LSI/CSI UL ® A3800 LS7218 LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405 PROGRAMMABLE LIGHT-ACTIVATED TIMER DESCRIPTION The LS7218 is a Programmable Timer IC designed to turn on a relay at night and turn off the relay at dawn or after a selectable number of hours. Figure 2 shows a typical application schematic. The circuit is powered from a step-down transformer and the output drives low-voltage AC loads such as incandescent light bulbs. PIN DESCRIPTION: The following describes the operation of the inputs and outputs of the IC. Relay OUT 1 V DD (+V ) 2 Photo Resistor 3 Time Select1 4 LS7218 APPLICATIONS Lighting control for low voltage landscape lighting, etc. PIN ASSIGNMENT TOP VIEW LSI FEATURES: • Input interface to Photo Resistor • Programmable Duration Selection • Shunt regulator • 50Hz / 60Hz time base selection • Relay Driver output • 6.0V ± 0.75V operating voltage range (VDD - VSS) • LS7218 (DIP), LS7218-S (SOIC) - See Figure 1 - February 2008 8 50Hz / 60Hz Select 7 50Hz / 60Hz 6 VSS (-V ) 5 Time Select2 FIGURE 1 TIME SELECT Inputs TS1, TS2 (Pins 4, 5) The two Select inputs determine the time duration that the Relay output stays on after the photocell goes low. Both inputs have internal pulldown transistors so that float is logic zero and connection to VDD is logic 1. The Time Select Table is as follows: Time Select1 Time Select2 Time Duration 0 *F 1 Hour VDD (Pin 2) 1 *F 2 Hours VDD is the supply voltage positive terminal. It is regulated in0 0 4 Hours ternally in the IC. The internal voltage regulator produces 0 1 6 Hours 6.0V ± 0.75V. A series resistor is required to limit current into 1 0 8 Hours the regulator from 5mA to 10mA over the full transformer op1 1 Dusk -to-Dawn erating voltage range. *F = Floating VSS (Pin 6) VSS is the supply voltage negative terminal. Dusk to Dawn duration is determined solely by the photocell; i.e., the Relay output is on whenever the photocell rec50Hz / 60 Hz SELECT Input (Pin 8) ognizes an ambient dark condition. A high at this at this input selects the correct timing for 50Hz operation. Floating this input selects the correct timing for PHOTO RESISTOR Input (Pin 3) 60Hz operation. A low at this input places the LS7218 into The photo resistor input has hysteresis for a postiive trip Test Mode where the timeouts are accelerated by a factor of point. The input will work with a photo resistor connected 60. between the input and V DD. The photo resistor provides a low impedance in the presence of ambient light and a high 50Hz / 60 Hz Input (Pin 7) impedance in the presence of ambient darkness. This input is the clock source for all timing functions. This input accepts a 9VAC to 16VAC input voltage. An external The IC is configured so that detection of a light condition dropping resistor of 220k Ohms is needed to limit current. must remain for 6.0 seconds (± 0.5 seconds) continuously in This input has a Schmitt trigger to ensure a clean internal order to be recognized as a valid light condition. A dark clock waveform. condition must remain for 1.0 seconds (± 0.25 seconds) continuously in order to be recognized as a valid dark conRELAY Output (Pin 1) dition. This output is configured to drive the base of an external NPN transistor (see Figure 2). 7218-022608-1 D1 10VAC - 15VAC From Transformer Time Select R1 MOV LDR 50/60Hz Select D2 R2 R4 4 5 3 + C1 - K1 8 2 7 LS7218 6 1 R3 C2 Q1 10VAC -15VAC to Light Bulbs FIGURE 2. TYPICAL LANDSCAPE LIGHTING APPLICATION SCHEMATIC D1 = 1N4004 D2 = 1N4004 C1 = 220uF, 25V C2 = 470pF, 10V Q1 = 2N3904 (Typical) Note: All resistors, 1/4W 7218-012908-2 R1 = 1kΩ R2 = 220kΩ R3 = 25kΩ R4 = Silonex NSL-19M51 (Typical) ABSOLUTE MAXIMUM RATINGS: (All voltages referenced to VSS) SYMBOL VDD VIN TA TSTG DC Supply Voltage Voltage (Any Pin) Operating Temperature Storage Temperature VALUE +8 VSS -0.3 to VDD + 0.3 - 20 to +85 -40 to +150 UNIT V V °C °C DC ELECTRICAL CHARACERISTICS: (TA = 25°C, VDD = 6.0V unless otherwise specified. PARAMETER SYMBOL MIN TYP MAX UNIT TS1, TS2 Low TS1, TS2 High TLO THI 3.0 - 1.4 - V V 50/60 Hz Low 50/60 Hz High VHZL VHZH 4.4 - 2.9 - V V Photo Resistor Inhibit Threshold Enable Threshold VIT VET 3.5 - - 2.9 V V IIH - 24 - mA IOH IOL 4.0 -50 - mA mA Input Current (All inputs high) 50Hz/60Hz Select ] TS1, TS2 ] Output Current Sourcing, VO = 0.7V Sinking, VO = 0.4V - 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. 7218-012908-3