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 december 2002 7538/39-120202-1 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 w connected between pin 1 and v dd . (2) with 360k w 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 u l 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) 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 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 ? storage temperature t stg -65 to +150 ? 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. 7538/39-041597-2
electrical characteristics: ( all voltages referenced to vss. t a = +25?c 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 - v trig source current i o +0.1 - - ma v dd = +8.0v vo = v dd - 0.2v trig pulse width t w - 90 - ? r c = 300k w , 60hz - - 110 - ? r c = 360k w , 50hz trig pulse delay td - 4.0 - ms rc = 300k w , 60hz (medium brightness) - 4.8 - ms rc = 360k w , 50hz clock resistor r c - 300 - k w 60hz - - 360 - k w 50hz control resistor - - 10 - m w - capacitor - - 1 - ? - touch plate capacitance c l - - 600 pf - figure 3 ls7538/ls7539 block diagram mode sync clock touch control zero-cross detector oscillator agc circuit counter stepper decoder output driver trig 7 v ss v dd 3 5 4 1 2 6 +v -v 8 7538/39-041197-3
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 plate (lamp body) c2 (see note 1) t1 g mt2 mt1 z1 c5 c6 r5 + - +v -v ls7538 + - c7* (see note 2) r1 = 20k w , 1w r2 = 470k w , 1/4w r3 = 1k w , 1/4w r4 = 300k w , 1/4w, 1% r5 = 10m w , 1/4w c1 = 47?, 16v c2 = 1000pf, 16v c3 = 1000pf, 1kv r1 = 39k w , 2w r2 = 910k w , 1/4w r4 = 360k w , 1/4w, 1% d1 = 1n4005 t1 = q4004l4 (typical triac) or q4004f41 (typical triac) all other values remain the same. c4 = 1000pf, 1kv c5 = .03?, 16v c6 = 1?, 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 w to 5.1k w and add c7, a 0.1? 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) 7538/39-091100-4
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