LM3530 datasheet(12/50 Pages) TI1

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A/D

Vdd

Vsns

Averager

(LPF)

LED Driver

Z 4 target light

Z0 target light

Z1 target light

Z 2 target light

Z 3 target light

Brightness

ALS Select

VOUT

Light output

Targets for

Each of 5

Ambient

Light zones

User Selectable w/

Typical Defaults

Zone

Discriminator

Ramp

control

3 bits

Ramp Rate

Selection

ALS Path Functional Diagram

Zline

ALSRS

ALS Resistor

Select Register

8 bits

7 bits

User Selectable w/

Typical Defaults

Input

Light

Zone

Definiton

Registers

LM3530

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

www.ti.com

8.3 Feature Description

8.3.1 Start-Up

An internal soft-start prevents large inrush currents during start-up that can cause excessive current spikes at the

input. For the typical application circuit (using a 10-µH inductor, a 2.2-µF input capacitor, and a 1-µF output

capacitor) the average input current during start-up ramps from 0 to 300 mA in 3 ms. See Figure 22 in the

Typical Characteristics.

8.3.2 Light Load Operation

The LM3530 boost converter operates in three modes: continuous conduction, discontinuous conduction, and

skip mode. Under heavy loads when the inductor current does not reach zero before the end of the switching

period, the device switches at a constant frequency (500 kHz typical). As the output current decreases and the

inductor current reaches zero before the end of the switching period, the device operates in discontinuous

conduction. At very light loads the LM3530 will enter skip mode operation causing the switching period to

lengthen and the device to only switch as required to maintain regulation at the output. Light load operation

provides for improved efficiency at lighter LED currents compared to continuous and discontinuous conduction.

This is due to the pulsed frequency operation resulting in decreased switching losses in the boost converter.

8.3.3 Ambient Light Sensor

The LM3530 incorporates a dual input Ambient Light Sensing interface (ALS1 and ALS2) which translates an

analog output ambient light sensor to a user-specified brightness level. The ambient light sensing circuit has 4

programmable boundaries (ZB0 – ZB3) which define 5 ambient brightness zones. Each ambient brightness zone

corresponds to a programmable brightness threshold (Z0T – Z4T). The ALS interface is programmable to accept

the ambient light information from either the highest voltage of ALS1 or ALS2, the average voltage of ALS1 or

ALS2, or selectable from either ALS1 or ALS2.

Furthermore, each ambient light sensing input (ALS1 or ALS2) features 15 internal software selectable voltage

setting resistors. This allows the LM3530 the capability of interfacing with a wide selection of ambient light

sensors. Additionally, the ALS inputs can be configured as high impedance, thus providing for a true shutdown

during low power modes. The ALS resistors are selectable through the ALS Resistor Select Register (see

Table 9). Figure 26 shows a functional block diagram of the ambient light sensor input. VSNS represents the

active input as described in Table 6 bits [6:5].

Figure 26. Ambient Light Sensor Functional Block Diagram

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