LM3530 datasheet(23/50 Pages) TI1

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13 mA

26 mA x 100% x 50%

ZoneTarget5 x D =

LED

LED =

1.5 mA

26 mA x 5.781%

ZoneTarget2 =

LED

LED =

ILED = ILED_FS u ZoneTarget0 = 26 mA u 0.336% | 87 PA.

LM3530

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SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

As an example, assume that the APDS-9005 is used as the ambient light sensing photo diode with its output

connected to the ALS1 input. The ALS Resistor Select Register is loaded with 0x04 which configures the ALS1

input for a 2.27-k

Ω internal pull-down resistor (see Table 9). The APDS-9005 has a typical 400nA/LUX response.

With a 2.27-k

Ω resistor the sensor output would see a 0-mV to 908-mV swing with a 0 to 1000 LUX change in

ambient light. Next, the ALS Configuration Register is programmed with 0x3C. From Table 6, this configures the

LM3530’s ambient light sensing interface for:

ALS1 as the active ALS input (bits [6:5] = 01)

Ambient Light Current Control Enabled (bit 4 = 1)

ALS circuitry Enabled (bit 3 = 1)

Sets the ALS Averaging Time to 512 ms (bits [2:0] = 100)

Next, the General Configuration Register is programmed with 0x19 which sets the Full-Scale Current to 26 mA,

selects Exponential Brightness Mapping, and enables the device via the I2C-compatible interface.

Now assume that the APDS-9005 ambient light sensor detects a 100 LUX ambient light at its input. This forces

the ambient light sensors output (and the ALS1 input) to 87.5mV corresponding to Zone 0. Since Zone 0 points

to the brightness code programmed in Zone Target Register 0 (loaded with code 0x19), the LED current

becomes:

(7)

Where the code in Zone Target Register 0 points to the % of ILED_FS as given by Table 2 or Table 3,

depending on whether Exponential or Linear Mapping are selected.

Next, assume that the ambient light changes to 500 LUX (corresponding to an ALS1 voltage of 454 mV). This

moves the ambient light into Zone 2 which corresponds to Zone Target Register 2 (loaded with code 0x4C) the

LED current then becomes:

(8)

8.3.15 Ambient Light Current Control + PWM

The Ambient Light Current Control can also be a function of the PWM input duty cycle. Assume the LM3530 is

configured as described in the above Ambient Light Current Control example, but this time the Enable PWM bit

set to ‘1’ (General Configuration Register bit [5]).

Example: Ambient Light Current Control + PWM

In this example, the APDS-9005 detects that the ambient light has changed to 1 kLUX. The voltage at ALS1 is

now around 908 mV, and the ambient light falls within Zone 5. This causes the LED brightness to be a function

of Zone Target Register 5 (loaded with 0x7F). Now assume the PWM input is also driven with a 50% duty cycle

pulsed waveform. The LED current now becomes:

(9)

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