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AS7421

Functional Description

Datasheet

• PUBLIC

DS000667

• v1-00 • 2022-Aug-25

│ 20

7.6

LED Driver

Four current sinks are provided to drive the 4 integrated NIR LEDs with a programmable constant

current of 50 mA or 75 mA per channel. If a measurement is done with 4 x 75 mA ILED the next

measurement can be started after a timeout of 10 seconds.

The LED driver can be configured with the register CFG_LED. With the bits

“LED_AUTO” in register

0x60 it is possible that the LED driver is configured in such a way that during two consecutive spectral

measurements the LEDs are turned on in the first and turned off in the second measurement or vice

versa. The example below shows how the device needs to be configured to turn on all LEDs for

integration cycle A to D.

Figure 18:

LED Configuration Example

– All LEDs On During Integration

LED cycle A

Reg CFG_LED; Bit LED_OFFSET = 0

Reg CFG_MULT = 0x1F

LED cycle B

Reg CFG_LED; Bit LED_OFFSET = 1

Reg CFG_MULT = 0x1F

LED cycle C

Reg CFG_LED; Bit LED_OFFSET = 2

Reg CFG_MULT = 0x1F

LED cycle D

Reg CFG_LED; Bit LED_OFFSET = 3

Reg CFG_MULT = 0x1F

SLEEP

IDD = 2µA (typ)

Reg 0x60 bit

PON = 1"

ACTIVE

Spectral measurement

IDD = 2.5mA (typ)

Reg 0x60

Bit LED_AUTO = 11" ; LTF_EN = 1"

PON = 1"

LED current

Reg CFG_LED; Bit LED_CURRENT

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