LM3530 datasheet(17/50 Pages) TI1

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LED Driver

BRT

ALS Select

VOUT

7 bits

LED Ramp

Rate Control

3 bits

Ramp Rate

Increasing

7 bits

DAC

Active Zone

Target

7 bits

Dig Code

3 bits

Ramp Rate

Decreasing

Full Scale

Current

1bit

Mapping Mode Select Bit

(0 = Exponental, 1 = Linear)

Full Scale Current Select Bits

LPF

PWM

EN_PWM bit

3 bits

PWM Polarity Bit

(0 = active high,

1 = active low)

Note 1

Note 2

Note 3

For EN_PWM bit = 1

ILED = IFS

ACODE

DPWM

For EN_PWM bit = 0

Note 3:

ILED = IFS

ACODE

DPWM Is a Scaler between 0 and 1 and corresponds to the duty cycle of the PWM input signal

Note 2:

ACODE Is a Scaler between 0 and 1 based on the Brightness Data or Zone Target Data Depending on the ALS Select Bit

Note 1:

LED

PWM

CODE

)

(

mA -

LM3530

www.ti.com

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

8.3.9 LED Current Control

The LED current is is a function of the Full Scale Current, the Brightness Code, and the PWM input duty cycle.

The Brightness Code can either come from the BRT Register (0xA0) in I2C-Compatible Current Control, or from

the ALS Zone Target Registers (Address 0x70-0x74) in Ambient Light Current Control. Figure 33 shows the

current control block diagram.

Figure 33. Current Control Block Diagram

8.3.10 Exponential or Linear Brightness Mapping Modes

With bit [1] of the General Configuration Register set to 0 (default) exponential mapping is selected and the code

in the Brightness Control Register corresponds to the Full-Scale LED current percentages in Table 2 and

Figure 34. With bit [1] set to 1 linear mapping is selected and the code in the Brightness Control Register

corresponds to the Full-Scale LED current percentages in Table 3 and Figure 35.

8.3.11 PWM Input Polarity

Bit [6] of the General Configuration Register controls the PWM input polarity. Setting this bit to 0 (default) selects

positive polarity and makes the LED current (with PWM mode enabled) a function of the positive duty cycle at

PWM. With this bit set to ‘0’ the LED current (with PWM mode enabled) becomes a function of the negative duty

cycle at PWM.

The PWM input is a logic level input with a frequency range of 400 Hz to 50 kHz. Internal filtering of the PWM

input signal converts the duty cycle information to an average (analog) control signal which directly controls the

LED current.

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