Date:   Tue, 14 Mar 2017 14:44:21 +0100
From:   Quentin Schulz <quentin.schulz@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        devicetree <devicetree@...r.kernel.org>,
        Liam Breck <liam@...workimprov.net>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-iio@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Icenowy Zheng <icenowy@...c.xyz>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>, knaack.h@....de,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Bruno Prémont <bonbons@...ux-vserver.org>,
        Lee Jones <lee.jones@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 01/18] dt-bindings: power: battery: add
 constant-charge-current property

Hi Chen-Yu,

Sorry for the late reply.

On 21/02/2017 05:55, Chen-Yu Tsai wrote:
> On Wed, Feb 15, 2017 at 4:53 PM, Quentin Schulz
> <quentin.schulz@...e-electrons.com> wrote:
>> Hi,
>>
>> On 15/02/2017 01:46, Liam Breck wrote:
>>>
>>> On Tue, 14 Feb 2017 10:40:55 +0100 Quentin Schulz wrote:
>>>> This adds the constant-charge-current property to the list of optional
>>>> properties of the battery.
>>>>
>>>> The constant charge current is critical for batteries as they can't
>>>> handle all charge currents.
>>>>
>>>> Signed-off-by: Quentin Schulz <quentin.schulz@...e-electrons.com>
>>>> ---
>>>>
>>>> added in v3
>>>>
>>>>  Documentation/devicetree/bindings/power/supply/battery.txt | 2 ++
>>>
>>> Is constant-charge-current dependent on the battery (e.g. capacity, nominal voltage, etc) or the
>>> system (charger chip, input current/voltage, etc)?
>>>
>>> It belongs in Doc.../power/supply/battery.txt if it's a characteristic of the battery.
>>>
>>> Note, this page asserts that constant-current charging applies to NiMH batteries:
>>> http://power-topics.blogspot.com/2016/05/constant-voltage-constant-current.html
>>>
>>> Related properties to be added to battery.txt near-future in a patchset for the BQ24190
>>> charger are as follows. These are not currently in enum power_supply_property, so the actual names
>>> are still to be decided.
>>>
>>> precharge-current-microamp:
>>>    maximum charge current during precharge phase (typically 20% of battery capacity)
>>>
>>> termination-current-microamp (or endcharge-current):
>>>    a charge cycle terminates when the battery voltage is above recharge threshold,
>>>    and the current is below this setting (typically 10% of battery capacity)
>>>
>>
>> We have a client with a board whose battery accepts a maximum of 300mA
>> for charging. So depending on the battery, we cannot have any charging
>> current we want. The AXP PmMICs set constant charge current in a range
>> of 300mA-1800mA, so it is enforced by the charger but needs to be
>> adapted depending on the battery present in the system.
> 
> May I ask the capacity of the battery in question?
> 

It is a 400mAh battery.

Quentin

> Typically one charges LiPo batteries at no more than 1C. So if it's
> a 1800 mAh battery, the charge current should be no more than 1800 mA.
> 
> ChenYu
> 
>> The AXP PMICs charge battery with constant current (Ichrg) between the
>> trickle voltage (Vtrkl which is ~3.0V) and the targeted voltage (Vtrgt;
>> which seems to be the voltage telling the battery is fully charged).
>>
>> So if I understand correctly, "my" constant-charge-current would be
>> located in the charging cycle between your precharge-current-microamp
>> and the termination-current-microamp as it is the current for the
>> charging process as a whole.
>>
>> See here[1] for the explanation in the datasheet (page 20).
>>
>> That would definitely match what is explained in your link for constant
>> current.
>>
>> [1] http://dl.linux-sunxi.org/AXP/AXP209_Datasheet_v1.0en.pdf
>>
>> Let me know if something seems odd,
>> Thanks,
>> Quentin
>>
>> --
>> Quentin Schulz, Free Electrons
>> Embedded Linux and Kernel engineering
>> http://free-electrons.com
> 
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> 

-- 
Quentin Schulz, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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