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AS7421

Functional Description

Datasheet

• PUBLIC

DS000667

• v2-00 • 2022-Oct-13

│ 16

Functional Description

Upon power-up (POR), the device initializes. It is required that VDD is applied and settled 10 ms

before the supply voltage of the NIR light source is applied (VLED_A). During power down VLED_A

needs to be turned off 10 ms prior VDD.

During initialization, the device cannot accept I²C transactions. All communication with the device must

be delayed and all outputs from the device must be ignored including interrupts. After initialization, the

device enters the SLEEP state. In this operational state, the internal oscillator and other circuitry are

not active, resulting in ultra-low power consumption. If an I²C transaction occurs during this state, the

I²C core wakes up temporarily to service the communication. Once the Power ON bit,

“PON”, is

enabled, the device enters the IDLE state in which the internal oscillator and attendant circuitry are

active, but power consumption remains low. Whenever the spectral measurement is enabled

(LTF_ON =

“1”) the device enters the ACTIVE state. If the spectral measurement is disabled

(LTF_ON =

“0”) the device returns to the IDLE state. The figure below describes a simplified state

diagram and the typical supply currents in each state. The power consumption in ACTIVE state does

not include the power consumption to drive the NIR LEDs.

Figure 12:

Start Up Flow-Chart

Power On

VDD > VDD_POR

Reg 0x60 bit

PON = „1"

Reg 0x60 bit

LTF_ON = „1"

SLEEP

IDD = 2µA (typ)

IDLE

IDD = 200µA (typ)

ACTIVE

Spectral measurement

IDD = 2.5mA (typ)

AS7421 Datenblatt(PDF) 17 Page - ams-OSRAM AG