LSI/CSI
UL
®
LS7541
(631) 271-0400 FAX (631) 271-0405
March 2007
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
A3800
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.
5V Operation (V
DD
- V
SS
).
LS7541 (DIP); LS7541-S (SOIC) -
See Figure 1 -
PIN ASSIGNMENT
TOP VIEW
CLOCK
SYNC
V
DD
(+V )
TOUCH
1
LSI
8
TRIG
V
SS
(-V )
2
7
LS7541
3
6
MODE
CONTROL
• 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.
• Wall Switch Step Dimmers
APPLICATIONS:
4
5
FIGURE 1
DESCRIPTION:
The LS7541 is a CMOS integrated circuit which provides 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
FLOAT
V
DD
Vss
BRIGHTNESS STEP SEQUENCE
OFF-NIGHT LIGHT-MEDIUM-MAXIMUM-OFF
OFF-NIGHT LIGHT- LOW MEDIUM-HIGH MEDIUM-MAXIMUM-OFF
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.
TABLE 2. BRIGHTNESS POWER LEVELS
Brightness
Night Light
Low Medium
Medium
High Medium
Maximum
60Hz Delay
(1)
6.0 ms
4.8 ms
4.0 ms
3.2 ms
0.85 ms
50Hz Delay
(2)
7.2 ms
5.7 ms
4.8 ms
3.8 ms
1.0 ms
% PWR
(3)
12
35
53
72
99
(2) With 470kΩ connected between Pin 1 and V
DD
.
(1) With 400kΩ connected between Pin 1 and V
DD
.
(3) Percentage of Full Power delivered to a resistive load by the Triac Switch.
7541-032307-1
FIGURE 2. OUTPUT DELAY (Td)
SYNC (Pin 2)
TRIG (Pin 8)
Td
Td
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)
50 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
Brightness Step Sequence (See Table 1).
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)
ABSOLUTE MAXIMUM RATINGS:
PARAMETER
DC supply voltage
Any input voltage
Operating temperature
Storage temperature
SYMBOL
V
DD -
V
SS
V
IN
T
A
T
STG
VALUE
+7
V
SS
- 0.5 to V
DD
+ 0.5
-20 to +85
-65 to +150
UNIT
V
V
°C
°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.
7541-072805-2
ELECTRICAL CHARACTERISTICS:
(All voltages referenced to Vss. T
A
= +25˚C unless otherwise specified.)
PARAMETER
Supply Voltage
Supply Current
TRIG
Sink Current
Vo = V
DD
- 3V
TRIG
Source Current
Vo = V
DD
- 0.2V
TRIG
Pulse Width
TRIG
Pulse Delay
(Medium Brightness)
CLOCK
Resistor
CONTROL
Resistor
Capacitor
Touch Plate Capacitance
SYMBOL
V
DD
I
DD
I
O
I
O
T
W
-
Td
R
C
-
-
-
C
L
MIN
+4.5
-
-50
+0.1
-
-
-
-
-
-
-
-
-
TYP
-
-
-
-
100
115
4.0
4.8
400
470
10
1
-
MAX
+5.5
1.0
-
-
-
-
-
-
-
-
-
-
600
UNIT
V
mA
mA
mA
µs
µs
ms
ms
kΩ
kΩ
MΩ
µF
pF
CONDITIONS
-
Output off,
V
DD
= +5.0V
V
DD
= +5.0V
V
DD
= +5.0V
R
C
= 400kΩ, 60Hz
R
C
= 470kΩ, 50Hz
Rc = 400kΩ, 60Hz
Rc = 470kΩ, 50Hz
60Hz
50Hz
-
-
-
MODE
6
ZERO-CROSS
DETECTOR
SYNC
2
CLOCK
1
OSCILLATOR
COUNTER
DECODER
OUTPUT
DRIVER
8
TRIG
TOUCH
4
AGC CIRCUIT
STEPPER
CONTROL
5
V
DD
V
SS
3
7
+V
-V
FIGURE 3
LS7541 BLOCK DIAGRAM
7541-072805-3
FIGURE 4. TOUCH LAMP APPLICATION SCHEMATIC
+V
R1
D1
LOAD
AC
MAINS
C1
Z1
+
-
MT2
MT1
T1
G
R6
R5
+
-
C6
-V
C2
C5
8
TRIG
SEE
NOTE 1
7
V
SS
6
MODE
LS7541
5
CONT
C7*
(SEE NOTE 2)
CLOCK SYNC V
DD
TOUCH
R2
1
R4
2
3
D2
4
D3
TOUCH PLATE
(LAMP BODY)
R3
C3
C4
R1 = 20kΩ, 1W
R2 = 470kΩ, 1/4W
R3 = 1kΩ, 1/4W
(1)
R4 = 400kΩ, 1/4W, 1%
R5 = 10MΩ, 1/4W
R6 = 100Ω, 1/4W
C1 = 47µF, 10V
C2 = 1000pF, 10V
C3 = 1000pF, 1kV
115VAC APPLICATION
C4 = 1000pF, 1kV
C5 = 0.03µF, 10V
C6 = 1µF, 10V
Z1 = 5.1V, 1/4W Zener
D1 = 1N4004
D2 = 1N4148
D3 = 1N4148
T1 = Q2004L4 (Typical Triac)
or Q2004F41 (Typical Triac)
220VAC APPLICATION
R1 = 39kΩ, 2W
R2 = 910kΩ, 1/4W
(1
)
R4 = 470kΩ, 1/4W, 1%
D1 = 1N4005
T1 = Q4004L4 (Typical Triac)
or Q4004F41 (Typical Triac)
All other values remain the same.
(1)
Resistor should be placed adjacent to Pin 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 1kΩ to 5.1kΩ and add C7, a 0.1µF 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)
7541-011706-4
FIGURE 5. TOUCH LAMP APPLICATION SCHEMATIC
-V
R1
D1
LOAD
-
AC
MAINS
Z1
C1
MT2
MT1
T1
G
R6
SEE
NOTE 1
+
+
+V
R5
-
C6
C2
8
TRIG
7
6
LS7541
5
CONT
C7*
(SEE
NOTE 2
)
V
SS
MODE
CLOCK SYNC
V
DD
TOUCH
R2
1
R4
2
3
D2
44
D3
TOUCH PLATE
(LAMP BODY)
C3
C4
R3
The Figure 5 Application Schematic functions identically to that shown in Figure 4 with one less component.
Referencing Triac T1 to the +V power supply of the IC eliminates the need to AC couple the TRIAC pulse
to the Triac Gate thereby eliminating component C5.
FIGURE 6. PUSHBUTTON APPLICATION SCHEMATIC
-V
R1
D1
LOAD
-
AC
MAINS
Z1
C1
MT2
MT1
T1
G
R6
SEE
NOTE 1
+
+
+V
R5
-
C6
C2
8
TRIG
7
V
SS
6
LS7541
5
MODE CONT
CLOCK SYNC
V
DD
TOUCH
R2
1
R4
2
3
4
C3
S1
Using the Figure 5 schematic as an example, components R3, C4, C7, D1 and D2 are eliminated and
Pushbutton Switch, S1, is connected from one end of C3 to V
SS.
Each depression of S1 causes the
Brightness Level to change in the same way as a Touch does in Figure 5.
C3 is 1000pf, 10V capacitor.
7541-022807-5
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