The charger hardware has a +/-30mv error for vdd_max settings. This
means that when vdd_max is set to 4200mV the actual voltage on vph_pwr
line could range from 4170mV to 4230mV. This further means that when
constant current to constant voltage transition happens, the battery
may not be charged up to 4200mV - leading to an premature end of charge.
Fix this by implementing periodic IR compensation. On a device measure the
resistance from the vbat terminal to the ground by shorting the +ve and
-ve of the battery terminals (without a battery), this will be referred to
as rconn in the description. In the code it is rconn_mohm to reflect the
units.
The voltage at battery terminal will be
Vbat(terminal) = Vbat(xoadc) + Ibat * rconn
where Ibat is the current flowing out of (or into if -ve) of the battery.
Vbat(xoadc) and Ibat can be obtained by using the override mode of the
bms. So Vbat(terminal) can be deduced and compensated by increasing
vdd_max. This also helps in increasing constant current mode thereby
decreasing constant voltage mode and decreasing the overall charging time.
The value of rconn will be specific to a PCB layout, it is
passed in from platform_data.
Change-Id: If8df93333ca6b0bad35505895a4fc5577562fadd
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
40491ce8d0