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Supported chips:
  * Dialog Semiconductors DA9052-BC and DA9053-AA/Bx PMICs
    Prefix: 'da9052'
    Datasheet: Datasheet is not publicly available.

Authors: David Dajun Chen <dchen@diasemi.com>

Description
-----------

The DA9052/53 provides an Analogue to Digital Converter (ADC) with 10 bits
resolution and track and hold circuitry combined with an analogue input
multiplexer. The analogue input multiplexer will allow conversion of up to 10
different inputs. The track and hold circuit ensures stable input voltages at
the input of the ADC during the conversion.

The ADC is used to measure the following inputs:
Channel 0: VDDOUT - measurement of the system voltage
Channel 1: ICH - internal battery charger current measurement
Channel 2: TBAT - output from the battery NTC
Channel 3: VBAT - measurement of the battery voltage
Channel 4: ADC_IN4 - high impedance input (0 - 2.5V)
Channel 5: ADC_IN5 - high impedance input (0 - 2.5V)
Channel 6: ADC_IN6 - high impedance input (0 - 2.5V)
Channel 7: XY - TSI interface to measure the X and Y voltage of the touch
	   screen resistive potentiometers
Channel 8: Internal Tjunc. - sense (internal temp. sensor)
Channel 9: VBBAT - measurement of the backup battery voltage

By using sysfs attributes we can measure the system voltage VDDOUT, the battery
charging current ICH, battery temperature TBAT, battery junction temperature
TJUNC, battery voltage VBAT and the back up battery voltage VBBAT.

Voltage Monitoring
------------------

Voltages are sampled by a 10 bit ADC.

The battery voltage is calculated as:
	Milli volt = ((ADC value * 1000) / 512) + 2500

The backup battery voltage is calculated as:
	Milli volt = (ADC value * 2500) / 512;

The voltages on ADC channels 4, 5 and 6 are calculated as:
	Milli volt = (ADC value * 2500) / 1023

Temperature Monitoring
----------------------

Temperatures are sampled by a 10 bit ADC.  Junction and battery temperatures
are monitored by the ADC channels.

The junction temperature is calculated:
	Degrees celsius = 1.708 * (TJUNC_RES - T_OFFSET) - 108.8
The junction temperature attribute is supported by the driver.

The battery temperature is calculated:
	Degree Celsius = 1 / (t1 + 1/298)- 273
where t1 = (1/B)* ln(( ADCval * 2.5)/(R25*ITBAT*255))
Default values of R25, B, ITBAT are 10e3, 3380 and 50e-6 respectively.