9

FN6282.1

September 21, 2010

resistor at the output. This limit is set by the design of the

internal metal interconnects.

ISL29008 has the capability of both sourcing and sinking

current simultaneously. It may replace ISL29006 in sourcing

current applications, or ISL29007 in sinking current

applications. In applications that require both sourcing and

sinking currents, for example in cases of mobile phones or

PDAs where the display brightness needs to be proportional

to ambient brightness while the key pads need to be

inversely proportional to the brightness, ISL29008 offers the

most economical solution for cost and footprint.

Suggested PCB Footprint

Footprint pads should be a nominal 1-to-1 correspondence

with package pads. Since ambient light sensor devices do

not dissipate high power, heat dissipation through the

exposed pad is not important; instead, similar to DFN or

QFN, the exposed pad provides robustness in the board

mounting process. Therefore, we recommend that the

exposed pad be soldered down for robust joint formation, but

this is not mandatory.

Power Supply Bypassing and Printed Circuit

Board Layout

The ISL29006, ISL29007 and ISL29008 are relatively

insensitive to the printed circuit board layout due to their low

speed operation. Nevertheless, good printed circuit board

layout is necessary for optimum performance. Ground plane

construction is highly recommended; lead length should be

as short as possible and the power supply pins must be well

bypassed to reduce the risk of oscillation. For normal single

supply operation where the GND pin is connected to ground,

a 0.1µF ceramic capacitor should be placed from the VCC

pin to the GND pin. A 4.7µF tantalum capacitor should then

be connected in parallel, placed close to the device.

Optical Sensor Location Outline

The green area in Figure 22 shows the optical sensor

location outline of ISL29006, ISL29007 and ISL29008.

Along the pin-out direction, the center line (CL) of the sensor

coincides with that of the packaging. The sensor width in this

direction is 0.39mm. Perpendicular to the pin-out direction,

the CL of the sensor has a 0.19mm offset from the CL of

packaging away from pin-1. The sensor width in this

direction is 0.46mm.

LX

FB

ENABLE

VIN

U2

EL7630

6.19

L1

22µH

C2

1µF

R1

100k

VIN

ENABLE

C1

1µF

D1

MA2772800LCT-ND

GND

Rs

750

VDD

1

GND

2

NC

ISRC

6

U1

ISL29006 LIGHT SENSOR

C2

0.1µF

D4

D5

D6

D3

D2

FIGURE 21. AUTOMATIC DIMMING CONTROL

5

NC

3

EN

4

I

LED

V

FB

R

LED

---------------

E

1.6

μA

100lux

-------------------

⎝⎠

⎛⎞

R

S

R

LED

---------------

1

+

⎝⎠

⎜⎟

⎛⎞

•

•

–

=

(EQ. 7)

ISL29006, ISL29007, ISL29008