Datasheet LS7237-S, LS7237 Datasheet (LSI)

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˚

ABSOLUTE MAXIMUM RATINGS:

PARAMETER SYMBOL VALUE UNIT

DC Supply Voltage VSS +20 V
Any Input Voltage VIN VSS -20 to VSS +0.5 V
Operating Temperature TA 0 to +80 ˚C
Storage Temperature TSTG -65 to +150 ˚C

DC ELECTRICAL CHARACTERISTICS:

(TA = 25˚C, all voltages referenced to VDD)

PARAMETER SYMBOL MIN TYPE MAX UNIT CONDITION

Supply Voltage VSS +12 – +18 V -
Supply Current ISS – 1.0 1.4 mA VSS = +15V,

output off

Input Voltages:
MODE LO VIZL 0 – VSS-9 V -
MODE HI VIZH VSS-1.5 – VSS V -
SYNC LO VIRL 0 – VSS-9.5 V -
SYNC HI VIRH VSS-5.5 – VSS V -
SENS LO VIOL 0 – VSS-8 V -
SENS HI VIOH VSS-2 – VSS V -
EXT LO VIVL 0 – VSS-8 V -
EXT HI VIVH VSS-2 – VSS V -

Input Current:
SYNC, SENS, EXT HI IIH – – 110 µA With Series 1.5MΩ

Resistor to
115VAC Line

SYNC, SENS, EXT LO IL – – 100 nA -
TRIG HI Voltage VOH – VSS – V -

TRIG LO Voltage VOL – VSS-8 – V VSS = +15V
TRIG Sink Current IOS 25 – – mA VSS = +15V

VOL = VSS-4V

TIMING CHARACTERISTICS (See Figures 2 and 3):
All timings are based on fs = 60Hz, unless otherwise specified. 50Hz timings are 1.2 times 60Hz timings.

PARAMETER SYMBOL MIN TYPE MAX UNIT
SYNC Frequency fs 40 - 70 Hz
SENS/EXT Duration TS1 50 - Infinite ms

TRIG Pulse Width TW - 33 - µs

7237-041395-3

OUTPUT
DRIVER

DIGITAL
COMPARATOR

Ø

MEMORY

PHASE
LOCK
LOOP

CONTROL
LOGIC

BUF

BUF

BUF

BUF

SYNC

CAP

MODE

EXT

SENS

VSS

VDD

FIGURE 4

LS7237 BLOCK DIAGRAM

4
3

2

6

5

1
7

(+V)

(-V)

8

TRIG

Ø

POINTER

C1 = 0.15µF,200V R4 = 1MΩ to 5MΩ,1/4W
C2 = 0.33µF,200V (Select for sensitivity)
C3 = 0.047µF,25V R5, R6 = 2.7MΩ,1/4W
C4 = 470pF,25V R7 = 150KΩ,1/4W
C5 = 47µF,25V R8 = 100Ω,1/4W
C6 = 680pF,25V D1 = IN4148
C7 = 0.1µF,25V Z = 15V,1W (Zener)
R1 = 270Ω,1W T = Q4006L4 Triac (Typical)
R2 = 1.5MΩ,1/4W L = 100µH (RFI Filter)
R3 = 1.5MΩ,1/4W

(1) For Connection A. Use 0.22µF for Connection B.
(2) For Connection A, Modes 1 and 2. Use 1/4W for Mode 0
and Connection B, all Modes.

C1 = 0.15µF,400V R4 = 1MΩ to 5MΩ,1/4W
C2 = 0.22µF,400V (Select for sensitivity)
C3 = 0.047µF,25V R5, R6 = 4.7MΩ,1/4W
C4 = 470pF,25V R7 = 150KΩ,1/4W
C5 = 47µF,25V R8 = 100Ω,1/4W
C6 = 680pF,25V D1 = 1N4148
C7 = 0.1µF,25V Z = 15V,1W (Zener)
R1 = 1KΩ, 2W T = Q5004L4 Triac (Typical)
R2 = 1.5MΩ,1/4W L = 200µH (RFI Filter)
R3 = 1.5MΩ,1/4W

(3) For Connection A. Use 0.1µF for Connection B.
(4) For Connection A, Modes 1 and 2. Use 1/4W for Mode 0
and Connection B, all Modes.

NOTES:

P

115VAC

OR

220VAC

N

LOAD

C1

T

L

C2

R1

R2
A
B

R8

R3

C5

D1

1 2 3 4

8 7 6 5

R4

C3 C4

TRIG VDD EXT SENS

VSS MODE CAP SYNC

+

SEE NOTE 3

LS7237

R6 R5

FIGURE 5. A Typical Lamp Dimmer

G

Z

-

ELECTRONIC
EXTENSION
(FIG. 6)

EXTN

P

C7

SEE NOTE 4

SEE NOTE 2

R7

C6

TOUCH
PLATE

MT2

MT1

1) All circuits connected by broken lines are optional.

2) C7 is used only with electronic extension and R7 is used only with mechanical switch

3) Use Connection A when Neutral is not available. Use Connection B when Neutral is available.

4) Connection between Pin 6 and Pin 7 should be broken when EXT is used.

(1)

115V

220V

7237-041597-4

APPLICATION EXAMPLES:

A typical implementation of a lamp dimmer circuit is shown in Fig. 5.
Here the brightness of the lamp is set by touching the Touch Plate .
The functions of different components are as follows:

• The 15V DC supply for the chip is provided by Z, D1, R1, C2, C5.

• R2 and C4 generate the filtered signal for the SYNC input for syn­ chronizing the internal PLL with the line frequency.

• R3 and C7 act as filter circuit for the electronic extension. If exten­ sions are not used, the EXT input (Pin 6) should be tied to VDD
(Pin 7).

• R4, R5, R6 set up the sensitivity of the SENS input. C6 provides
noise filtering.

• C3 is the filter capacitor for the internal PLL.

• R8 provides current limiting and isolation between the chip output
and the triac gate.

• C1 and L are RF filter circuits.
In the case of momentary power failure, the circuit state remains un-

changed for a period up to 1 sec. For longer power interruptions, the
output is shut off.

EXTENSIONS:

All switching and dimming functions can also be implemented by
utilizing the EXT input. This can be done by either a mechanical
switch or the electronic switch in conjunction with a Touch Plate
as shown in Figure 6. When the plate is touched, a logic high lev­el is generated at the EXT input of the IC for both half-cycles of
the line frequency. (See Figure 5)

EXTN

2KΩ,1/4W

IN914

TOUCH PLATE

*R

200KΩ,1/4W

MPS8599

FIGURE 6. ELECTRONIC EXTENSION

P

*R

*R = 2MΩ, 1/4W for 115VAC
*R = 3.6MΩ, 1/4W for 220VAC

(2)

(3)

(4)