ICL8211 Datasheet, PDF (14/14 Pages) Intersil Corporation – Programmable Voltage Detectors

ICL8211, ICL8212
SPST switches range from push button and slide types to cal-
culator keyboards. A major problem with the use of switches is
the mechanical bounce of the electrical contacts on closure.
Contact bounce times can range from a fraction of a millisec-
ond to several tens of milliseconds depending upon the switch
type. During this contact bounce time the switch may make and
break contact several times. The circuit shown in Figure 37 pro-
vides a rapid charge up of C₁ to close to the positive supply
voltage (V₁) on a switch closure and a corresponding slow dis-
charge of C₁ on a switch break. By proportioning the time con-
stant of R₁ C₁ to approximately the manufacturer’s bounce time
the output as terminal #4 of the ICL8211/8212 will be a single
transition of state per desired switch closure
Low Voltage Power Disconnect (Figure 38)
There are some classes of circuits that require the power
supply to be disconnected if the power supply voltage falls
below a certain value. As an example, the National LM199
precision reference has an on chip heater which malfunc-
tions with supply voltages below 9V causing an excessive
device temperature. The ICL8212 may be used to detect a
power supply voltage of 9V and turn the power supply off to
the LM199 heater section below that voltage.
For further applications, see AN027 “Power Supply Design
using the ICL8211 and ICL8212.”
V+
C₁
INPUT
R₂
R₁
1
8
R₄
2
ICL8212
7
3
6
R₅
A
4
5
1
R₆
8
R₇
2
ICL8212
7
3
6
B
4
5
1
8
ICL8211
2
OR
ICL8212
7
3
#3
6
4
5
R₃
C₂
C₃
TIME CONSTANT R₃C₂ < R₄C₂ ≤ R₇C₃
VARY R₁ FOR OPTION ZERO CROSSING DETECTION
VARY R₄ TO SET DETECTION FREQUENCY
R₆
OUTPUT
INPUT
1.15V
A
1.15V
B
R₄ 100Ω
R₂
R₃
R_{1 C1}
ON TIME #2
OFF
INDETERMINATE
BELOW F_O
ON
F_O
FIGURE 36. FREQUENCY LIMIT DETECTOR
FREQUENCY
1
8
2
ICL8211 ₇
OR
3 ICL8212 6
4
5
V+
500k
R_L
56k
V_O
1
2
ICL8212
3
4
4.7k
8
7
6
3.9k
5
ON
OFF
V-
OUTPUT
REFERENCE
LM199
FIGURE 37. SWITCH BOUNCE FILTER
FIGURE 38. LOW VOLTAGE POWER SUPPLY DISCONNECT
7-174