touch control continuous dimmer with automatic gain control (agc) features: ? touch or pushbutton control of incandescent lamps. ? touch sensitivity guaranteed to 600pf touch plate capacitance. ? touch operation independent of line plug polarity. ? minimal external components. ? agc loop stabilizes immediately after power-up. ? brightness state is off after ac power applied. ? no change of brightness state if ac power interrupted < 0.5 sec ? advanced cmos design for reliable operating characteristics and low power. ? 50/60 hz line frequency. ? 5v operation (v dd - v ss ). ? LS7540 (dip); LS7540-s (soic) - see figure 1 - applications: ? screw-in and built-in adapter modules for converting table and floor lamps to touch control for continuous dimming. pin assignment top view june 2006 7540-060906-1 lsi/csi l si c o m p u t e r sy s t e m s , i n c . 1 2 3 5 w a l t w h i t m a n r o a d , m e l v i l l e , n y 1 1 7 4 7 ( 6 3 1 ) 2 7 1 - 0 4 0 0 f a x ( 6 3 1 ) 2 7 1 - 0 4 0 5 LS7540 description: the LS7540 is a cmos integrated circuit for controlling the brightness of incandescent lamps with momentary touch. when its touch input is connected to a lamp body, the entire lamp turns into a touch plate. a built-in agc circuit allows for a wide range of lamp sizes to be used, ranging from very small table lamps to very large floor lamps. the brightness is controlled by controlling the conduction angle of a triac in series with the lamp and triggered by the trig/ output. between off and maximum, there are 124 steps of brightness levels, level zero being off and level 124 being maximum. the phase reference of the trig/ sig- nal with respect to the ac line is maintained through the sync input. touch operation the on/off and brightness control of the lamp is made with brief touches of the lamp body as described below: ?in the off state a single touch will turn the lamp to full_on. ?at full-on a single touch will start a dim-cycle causing the brightness to diminish gradually until the lamp turns off. ?during a dim-cycle a single touch will stop the dim-cycle and lock in the brightness present at that time. another touch will re- start the dim-cycle from the present brightness causing the brightness to ramp down towards off again. the start and stop of dim-cycle can be repeated over and over again until the lamp turns off. i nput/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 characteristics. 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. this action alters the state of the trig output as described in the touch operation section of the general de- scription. control i/o (pin 5) an external r-c network connected between this pin and v dd es- tablishes the controlling feedback for the agc loop. ramp input/output (pin 6) the ramp down rate of the brightness in the dimming cycle is regu- lated by a resistor-capacitor (rc) pair connected to the ramp in- put. the ramp rate is equal to 4t rc per step, where t rc = 0.48rc. total ramp down time (t t ) from maximum brightness to off is equal to 496t rc . example: r = 200k w , c = 0.22uf; t rc = 0.48 x (200 x 10 3 ) x (0.22 x 10 -6 ) = 0.02 sec. ramp rate = 4 x t rc = 0.08 sec/step; total ramp time, t t = 496 x t rc = 9.92 sec. v ss (pin 7) supply voltage negative terminal. trig/ output (pin 8) the trig/ output produces a negative pulse every half cycle of the ac line period to turn on a triac in series with the lamp or any other load device. the brightness of the lamp is regulated by regu- lating the conduction angle, (see fig. 2) of the trig/ signal. the conduction angles at maximum brightness (level 124) and mimimum brightness (level 1) are 162?and 50?with 0.91?in- cremental steps. u l a3800 lsi 1 2 3 4 8 7 6 5 LS7540 figure 1 v dd ( +v ) ramp control v ss ( -v ) sync clock touch trig/
absolute maximum ratings: parameter symbol value unit dc supply voltage v dd - v ss +6 v any input voltage v in v ss - 0.3 to v dd + 0.3 v operating temperature t a -20 to +85 ? storage temperature t stg -65 to +150 ? 7540-060906-2 electrical and transient characteristics: ( all voltages referenced to v ss . t a = +25?c unless otherwise specified.) parameter symbol min typ max unit conditions supply voltage v dd +4.5 5.0 +5.5 v - supply current i dd - - 500 ua output off, v dd = +5.0v trig/ sink current i o -50 - - ma v dd = +5.0v vo = v dd - 3v trig/ source current i o +0.1 - - ma v dd = +5.0v vo = v dd - 0.2v trig/ pulse width t w - 105 - ?ec rc = 300k w , 60hz - - 126 - ?ec rc = 360k w , 50hz clock resistor - - 350 - k w 60hz - - 420 - k w 50hz control resistor - - 10 - m w - control capacitor - - 1 - ? - touch plate capacitance - - - 600 pf - touch duration t s 67 - - ms 60hz t s 80 - - ms 50hz conduction angle 50 - 162 deg - incremental steps d - 0.91 - deg - (note 1) ramp resistor r 2 - no limit k w - ramp capacitor c 200 - no limit pf - ramp rc t rc 25 - no limit ? 60hz ramp rc t rc 30 - no limit ? 50hz ramp rate - - 4t rc - sec/step - max to off slew time t t - 496t rc - sec - note 1 : total number of steps = 124.
7540-121605-3 figure 2. trig/ output conduction angle, 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. sync trig/ t w 180 120 60 0 touch max dim cycle off max dim cycle min off dim cycle ts figure 3. touch vs trig/ conduction angle, t t clock 1 2 6 5 3 7 4 clock generator zero cross detect agc touch control brightness control trigger generator sync touch control ramp v dd v ss 8 figure 4. LS7540 block diagram v+ gnd trig/
r1 = 20k w , 1w r2 = 470k w , 1/4w r3 = 1k w , 1/4w r4 = 350k w , 1/4w,1% r5 = 10m w , 1/4w r6 = 100 w , 1/4w r7 = see note 1 c1 = 47?, 16v c2 = 1000pf, 16v c3 = 1000pf, 1kv r1 = 39k w , 2w r2 = 910k w , 1/4w r4 = 420k w , 1/4w, 1% d1 = 1n4005 t1 = q4004l4 (typical triac) or q4004f41 (typical triac) all other values remain the same. c4 = 1000pf, 1kv c5 = 0.03?, 16v (only for figure 5) c6 = 1?, 16v c7 = see note 1 z1 = 5.1v, 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 : see ramp input description for determining values for r7 and c7. 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 c8, 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) 7540-060906-4 ac mains load r1 r3 r4 d1 figure 5. touch lamp application schematic c3 c4 d2 8 7 6 5 v ss ramp cont clock sync v dd touch d3 r2 touch plate (lamp body) c2 t1 g mt2 mt1 z1 c5 r5 c1 + - +v -v LS7540 c6 + - c8* (see note 2) c7 r6 1 2 3 4 trig/ r7 #1
the figure 6 application schematic functions identically to that shown in figure 5 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. 7540-060906-5 ac mains load r1 r3 r4 c1 d1 figure 6. touch lamp application schematic c3 c4 d2 8 7 6 5 v ss ramp cont clock sync v dd touch d3 r2 touch plate (lamp body) c2 t1 g mt2 mt1 z1 r5 + - +v -v LS7540 c6 + - c8* (see note 2) c7 r6 1 2 3 4 trig/ r7 #2
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