TOUCH CONTROL STEP DIMMER LIGHT SWITCH
WITH AUTOMATIC GAIN CONTROL (AGC)
FEATURES:
Touch Sensitivity guaranteed to 600pF Touch Plate Capacitance.
Touch Operation independent of line plug polarity.
Pin selection of three available Brightness Step Sequences.
Minimal external components.
AGC Loop stabilizes immediately after Power-Up.
Brightness state is Off after AC power applied.
Brightness state is unchanged if AC power interrupted for < 0.5 sec.
Advanced CMOS design for reliable operating characteristics and low power.
50/60 Hz Line Frequency.
+6V to +9.5V Operation (V
DD
- V
SS
).
LS7538, LS7539 (DIP); LS7538-S, LS7539-S (SOIC) - See Figure 1
APPLICATIONS:
Screw-in and built-in adapter modules for converting table and floor lamps
to touch control for step dimming.
On-Off touch control of under-cabinet fluorescent lamps (LS7539 only).
DESCRIPTION:
The LS7538 and LS7539 are CMOS integrated circuits which provide trigger pulses for triac phase control of incandescent lamps.
The circuits are designed to operate with a wide variety of lamp sizes ranging from small table lamps to large floor lamps.
The AGC Loop automatically adjusts Touch Sensitivity to be independent of lamp size.
There are 3 different Brightness Step Sequences for each version of the IC which can be selected by the Three-State
MODE pin as shown in Table 1.
TABLE 1. BRIGHTNESS STEP MODES
MODE PIN BRIGHTNESS STEP SEQUENCE
FLOAT
OFF-NIGHT LIGHT-MEDIUM-MAXIMUM-OFF
V
DD
OFF-NIGHT LIGHT- LOW MEDIUM-HIGH MEDIUM-MAXIMUM-OFF
Vss (LS7538)
OFF-MAXIMUM-MEDIUM-NIGHT LIGHT-OFF
(LS7539)
OFF-MAXIMUM-OFF
The lamp brightness is made to vary by changing the delay of the TRIG pulse to the triac from the zero-crossing of the
SYNC input. The delays are shown in Table 2 for 50Hz and 60Hz operation along with Delivered Power as a percentage
of Full Power. Figure 2 illustrates the delay.
PIN ASSIGNMENT
TOP VIEW
LSI
1
2
3
4
8
7
6
5
LS7538/7539
FIGURE 1
TRIG
V
DD
(+V
)
MODE
CONTROL
V
SS
(-V)
SYNC
CLOCK
TOUCH
January 2003
7538-012703-1
TABLE 2. BRIGHTNESS POWER LEVELS
Brightness 60Hz Delay (1) 50Hz Delay (2) % PWR (3)
Night Light
6.0 ms
7.2 ms
12
Low Medium
4.8 ms
5.7 ms
35
Medium
4.0 ms
4.8 ms
53
High Medium
3.2 ms
3.8 ms
72
Maximum
0.85 ms
1.0 ms
99
(1) With 300k
connected between Pin 1 and V
DD
. (2) With 360k
connected between Pin 1 and V
DD
.
(3) Percentage of Full Power delivered to a resistive load by the Triac Switch.
LSI/CSI
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
LS7538-LS7539
UL
A3800
INPUT/OUTPUT DESCRIPTION:
CLOCK Input (Pin 1)
An external resistor connected between this input and
V
DD
, along 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 CHAR-
ACTERISTICS. The resistor value determines the Bright-
ness Levels produced. (See Table 2)
SYNC Input (Pin 2)
50Hz or 60Hz AC input for zero crossing detection.
V
DD
(Pin 3)
Supply voltage positive terminal.
TOUCH Input (Pin 4)
Input for sensing that a touch has been made on a lamp
surface or other touch plate.
CONTROL I/O (Pin 5)
An external R-C network connected between this pin
and V
DD
establishes the controlling feedback for the
AGC Loop.
MODE Input (Pin 6)
A three-state input used to select the desired Bright-
ness Step Sequence (See Table 1). The MODE Input
may be changed during operation.
V
SS
(Pin 7)
Supply voltage negative terminal.
TRIG (Pin 8)
The TRIG output produces a negative going pulse eve-
ry half-cycle of the SYNC input to trigger the triac. The
delay, Td, of the pulse with respect to the SYNC signal
determines the Brightness Level produced.
(See Table 2 & Figure 2)
SYNC (Pin 2)
FIGURE 2. OUTPUT DELAY (Td)
Td
Td
TRIG(Pin 8)
ABSOLUTE MAXIMUM RATINGS:
PARAMETER
SYMBOL
VALUE
UNIT
DC supply voltage
V
DD -
V
SS
+11
V
Any input voltage
V
IN
V
SS
- 0.5 to V
DD
+ 0.5
V
Operating temperature
T
A
-20 to +85
C
Storage temperature T
STG
-65 to +150
C
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.
