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AS73211

Functional Description

Datasheet

• PUBLIC

DS000556

• v3-01 • 2018-Feb-07

│ 29

MRES: Digital output value of the conversion (content of output registers MRES1 to MRES3)

Ee: Input light irradiance regarding to the photodiode’s area within the conversion time interval

FSREe: Full Scale Range of detectable input light irradiance Ee

Re: Irradiance responsivity (see Figure 14)

TCONV: Conversion time interval

NCLK: Number of clock cycles within the conversion time interval TCONV (see Figure 13)

fCLK: Clock frequency

In the CONT, CMD and SYNS modes the conversion time TCONV is internally generated1.In the SYND

mode the conversion time is defined by the timing of the external pulses at SYN pin and the number of

pulses stored in the register EDGES (see Figure 19

chapter “Conversion time measurements in SYND

mode” and chapter “Register - EDGES”).

The number of clock counts within this interval is a constant number, which keeps the output result

independent of the internal clock frequency. In this case the input light irradiance Ee regarding to the

photodiodes area of the channel can be represented by the Equation 1. In SYND mode, the Equation

2 represents the externally generated conversion time TCONV and the conversion result. If the

conversion time measurement is activated (CREG2

:EN_TM = ‚1‘) the number of clock counts within

the externally given conversion time can also be internally captured. So the input light irradiance Ee

regarding to the photodiode’s area of the channel can be calculated as:

Equation 3:

MRES

OUTCONV

FSR





MRES: Digital output value of the conversion (content of output registers MRES1 to MRES3)

Ee: Input light irradiance regarding to the photodiode’s area within the conversion time interval

FSREe: Full Scale Range of detectable input light irradiance Ee

OUTCONV: Conversion time duration expressed as the number of clock counts within this time.

In this way, the input light irradiance can be measured independently of the internal frequency and

furthermore external conversion time variations in SYND mode.

The calculation of the input light irradiance by Equation 3 is more precise than the result of Equation 2

because the tolerances of the clock frequency fCLK are eliminated. The irradiance responsivity Re and

1 The system clock is internally generated and is subject to technological tolerances. So the clock frequency may vary, which

must be considered when calculating the time to be programmed (e. g. registers BREAK for pause time TBREAK or

CREG1:TIME for conversion time TCONV).

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