Commit a1c7c1a4 authored by Linus Walleij's avatar Linus Walleij Committed by Sebastian Reichel
Browse files

power: supply: Explain maintenance charging 



In order for everyone to understand clearly why we want to use
maintenance charging for batteries, expand the description with two
diagrams and some text.

Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: default avatarMatti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: default avatarSebastian Reichel <sebastian.reichel@collabora.com>
parent 568035b0

include/linux/power_supply.h

+42 −6
Original line number Diff line number Diff line
@@ -374,9 +374,37 @@ struct power_supply_vbat_ri_table { 
 *   These timers should be chosen to align with the typical discharge curve

 *   for the battery.

 *

 * When the main CC/CV charging is complete the battery can optionally be

 * maintenance charged at the voltages from this table: a table of settings is

 * traversed using a slightly lower current and voltage than what is used for

 * Ordinary CC/CV charging will stop charging when the charge current goes

 * below charge_term_current_ua, and then restart it (if the device is still

 * plugged into the charger) at charge_restart_voltage_uv. This happens in most

 * consumer products because the power usage while connected to a charger is

 * not zero, and devices are not manufactured to draw power directly from the

 * charger: instead they will at all times dissipate the battery a little, like

 * the power used in standby mode. This will over time give a charge graph

 * such as this:

 *

 * Energy

 *  ^      ...        ...      ...      ...      ...      ...      ...

 *  |    .   .       .  .     .  .     .  .     .  .     .  .     .

 *  |  ..     .   ..     .  ..    .  ..    .  ..    .  ..    .  ..

 *  |.          ..        ..       ..       ..       ..       ..

 *  +-------------------------------------------------------------------> t

 *

 * Practically this means that the Li-ions are wandering back and forth in the

 * battery and this causes degeneration of the battery anode and cathode.

 * To prolong the life of the battery, maintenance charging is applied after

 * reaching charge_term_current_ua to hold up the charge in the battery while

 * consuming power, thus lowering the wear on the battery:

 *

 * Energy

 *  ^      .......................................

 *  |    .                                        ......................

 *  |  ..

 *  |.

 *  +-------------------------------------------------------------------> t

 *

 * Maintenance charging uses the voltages from this table: a table of settings

 * is traversed using a slightly lower current and voltage than what is used for

 * CC/CV charging. The maintenance charging will for safety reasons not go on

 * indefinately: we lower the current and voltage with successive maintenance

 * settings, then disable charging completely after we reach the last one,
@@ -385,14 +413,22 @@ struct power_supply_vbat_ri_table { 
 * ordinary CC/CV charging from there.

 *

 * As an example, a Samsung EB425161LA Lithium-Ion battery is CC/CV charged

 * at 900mA to 4340mV, then maintenance charged at 600mA and 4150mV for

 * 60 hours, then maintenance charged at 600mA and 4100mV for 200 hours.

 * at 900mA to 4340mV, then maintenance charged at 600mA and 4150mV for up to

 * 60 hours, then maintenance charged at 600mA and 4100mV for up to 200 hours.

 * After this the charge cycle is restarted waiting for

 * charge_restart_voltage_uv.

 *

 * For most mobile electronics this type of maintenance charging is enough for

 * the user to disconnect the device and make use of it before both maintenance

 * charging cycles are complete.

 * charging cycles are complete, if the current and voltage has been chosen

 * appropriately. These need to be determined from battery discharge curves

 * and expected standby current.

 *

 * If the voltage anyway drops to charge_restart_voltage_uv during maintenance

 * charging, ordinary CC/CV charging is restarted. This can happen if the

 * device is e.g. actively used during charging, so more current is drawn than

 * the expected stand-by current. Also overvoltage protection will be applied

 * as usual.

 */

struct power_supply_maintenance_charge_table {

	int charge_current_max_ua;