7538-012703-2
ELECTRICAL CHARACTERISTICS:
( All voltages referenced to Vss. T
A
= +25C unless otherwise specified.)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNIT
CONDITIONS
Supply Voltage
V
DD
+6
-
+9.5
V
-
Supply Current
I
DD
-
-
1.5
mA
Output off,
V
DD
= +8.0V
TRIG Sink Current
I
O
-50
-
-
mA
V
DD
= +8.0V
Vo = V
DD
- 3V
TRIG Source Current
I
O
+0.1
-
-
mA
V
DD
= +8.0V
Vo = V
DD
- 0.2V
TRIG Pulse Width
T
W
-
90
-
s
R
C
= 300k
, 60Hz
-
-
110
-
s
R
C
= 360k
, 50Hz
TRIG Pulse Delay
Td
-
4.0
-
ms
Rc = 300k
, 60Hz
(Medium Brightness)
-
4.8
-
ms
Rc = 360k
, 50Hz
CLOCK Resistor
R
C
-
300
-
k
60Hz
-
-
360
-
k
50Hz
CONTROL Resistor
-
-
10
-
M
-
Capacitor
-
-
1
-
F
-
Touch Plate Capacitance C
L
-
-
600
pF
-
FIGURE 3
LS7538/LS7539 BLOCK DIAGRAM
MODE
SYNC
CLOCK
TOUCH
C O N T R O L
Z E R O - C R O S S
D E T E C T O R
OSCILLATOR
AGC CIRCUIT
C O U N T E R
S T E P P E R
D E C O D E R
O U T P U T
DRIVER
TRIG
7
V
SS
V
DD
3
5
4
1
2
6
+V
-V
8
7538-012703-3
AC
MAINS
LOAD
C4
R1
R3
R4
C1
D1
FIGURE 4. TOUCH LAMP APPLICATION SCHEMATIC
C3
D2
8
7
6
5
4
3
2
1
TRIG
V
SS
MODE CONT
CLOCK SYNC V
DD
TOUCH
D3
R2
TOUCH
P L A T E
(LAMP BODY)
C2
( S E E N O T E 1 )
T1
G
MT2
MT1
Z1
C5
C6
R5
+
-
+V
-V
L S 7 5 3 8
+
-
C7*
( S E E N O T E 2 )
R1 = 20k
, 1W
R2 = 470k
, 1/4W
R3 = 1k
, 1/4W
R4 = 300k
, 1/4W, 1%
R5 = 10M
, 1/4W
C1 = 47F, 16V
C2 = 1000pF, 16V
C3 = 1000pF, 1kV
R1 = 39k
, 2W
R2 = 910k
, 1/4W
R4 = 360k
, 1/4W, 1%
D1 = 1N4005
T1 = Q4004L4 (Typical Triac)
or Q4004F41 (Typical Triac)
All other values remain the same.
C4 = 1000pF, 1kV
C5 = 0.03F, 16V
C6 = 1F, 16V
Z1 = 8.2V, 1/4W Zener
D1 = 1N4004
D2 = 1N4148
D3 = 1N4148
T1 = Q2004L4 (Typical Triac)
or Q2004F41 (Typical Triac)
220VAC APPLICATION
115VAC APPLICATION
(1) Resistor should be placed adjacent to Pin 1.
(1)
(1
)
NOTE 1: Connect MODE (Pin 6) for desired Brightness Step Sequence (See Table 1).
NOTE 2: A good PCB layout using through-hole components will provide protection for ESD introduced at the Touch Plate in the range
of 25kV. Using surface mount components and/or a poor PCB layout can reduce the ESD protection. The OEM can increase
the ESD protection provided by the product with any combination of the following steps:
Step 1: The most effective and least costly way to increase ESD protection is to create a spark gap around the Touch Plate input on
the PCB. This will increase ESD protection on a good PCB layout to abut 35kV. The gap should be made with a split metal ring
with each side of the metal ring connected back to opposite sides of the AC line. This ensures that a path for the spark back to
house ground through AC Neutral exists independent of line plug polarity. The split ring and the center conduction plate should
be constructed so that the spacing between them conforms to UL requirements. The spark gap will absorb most of the ESD
leaving a remnant of about 10kV for the rest of the circuit to absorb.
Step 2: Increase R3 from 1k
to 5.1k
and add C7, a 0.1F capacitor, between V
DD
and Vss.
(A minimal loss in touch sensitivity may be experienced.)
Step 3: Replace diodes D2 and D3 (1N4148) with Schottky diodes (1N5819 or similar)
7538-012703-4
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