LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
TOUCH CONTROL STEP DIMMER LIGHT SWITCH
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.
• +6V to +9.5V Operation (VDD-VSS).
• LS7538, LS7539 (DIP); LS7538-S, LS7539-S (SOIC) - See Figure 1
• 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).
7 V SS(-V)
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
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 300kΩ connected between Pin 1 and VDD.
(2) With 360kΩ connected between Pin 1 and VDD.
(3) Percentage of Full Power delivered to a resistive load by the Triac Switch.