please feel free to reply with an update to this discussion.

Thanks,

Yixing

[YixingKong]

Victor

Had your issue got resolved? If yes, we are going to close the discussion in 3 days. If you still need help, please feel free to reply with an update to this discussion.

Thanks,

Yixing