AFE4490 datasheet(33/70 Pages) TI

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LED

Current

Control

8-Bit Resolution

LED2 Current

Reference

LED1 Current

Reference

H-Bridge

Driver

H-Bridge

LED2_ON

LED1_ON

LED2_ON

LED1_ON

LED2 Current Reference

LED1 Current Reference

5-V Supply

ILED

CBULK

H-Bridge Supply

External

Supply

AFE4490

www.ti.com

SBAS602B – DECEMBER 2012 – REVISED FEBRUARY 2013

TRANSMIT SECTION

The transmit section integrates the LED driver and the LED current control section with 8-bit resolution. This

integration is designed to meet the specified dynamic range (based on a 1-sigma LED current noise).

The LED2 and LED1 reference currents can be independently set. The current source (ILED) locally regulates and

ensures that the actual LED current tracks the specified reference.

Two LED driver schemes are supported:

•

An H-bridge drive for a two-terminal back-to-back LED package, as shown in Figure 44. The minimum H-

bridge supply voltage must be 2.5 V + (maximum voltage drop across the LED).

•

A push-pull drive for a three-terminal LED package; see Figure 45. The minimum external supply voltage =

2.0 V + (maximum voltage drop across the LED). This value is the nominal value and depends on the registry

LED current settings (refer to the LED_RANGE[1:0] bits in the LEDCNTRL register).

Figure 44. Transmit: H-Bridge Drive

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