LSI LS7237-S, LS7237 Datasheet

TOUCH CONTROL LAMP STEP DIMMER

DESCRIPTION:

LS7237 is a monolithic, MOS integrated circuit designed
to control the brightness of an incandescent lamp. The
output of the LS7237 triggers a triac connected in series
with a lamp(See Figure 5). The lamp brightness is de­termined by controlling the output conduction angle (triac
triggering angle) in relation to the AC line frequency (See
Figure 2).

The output conduction angle can be varied by applying a
low level pulse at the SENS input or a high level pulse at
the EXT input. When implemented as shown in Figure 5,
this is accomplished by touching the Touch Plate which
causes the lamp brightness to change in specified steps
as follows:

LEVEL BRIGHTNESS (% Rated Wattage)

Off 0
Night Light 9
Mood Light 29
Medium 66
Maximum 99

The LS7237 can operate in one of three different modes
selected by the MODE input. The Brightness Sequences
produced by the different modes are as follows:

MODE BRIGHTNESS SEQUENCE

0 Off-Max-Off
1 Off-Mood-Med-Max-Off
2 Off-Night-Mood-Med-Max-Off

After AC power-up, the output comes up in the OFF state.
Following that, every time the Touch Plate is touched, the
output steps to the next level of brightness. The next step
following the maximum brightness is the OFF state, in­itiating a new sequence.

1

2

3

4

8

7

6

5

LS7237

V

DD

(-V)

MODE

CAP

SYNC

TRIG

V

SS

(+V)

EXT

SENS

FIGURE 1

PIN ASSIGNMENT - TOP VIEW

LSI

7237-041100-1

April 1995

INPUT/OUTPUT DESCRIPTION:

VSS (Pin 1)

Supply voltage positive terminal.

MODE (Pin 2)

The operating mode for the circuit is selected by con­necting this input as follows:

MODE INPUT SELECTED MODE

VSS Mode 0
VDD Mode 1
Float Mode 2

CAP (Pin 3)

PLL filter input capacitor. A 0.047µF capacitor should be
connected to this input.

SYNC (Pin 4)

The AC Line Frequency is applied to this input through an
external RC circuit (See Figure 5). The Phase-Lock Loop
in the IC synchronizes all internal timings to the AC signal
at the SYNC input.

SENS (Pin 5)

A low-level pulse applied to this input causes the TRIG out­put to step to the next conduction angle in the sequence
selected by the MODE input. The change in conduction an­gle takes place with the trailing edge of the SENS input
pulse.

FEATURES:

• PLL synchronization allows use as a Wall Switch

• Provides brightness control of an incandescent lamp
with a touch plate or mechanical switch

• Can control speed of shaded pole and universal AC motors

• Controls the "duty cycle" from 23% to 88% (conduction
angles for AC half-cycles between 45˚ and 158˚, respectively)

• Operates at 50Hz/60Hz line frequency

• Extension input for remote activation

• +12V to +18V DC Power Supply (VSS - VDD)

• 8-Pin Plastic DIP , 8-Pin SOIC-See Figure 1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 [phone] FAX [phone]

LS7237

U

L

®

A3800

The information included herein is believed to be
accurate and reliable. However, LSI Computer Systems,
Inc. assumes no responsibilities for inaccuracies, nor for
any infringements of patent rights of others which may
result from its use.

CONDUCTION ANGLE, Ø BRIGHTNESS LEVEL

No output Off

45˚ Night Light

70˚ Mood Light
105˚ Medium
158˚ Maximum

NOTE: In the schematic shown in Figure 5, the SYNC Input sig­nal is delayed in phase with respect to the AC Line by about 7°.
This delay reduces the conduction angle, Ø with respect to the
AC Line by 7° from the values shown above.

7237-041395-2

ø

TRIG

SYNC

TW

TW

FIGURE 2. TRIG OUTPUT CONDUCTION ANGLE, Ø

EXT (Pin 6)

The EXT input is functionally similar to the SENS input with
the exception that a high-level pulse is the active signal. It is
recommended that the EXT input be used instead of the
SENS input when long extension wires are used between the
IC and the sensing circuitry (See Figure 5 and Figure 6) be­cause the EXT input is less susceptible to “Noise”.

VDD (Pin 7)

Supply voltage negative terminal.

TRIG (Pin 8)

The TRIG output is a low-level pulse of fixed duration oc­curring once every half-cycle of the SYNC input. The con­duction angle, Ø of the output in relation to the SYNC signal
controls the lamp brightness. The 5 levels of brightness cor­respond to the 5 values of Ø as follows:

SENS

Ø, MODE 0

Ø, MODE 1

Ø, MODE 2

TS1

OFF

OFF

OFF

70˚

45˚

OFF

105˚

70˚

158˚

158˚

105˚

OFF

OFF
158˚

158˚

70˚

OFF

FIGURE 3. TRIG OUTPUT CONDUCTION ANGLE, Ø, VS SENS INPUT

158˚