PROGRAMMABLE LIGHT-ACTIVATED TIMER

January 2008

FEATURES:

• Input interface to Photo Resistor

• Programmable Duration Selection

• Shunt regulator

• 50Hz / 60Hz time base selection

• Relay Driver output

• LS7217 (DIP), LS7217-S (SOIC)

- See Figure 1 -

APPLICATIONS

Lighting control for low voltage landscape lighting, etc.

DESCRIPTION

The LS7217 is a Programmable Timer IC designed to turn on

a relay at night and turn off the relay at dawn or after a select-

able number of hours. Figure 2 shows a typical application

schematic. The circuit is powered from a step-down trans-

former and the output drives low-voltage AC loads such as in-

candescent light bulbs.

PIN DESCRIPTION:

The following describes the operation of the inputs and out-

puts of the IC.

ternally in the IC. The

internal voltage regulator produces

6.0V ± 0.75V. A series resistor is required to limit current into

the regulator from 5mA to 10mA over the full transformer op-

erating voltage range.

50Hz / 60 Hz SELECT Input (Pin 8)

A

high at this at this input selects the correct timing for 50Hz

operation.

Floating this input selects the correct timing for

60Hz operation. A l

ow at this input places the LS7217 into

Test Mode where the timeouts are accelerated by a factor of

60.

50Hz / 60 Hz Input (Pin 7)

This input is the clock source for all timing functions. This in-

put accepts a 9VAC to 16VAC input voltage. An external

dropping resistor of 220k Ohms is needed to limit current.

This input has a Schmitt trigger to ensure a clean internal

clock waveform.

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 in-

puts have internal pulldown transistors so that float is logic

ble is as follows:

Time Select1 Time Select2 Time Duration

0

0

4 Hours

0

1

6 Hours

1

0

8 Hours

1

1

Dusk -to-Dawn

Dusk to Dawn duration is determined solely by the photo-

cell; i.e., the Relay output is on whenever the photocell

recognizes an ambient dark condition.

PHOTO RESISTOR Input (Pin 3)

The photo resistor input has hysteresis for a postiive trip

point. The input will work with a photo resistor connected

low impedance in the presence of ambient light and a high

impedance in the presence of ambient darkness.

The IC is configured so that detection of a

light condition

must remain for 6.0 seconds (± 0.5 seconds) continuously

in order to be recognized as a

valid light condition. A

dark condition must remain for 1.0 seconds (± 0.25 sec-

onds) continuously in order to be recognized as a

valid

dark condition.

RELAY Output (Pin 1)

This output is configured to drive the base of an external

NPN transistor (see Figure 2).

7217-012608-1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

LS7217

UL

®

A3800

1

2

3

4

8

7

6

5

50Hz / 60Hz

Time Select1

Time Select2

Relay OUT

50Hz / 60Hz Select

Photo Resistor

FIGURE 1

PIN ASSIGNMENT

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