LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
鈥?/div>
Input interface to Photo Resistor
鈥?Programmable Duration Selection
鈥?Shunt regulator
鈥?50Hz / 60Hz time base selection
鈥?Relay Driver output
鈥?6.0V 鹵 0.75V operating voltage range (V
DD
- V
SS
)
鈥?LS7217 (DIP), LS7217-S (SOIC)
- See Figure 1 -
APPLICATIONS
Lighting control for low voltage landscape lighting, etc.
PIN ASSIGNMENT
TOP VIEW
8
7
6
5
50Hz / 60Hz Select
50Hz / 60Hz
V
SS
(-V )
Time Select2
LSI
LS7217
2
3
4
DESCRIPTION
FIGURE 1
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-
TIME SELECT Inputs TS1, TS2
(Pins
4, 5)
former and the output drives low-voltage AC loads such as in- The two Select inputs determine the time duration that the
Relay output stays on after the photocell goes low. Both in-
candescent light bulbs.
puts have internal pulldown transistors so that float is logic
zero and connection to V
DD
is logic 1. The Time Select Ta-
PIN DESCRIPTION:
The following describes the operation of the inputs and out- ble is as follows:
puts of the IC.
Time Select1 Time Select2 Time Duration
0
0
4 Hours
V
DD
(Pin
2)
0
1
6 Hours
V
DD
is the supply voltage positive terminal. It is regulated in-
1
0
8 Hours
ternally in the IC. The
internal voltage regulator produces
1
1
Dusk -to-Dawn
6.0V 鹵 0.75V.
A series resistor is required to limit current into
the regulator from 5mA to 10mA over the full transformer op-
Dusk to Dawn duration is determined solely by the photo-
erating voltage range.
cell; i.e., the Relay output is on whenever the photocell
recognizes an ambient dark condition.
V
SS
(Pin
6)
V
SS
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.
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 V
DD
. 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 (鹵 0.5 seconds) continuously
50Hz / 60 Hz Input
(Pin
7)
This input is the clock source for all timing functions. This in- in order to be recognized as a
valid light condition.
A
put accepts a 9VAC to 16VAC input voltage. An external
dark condition
must remain for 1.0 seconds (鹵 0.25 sec-
dropping resistor of 220k Ohms is needed to limit current. onds) continuously in order to be recognized as a
valid
This input has a Schmitt trigger to ensure a clean internal
dark condition.
clock waveform.
RELAY Output
(Pin
1)
This output is configured to drive the base of an external
NPN transistor (see Figure 2).
7217-012608-1
1
2
3
