topic MX23 Battery Charger Current Limit in i.MX Processors

MX23 Battery Charger Current Limit

RobertSchwebel — Thu, 19 Sep 2013 10:31:04 GMT

We are trying to get the charging unit on i.MX23 SoC to work. Principally it does its job.

The i.MX23 limits its current consumption to about 400 mA .. 500 mA from the 5V input, while the setting in the "CHARGE_4P2_ILIMIT=0x3ff" is 780 mA. The charging current for the LiPo battery "BATTCHRG_I=0x300" is set to 600 mA, but the battery does not draw this current (it only draws about 300 mA; this value is all right, because the battery is almost full).

Problem is, when the system load increases (for example playing a movie with 100 % CPU load), not the overall SoC input current increases, the battery charge current decreases instead (without changing the register settings). Note: at this point of time the temperature monitor still reports sane SoC temperatures.

Is there a know limit for the input current? I did not find any hint in the "Chip Errata for the IMX23" document.

rsc+jbe

Re: MX23 Battery Charger Current Limit

arthur_lai — Mon, 23 Sep 2013 07:07:35 GMT

The 5V input is used as the supply for the battery battery and as system supply as the same time (5V is regulated to 4.2V on VDD4P2 to power the on-chip DCDC).

The total current from 5V is controlled by CHARGE_4P2_ILIMIT. So, the CHARGE_4P2_ILIMIT controls total current taken by the battery charger and the system. In addition, in order to ensure the i.MX233 running properly, the PMU has a feature that provide higher priority to the VDD4P2. Current on the battery charger will be reduced when total current consumed on VDD4P2 and battery charger exceed the current set by CHARGE_4P2_ILIMIT. So, your observation is expected.

For more detail, please refer to Figure 32-1, section 32.6, and register description of CHARGE_4P2_ILIMIT bist on the reference manual.

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Tue, 24 Sep 2013 07:06:41 GMT

Hi Arthur,

Please re-read my original posting. Our understanding is that setting CHARGE_4P2_ILIMIT=0x3ff should limit the total (CPU+Charger) current to 780 mA.

In fact, we are only observing 500 mA total current on the 5 V supply rail.

Regards,

Robert

Re: MX23 Battery Charger Current Limit

Tarek — Tue, 24 Sep 2013 08:15:44 GMT

I'm not expert in this area, but 500 mA is the current limits when charging from USB. "ie. connecting the device to a PC using USB".

Is there any configuration option to tell the device that this is not USB charging but an external charger?

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Tue, 24 Sep 2013 09:04:26 GMT

Tarek,

In general this is true for USB, but according to the documentation, the MX23 should be able to draw up to 780 mA. The hardware in question has an USB port and a charger connector, and it is possible to detect if the 5 V comes from the USB port or from the charger. When running on the charger, we would like to charge as fast as possible, of course.

rsc

Re: MX23 Battery Charger Current Limit

karina_valencia — Tue, 24 Sep 2013 20:38:24 GMT

arthur_lai can you continue with the follow up on this case?

Re: MX23 Battery Charger Current Limit

arthur_lai — Wed, 25 Sep 2013 02:37:52 GMT

Hi Robert,

Are you using a power supply or connecting the board to a USB host when you are seeing a 500mA current on VDD5V?

In addition, can you dump to registers for the PMU to confirm the settings is what you expected?

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Wed, 25 Sep 2013 14:02:44 GMT

Tarek,

It would indeed be interesting if there was a bit which needs to be set if we are on an external power supply and not on USB.

However, we didn't find such a bit yet, and the original FSL drivers do not contain it as well (so the current is also limited there).

rsc

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Wed, 25 Sep 2013 14:11:14 GMT

Hi Arthur,

We are using a power supply in that case; in fact, the MX23 does only have one pin for 5 V.

The original FSL power driver does directly call into the USB core in order to find out if there is an USB devices connected, without taking care of any abstraction or locking. For testing purposes, we currently fake this call to tell the power code to be always connected to a power supply and not to an USB device.

We have dumped the registers; even when setting both to 0x3ff (maximum value), the behaviour isn't different.

Another interesting observation: When we increase the system load, the charging current decreases, and also the current on the main supply decreases as well. This can be triggered by switching on some LEDs on our board. With each LED, the current decreases a bit (we expected that it would increase instead). When being idle, we see about 500 mA on the 5 V rail, and when being busy it drops down to 460 mA. We have no idea why it goes down.

rsc

Re: MX23 Battery Charger Current Limit

arthur_lai — Fri, 27 Sep 2013 10:34:49 GMT

Hi Robert,

Just want to confirm that you are using our BSP and is using DCDC with VDD4P2 as input, not using LDOs and the system supply.

And, how much is the charge current drop when you see the system current goes down to 460mA?

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Fri, 27 Sep 2013 12:12:24 GMT

Arthur,

We are using the mainline kernel, not the FSL BSP. In addition, we use the original FSL bootlets (unmodified) and the charging driver (ported to 3.11).

We in fact are using the DCDC converter (at least the bootlets output a corresponding message). But thans for the hint, we will check the bits again.

When the system current goes down, the charge current drops down to about 60 mA (depending on the state of the battery).

