AFE4490 datasheet(34/69 Pages) TI

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50 PA

0 mA to 50 mA

(See the LEDRANGE bits

in the LEDCNTRL register.)

LED_ON

1 PA

TX_CTRL_SUP_3.3V

LED_DRV_SUP_3.3V

Device

Tx LED

Bridge

LED

Current

Control

DAC

Tx Reference

and

Control

AFE4400

SBAS601D – DECEMBER 2012 – REVISED MAY 2013

www.ti.com

Transmitter Power Path

The block diagram in Figure 48 shows the AFE4400 Tx subsystem power routing.

Figure 48. Transmit Subsystem Power Routing

LED Power Reduction During Periods of Inactivity

The diagram in Figure 49 shows how LED bias current passes 50 µA whenever LED_ON occurs. In order to

minimize power consumption in periods of inactivity, the LED_ON control must be turned off. Furthermore, the

TIMEREN bit in the CONTROL1 register should be disabled by setting the value to '0'.

Note that depending on the LEDs used, the LED may sometimes appear dimly lit even when the LED current is

set to 0 mA. This appearance is because of the switching leakage currents (as shown in Figure 49) inherent to

the timer function. The dimmed appearance does not effect the ambient light level measurement because during

the ambient cycle, LED_ON is turned off for the duration of the ambient measurement.

Figure 49. LED Bias Current

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AFE4490 Datasheet(PDF) 34 Page - Texas Instruments