TOUCH CONTROL CONTINUOUS DIMMER with

AUTOMATIC GAIN CONTROL (AGC)

FEATURES:

• Touch or pushbutton control of incandescent lamps.

• Touch Sensitivity guaranteed to 600pF Touch Plate Capacitance.

• Touch Operation independent of line plug polarity.

• Minimal external components.

• AGC Loop stabilizes immediately after Power-Up.

• Brightness state is Off after AC power applied.

• No change of Brightness state if AC power interrupted < 0.5 sec

• Advanced CMOS design for reliable operating characteristics

and low power.

• 50/60 Hz Line Frequency.

• LS7540 (DIP); LS7540-S (SOIC) - See Figure 1 -

APPLICATIONS:

• Screw-in and built-in adapter modules for converting table

and floor lamps to touch control for continuous dimming.

PIN ASSIGNMENT

TOP VIEW

June 2006

7540-060906-1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

LS7540

DESCRIPTION:

The LS7540 is a CMOS integrated circuit for controlling the

brightness of incandescent lamps with momentary touch. When

its TOUCH input is connected to a lamp body, the entire lamp

turns into a touch plate. A built-in AGC circuit allows for a wide

range of lamp sizes to be used, ranging from very small table

lamps to very large floor lamps. The brightness is controlled by

controlling the conduction angle of a triac in series with the lamp

and triggered by the TRIG/ output. Between off and maximum,

there are 124 steps of brightness levels, level zero being off and

level 124 being maximum. The phase reference of the Trig/ sig-

nal with respect to the AC line is maintained through the SYNC

input.

Touch Operation

The on/off and brightness control of the lamp is made with brief

touches of the lamp body as described below:

• In the off state a single touch will turn the lamp to full_on.

• At full-on a single touch will start a dim-cycle causing the

brightness to diminish gradually until the lamp turns off.

• During a dim-cycle a single touch will stop the dim-cycle and

lock in the brightness present at that time. Another touch will re-

start the dim-cycle from the present brightness causing the

brightness to ramp down towards off again. The start and stop of

dim-cycle can be repeated over and over again until the lamp

turns off.

CLOCK Input (Pin 1)

with an internal capacitor and oscillator stage, generates a clock

which is used for all timing functions. The recommended value of

this resistor for 50Hz and 60Hz operation is specified in the

ELECTRICAL CHARACTERISTICS.

SYNC Input (Pin 2)

50Hz or 60Hz AC input for zero crossing detection.

TOUCH Input (Pin 4)

Input for sensing that a touch has been made on a lamp surface or

other touch plate. This action alters the state of the TRIG output as

described in the Touch Operation section of the General De-

scription.

CONTROL I/O (Pin 5)

tablishes the controlling feedback for the AGC Loop.

RAMP Input/Output (Pin 6)

The ramp down rate of the brightness in the dimming cycle is regu-

lated by a resistor-capacitor (RC) pair connected to the RAMP in-

Example:

R = 200k

Ω, C = 0.22uF;

TRIG/ output (Pin 8)

The TRIG/ output produces a negative pulse every half cycle of

the AC line period to turn on a triac in series with the lamp or any

other load device. The brightness of the lamp is regulated by regu-

lating the conduction angle, Ø (See Fig. 2) of the TRIG/ signal.

The conduction angles at maximum brightness (level 124) and

mimimum brightness (level 1) are 162° and 50° with 0.91° in-

cremental steps.

UL

®

A3800

1

2

3

4

8

7

6

5

FIGURE 1

RAMP

CONTROL

SYNC

CLOCK

TOUCH

TRIG/