RT9481 datasheet(21/41 Pages) RICHTEK

21 / 41 page

RT9481

is a registered trademark of Richtek Technology Corporation.

DS9481-00 June 2015

www.richtek.com

ADC Conversion Operation Flow

Figure 4 shows ADC conversion operation flow. ADC

conversion starts from set ADC channel CH_SEL

(ADC_CLT[7:5]) and set ADC_START (ADC_CLT[0])

high.

ADC

conversion

time

25ms

and

ADC_DONEI (MISC_IRQ[7]) will set to high and

ADC_STAT (MISC_STAT1) will set to low also, the

host could read them to make sure ADC conversion

completes.

The

host

could

read

ADC

code

high

byte

(ADC_CODEH[7:0]) and low byte (ADC_CODEL[7:0])

to calculate the voltage or current measurement

relative to ADC channel.

Table 9 shows the every measurement equation of ADC

channel. Please pay attention to the calculation of IRS, it

need to consider the setting of ICHG (CHG_CTRL6[7:4]).

ADC code format is unsigned. If operation is Charger

mode, IVRS means battery charging current. If

operation

boost

mode,

IRS

means

battery

discharging current.

The code of

IRS is invalid if SWITCHING_EN

(CHG_STA1[0]) is set to low. And the code of

IUSBOUT is invalid if EN_LDSW (USBOUT_CTL[6]) is

set to low.

The TS pin will automatic output 35uA during ADC TS

channel under conversion. It will cause the IR drop on

NTC thermistor and then ADC measure the voltage on

TS pin. The host could get the temperature by

mapping the voltage. We suggest to use 10k

 NTC

which the beta (B25/85) is 3435k, like SEMITEC

103AT.

Table 9. Calculate Voltage or Current Measurement

ADC Channel

Measurement Equation

Measurement Range

VBAT

VBAT = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x 1.25 mV

0V to VDDA

VBUS

VBUS = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x 6.25 mV

1V to 18V

USBOUT

USBOUT = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x 6.25 mV

1V to 6V

TS = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x 1.25 mV

0V to VDDA

IRS

IRS = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x ICHG x 1.25 mA

0A to 6A

IUSBOUT

IUSBOUT = ( ( ADC_CODEH x 256 ) + ADC_CODEL ) x 2.5 mA

0A to 6A

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