Robert

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Tue, 01 Oct 2013 19:51:17 GMT

Any further idea?

rsc

Re: MX23 Battery Charger Current Limit

karina_valencia — Tue, 01 Oct 2013 20:21:39 GMT

HI Robert,

Due Holidays in China, arthur_lai is out this week. He can continue with the follow up next week.

Re: MX23 Battery Charger Current Limit

arthur_lai — Wed, 02 Oct 2013 04:26:29 GMT

Hi Robert,

Can you check the HW_POWER_DCDC4P2 register? There are settings which governs behaviour of the PMU on DCDC4P2 and DCDC_BATT.

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Wed, 02 Oct 2013 09:39:58 GMT

Hi Arthur,

On Tue, Oct 01, 2013 at 09:27:07PM -0700, Ming On Lai wrote:
> Can you check the HW_POWER_DCDC4P2 register? There are settings which
> governs behaviour of the PMU on DCDC4P2 and DCDC_BATT.

In the HW_POWER_DCDC4P2 register we have:

DROPOUT_CTRL: the FSL battery charger driver sets the
               BF_POWER_DCDC4P2_DROPOUT_CTRL(0xa) which means
               100 mV drop and "DCDC converter selects VDD4P2 or
               battery which ever is higher"

This could explain why an increasing CPU load steals battery charging current,
but not why the PMIC doesn't increase its input current from the main 5V
input.

When setting the current limit in CHARGE_4P2_ILIMIT to 780 mA, I would expect
the current on the main 5 V supply to increase up to this limit and *then* the
PMIC should start to steal battery charge current - right?

Instead I see the opposite:

5V main     CPU load    charger
current                 current

500 mA       idle       270 mA
490 mA       light      200 mA
460 mA       full        60 mA

It seems the 4P2 regulator does not use the remaining 280 mA allowed by the
CHARGE_4P2_ILIMIT.

rsc

Re: MX23 Battery Charger Current Limit

arthur_lai — Thu, 03 Oct 2013 08:08:51 GMT

Hi Robert,

There is no explanation for your observation now. The current on 5V should follow the CHARGE_4P2_ILIMIT setting.

Can you perform a register dump of all the PMU registers on run time for us to double check?

In addition, it may be a good idea to send us the PMU part of the schematics to double check too.

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Thu, 03 Oct 2013 09:07:43 GMT

Hi Arthur,

Ok, will do a register dump on monday (it's national holiday today in .de, so most of the staff isn't here on friday as well).

Thanks,

Robert

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Tue, 08 Oct 2013 09:56:16 GMT

Arthur, here is the register dump.

Light load:

- CPU idle
- all LEDs are off, also LCD backlight (supplied via VDDIO)
- overall current consumption 470 mA
- charging current 360 mA

Heavy load:

- CPU 100 % busy
- all LEDs are on, also the LCD backlight
- overall current consumption 440 mA
- charging current 180 mA

Mapped is the area at the physical address 0x80044000

reg
offset
00000000: 00218541 00218541 00218541 00218541 A.!.A.!.A.!.A.!.
00000010: 0003f003 0003f003 0003f003 0003f003 ................
00000020: 00000040 00000040 00000040 00000040 @...@...@...@...
00000030: 00000530 00000530 00000530 00000530 0...0...0...0...
00000040: 0022071e 0022071e 0022071e 0022071e .."..."..."...".
00000050: 0002270a 0002270a 0002270a 0002270a .'...'...'...'..
00000060: 00002614 00002614 00002614 00002614 .&...&...&...&..
00000070: 0000020c 0000020c 0000020c 0000020c ................
00000080: a0c00018 a0c00018 a0c00018 a0c00018 ................
00000090: 00000000 00000000 00000000 00000000 ................
000000a0: 0000305f 0000305f 0000305f 0000305f _0.._0.._0.._0..
000000b0: 00167021 00167021 00167021 00167021 !p..!p..!p..!p..
000000c0: 21038a2e 21038a2e 21038a2e 21038a2e ...!...!...!...!
000000d0: 00030000 00030000 00030000 00030000 ................
000000e0: 01e5060f 01e5060f 01e5060f 01e5060f ................
000000f0: 00000000 00000000 00000000 00000000 ................
00000100: 00000000 00000000 00000000 00000000 ................
00000110: 0000000e 0000000e 0000000e 0000000e ................
00000120: 00000000 00000000 00000000 00000000 ................
00000130: 03010000 03010000 03010000 03010000 ................

jbe + rsc

Re: MX23 Battery Charger Current Limit

arthur_lai — Wed, 09 Oct 2013 10:26:46 GMT

Hi Robert,

The register dump looks ok.

It seems we have not ask the most basic question. Is VDD4P2 powered up properly? Have you checked the voltage? It requires a special sequence to power up.

Thanks,

Arthur

Re: MX23 Battery Charger Current Limit

RobertSchwebel — Wed, 09 Oct 2013 11:47:41 GMT

Arthur,

> The register dump looks ok.

Yes - it's basically what the Freescale driver (ported to mainline) sets up.

> It seems we have not ask the most basic question. Is VDD4P2 powered up properly?

It is, as you can see in the register dump.

> Have you checked the voltage? It requires a special sequence to power up.

The voltage is ok, and we are using the standard bootlets.

Are you sure that loading the battery with more current has ever worked?

Regards,

Robert