LM3530 datasheet(22/50 Pages) TI1

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0.73 mA

x 0.4

9.65

19 mA

BRT

LED

LED =

7.6 mA

x 0.4

.00

19 mA

BRT

LED

LED =

19 mA

x 100

.00

19 mA

BRT

LED

LED =

t > tPWM_HIGH(MAX)

t < tPWM_HIGH(MIN)

t < tPWM_LOW(MIN)

t > tPWM_LOW(MAX)

LM3530

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

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Figure 36. Simple Enable/Disable Timing

Example: Simple Enable Disable with PWM Current Control):

As an example, assume that the HWEN input is toggled low then high. This resets the LM3530 and sets all the

registers to their default value. When the PWM input is then pulled high for > 2 ms the LED current becomes:

where

•

BRT is the % of ILED_FS as set in the Brightness Control Register.

(4)

If then the PWM input is fed with a 5-kHz pulsed waveform at 40% duty cycle the LED current becomes:

(5)

Then, if the Brightness Control Register is loaded with 0x55 (9.6% of Full-Scale Current) the LED current

becomes:

(6)

8.3.14 Ambient Light Current Control

With bits [4:3] of the ALS Configuration Register both set to 1, the LM3530 is configured for Ambient Light

Current Control. In this mode the ambient light sensing inputs (ALS1, and/or ALS2) monitor the outputs of analog

output ambient light sensing photo diodes and adjust the LED current depending on the ambient light. The

ambient light sensing circuit has 4 configurable Ambient Light Boundaries (ZB0 – ZB3) programmed through the

four (8-bit) Zone Boundary Registers. These zone boundaries define 5 ambient brightness zones (Figure 27).

Each zone corresponds to a programmable brightness setting which is programmable through the 5 Zone Target

Registers (Z0T – Z4T). When the ALS1, and/or ALS2 input (depending on the bit settings of the ALS Input Select

bits) detects that the ambient light has crossed to a new zone (as defined by one of the Zone Boundary

Registers) the LED current becomes a function of the Brightness Code loaded in the Zone Target Register which

corresponds to the new ambient light brightness zone.

On start-up the 4 Zone Boundary Registers are pre-loaded with 0x33 (51d), 0x66 (102d), 0x99 (153d), and 0xCC

(204d). Each ALS input has a 1-V active input voltage range with a 4mV offset voltage which makes the default

Zone Boundaries set at:

Zone Boundary 0 = 1V × 51/255 + 4 mV = 204 mV

Zone Boundary 1 = 1V × 102/255 + 4 mV = 404 mV

Zone Boundary 2 = 1V × 153/255 + 4 mV = 604 mV

Zone Boundary 3 = 1V × 204/255 + 4 mV = 804 mV

These Zone Boundary Registers are all 8-bit (readable and writable) registers. The first zone (Z0) is defined

between 0 and 204 mV, the Z1 default is defined between 204 mV and 404 mV, the Z2 default is defined

between 404 mV and 604 mV, the Z3 default is defined between 604 mV and 804 mV, and the Z4 default is

defined between 804 mV and 1.004 V. The default settings for the 5 Zone Target Registers are 0x19, 0x33,

0x4C, 0x66, and 0x7F. This corresponds to LED brightness settings of 0.336%, 1.43%, 5.781%, 24.844%, and

100% of full-scale current respectively (assuming exponential backlight mapping).

Example: Ambient Light Control Current:

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