PROXIMITY/TOUCH CONTROL HALOGEN LAMP DIMMER

DESCRIPTION:

LS7232NT is a CMOS integrated circuit designed for brightness

control of incandescent lamps or tranformer coupled low voltage

halogen lamps. The brightness is controlled by controlling the fir-

ing angle of a triac in series with the lamp and triggered by the

LS7232NT. A Phase-Locked-Loop keeps the LS7232NT phase

pointer locked in phase with the line voltage.

A unique optical user interface provides for a smooth control of

the lamp intensity without the need for touching any sensor

plate. A mechanical switch interface for dimming control is also

provided which can be used for a remote touch plate. The IC in-

cludes features to address problems associated with inductive

loads such as transformers in low voltage halogen lamp applica-

tion. The voltage to current phase lag resulting from the in-

ductance may prevent the triac from shutting off at AC zero

crossover and/or prevent the triac from maintaining conduction

following the removal of the gate trigger.

These problems are addressed by the LS7232NT in the fol-

lowing manner:

1. Compensation for delayed triac cut-off.

When trigger pulse is due to occur at a conduction angle

which coincides with the on-state of the triac, the trigger

pulse is delayed until the triac has turned off. This elim-

inates the underlying cause of half-waving.

2. Compensation for delayed triac turn-on.

At the set conduction angle, a triac trigger pulse of 130.2µs

(60Hz) is issued by the dimmer IC. If the triac fails to fire, a

second trigger pulse of 260.4µs width is issued a milli-

second later as a second attempt to fire the triac during the

same half-cycle.

3. Safety-Shutdown.

If the frequency of occurrences of the delayed cut-off and

the delayed turn-on exceeds a preset threshold, a shut-

down is initiated by turning off the triac trigger pulses. The

safety-shutdown threshold value is accumulated in a 4-bit

Up/Down counter. The count increments for every oc-

currence of delayed cut-off or delayed turn-on and decre-

ments once every 8 SYNC pulses (AC line cycles). The

count will not decrement below zero. If the count reaches

15, the safety-shut-down is effected.

PIN ASSIGNMENT - TOP VIEW

1

2

3

4

5

6

7

8

9

10

11

12

13

14

LS7232NT

CAP

SYNC

ANODE

CATHODE

PHOTOUT

SENS

REMOTE

M2

M1

RC

LEDO

TRIG/

Vss (-V)

FIGURE 1

The LS7232NT can be configured in 7 different modes of dim-

ming and timing off functions selected by two 3-state mode

pins.

INPUT/OUTPUT DESCRIPTION:

CAP (Pin 1)

PLL filter capacitor input. A 0.02µF capacitor is required at this

input for the optimal operation of the PLL.

SYNC (Pin 2)

The phase pointer for the triac trigger signal is synchronized

with the 50Hz/60Hz AC voltage applied at the SYNC input by

the internal PLL. The triac On/Off status information is also de-

rived from this input.

ANODE (Pin 3) CATHODE (Pin 4) and PHOTOUT (Pin 5)

These three pins constitute the input/outputs of a trans-

conductance and voltage amplifier pair (See Fig. 6) for con-

verting the current from a photo-diode to a voltage stimulus for

application at the SENS input. The photo-signal is used in lieu

of a touch plate for a touchless dimmer system. The output at

PHOTOUT is governed by the following equation:

ANODE and CATHODE

and CATHODE

the photo-amplifier system.

7232NT-111501-1

November 2001

FEATURES:

•

Control of incandescent and transformer coupled

halogen lamps.

•

No-Touch lamp control through optical sensing

•

PLL synchronization of AC for wall switch application.

•

Extension input for remote control

•

Safety-shutdown for transformer malfunction.

•

Pin-selectable operating modes

•

Single 5V power supply

•

50Hz/60Hz AC line frequency

•

LS7232NT (DIP), LS7232NT-S (SOIC) - See Figure 1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747

(631) 271-0400 FAX (631) 271-0405

LS7232NT

UL

®

A3800