LS7217 Datasheet, PDF (1/3 Pages) LSI Computer Systems – PROGRAMMABLE LIGHT-ACTIVATED TIMER

LSI/CSI
LS7217
U_{® L}
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 [phone] FAX [phone]
A3800
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
• 6.0V ± 0.75V operating voltage range (VDD - VSS)
• LS7217 (DIP), LS7217-S (SOIC) - See Figure 1 -
APPLICATIONS
Lighting control for low voltage landscape lighting, etc.
PIN ASSIGNMENT
TOP VIEW
Relay OUT 1
V DD (+V ) 2
Photo Resistor 3
Time Select1 4
8 50Hz / 60Hz Select
7 50Hz / 60Hz
6 VSS (-V )
5 _{Time Select2}
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.
VDD (Pin 2)
VDD is the supply voltage positive terminal. It is regulated in-
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.
VSS (Pin 6)
VSS is the supply voltage negative terminal.
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 low 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.
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 in-
puts have internal pulldown transistors so that float is logic
zero and connection to VDD is logic 1. The Time Select Ta-
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
between the input and VDD. The photo resistor provides a
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