LSI/CSI
UL
®
LS7338
(631) 271-0400 FAX (631) 271-0405
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
A3800
DELAYED-OFF LIGHT SWITCH
WITH PROGRAMMABLE ON-TIMER
FEATURES:
• Phase-Lock Loop Synchronization allows use in
Wall Switch Applications.
• Operation automatically sequences from Timed-On to
Delayed-Off to Off.
• On-Timer programmable with external R-C.
• Transition from Timed-On to Delayed Off indicated by
31% drop in Delivered Power.
• Delayed-Off period denoted by Dim-to-Off operation.
(See Note 1)
• Control input initiates Operating Sequence and can override
Automatic Sequencing.
• 50/60Hz Line Frequency.
• +12V to +18V Operation (V
SS
- V
DD
).
• LS7338 (DIP); LS7338-S (SOIC) - See Figure 1
NOTE 1:
Dim-to-Off time is Mask Programmable. The standard
IC is fixed at 209 seconds for 60Hz. Dim-to-Off time can be pro-
grammed within a range of 6.5 to 836 seconds.
APPLICATIONS:
• WALL SWITCH for incandescent lighting in garage, corridor,
staircase, child’s bedroom, teenage study area.
• IN-LINE SWITCH for table lamps.
DESCRIPTION:
The LS7338 is a monolithic MOS integrated circuit designed to turn a
triac On and Off in a Power Switch for Incandescent Lighting. Ac-
tivation of SENSE or SLAVE inputs turns the triac On and starts a
timer. The triac remains On for the duration of the Timer which is
controlled by an external R-C connected to the OSCILLATOR input.
When Time-out occurs, the power delivered by the triac is stepped
down by 31% and then slowly reduced to Off over a fixed period of
time.
In a typical application (Figure 5), the output of the LS7338 drives
the gate of a triac in series with the load.
There are three states through which the LS7338 can be stepped.
The states and their corresponding operating mode, phase angles
and delivered power levels are shown in Table 1.
(See Figures 2 and 3)
OPERATING MODE
PHASE ANGLE, ø
% LOAD POWER
(1)
TABLE 1
STATE 0
STATE 1
OFF
No Output
0
Timed-On
159˚
99
STATE 2
Delayed -Off
107˚ to 41˚
68 to 7
PIN ASSIGNMENT - TOP VIEW
June 2001
SENSE
1
8
SYNC
LSI
SLAVE
2
7
CAP
LS7338
V
DD
(-V)
3
6
OSC
TRIG
4
5
V
SS
(+V)
FIGURE 1
OPERATING DESCRIPTION:
Upon power up, internal power-on-reset starts the LS7338 in
STATE 0. When the SENSE input transitions to logic 0, or the
SLAVE input transitions to logic 1, the IC steps to STATE 1.
When implemented as shown in the application example (Fig-
ure 5), this is accomplished by touching the appropriate Sensor
Plate. Subsequent similar transitions at SENSE or SLAVE in-
puts cause the LS7338 to step through the sequence:
STATE 0 --> STATE 1 --> STATE 2 --> STATE 0, etc.
STATE 1 and STATE 2 are quasi-stable states. If left in STATE
1, after a time-out period determined by the frequency set at
the OSC input (See I/O Description, Pin 6), the IC automatically
steps to STATE 2. (If the OSC input is deactivated, STATE 1
becomes stable and its OPERATING MODE is denoted as On).
When the IC steps from STATE 1 to STATE 2, the output
phase angle ø changes from 159˚ to 107˚. This corresponds to
a delivered power reduction of 31%, which causes a reduction
of lamp brightness. This brightness change provides the user
with a positive indication that the transition from STATE 1 to
STATE 2 has occurred. The Time-out period for STATE 2 is
fixed at 209 seconds for 60Hz operation. (See Note 1.)
T
D1
= STATE 1 Time-out period.
T
D2
= STATE 2 Time-out period.
During the STATE 2 Time-out, the TRIG phase angle ø (See
Figure 2) is ramped down from 107˚ to 41˚ in decrements of
1.4˚. When
ø
reaches 41˚, the IC automatically steps to STATE
0, shutting the TRIG and lamp Off.
The slow Dim-to-Off in STATE 2 gives the user a continuing re-
minder that Delayed-Off is operating and provides the time and
light with which to leave the area or to recycle the Light Switch.
A new operating sequence from STATE 0 can be started only by
transitions at the SENSE and SLAVE inputs.
(1)
The percentage of full power delivered to a resistive load by the
triac switch.
7338-062001-1
LSI [ LSI COMPUTER SYSTEMS ]
