U® L LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
TOUCH CONTROL STEP DIMMER LIGHT SWITCH May 2006
WITH AUTOMATIC GAIN CONTROL (AGC)
• 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 (VDD - VSS).
• LS7541 (DIP); LS7541-S (SOIC) - See Figure 1 -
V DD (+V ) 3
7 V SS (-V )
• 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.
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
BRIGHTNESS STEP SEQUENCE
VDD OFF-NIGHT LIGHT- LOW MEDIUM-HIGH MEDIUM-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
60Hz Delay (1)
50Hz Delay (2)
% PWR (3)
(1) With 400kΩ connected between Pin 1 and VDD.
(2) With 470kΩ connected between Pin 1 and VDD.
(3) Percentage of Full Power delivered to a resistive load by the Triac Switch.