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ICL7665S Datasheet(PDF) 7 Page - Intersil Corporation

Part No. ICL7665S
Description  CMOS Micropower Over/Under Voltage Detector
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
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ICL7665S Datasheet(HTML) 7 Page - Intersil Corporation

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7
FN3182.8
April 5, 2006
Detailed Description
As shown in the Functional Diagram, the ICL7665S consists
of two comparators which compare input voltages on the
SET1 and SET2 terminals to an internal 1.3V bandgap
reference. The outputs from the two comparators drive
open-drain N-channel transistors for OUT1 and OUT2, and
open-drain P-channel transistors for HYST1 and HYST2
outputs. Each section, the Undervoltage Detector and the
Overvoltage Detector, is independent of the other, although
both use the internal 1.3V reference. The offset voltages of
the two comparators will normally be unequal so VSET1 will
generally not quite equal VSET2.
The input impedance of the SET1 and SET2 pins are
extremely high, and for most practical applications can be
ignored. The four outputs are open-drain MOS transistors,
and when ON behave as low resistance switches to their
respective supply rails. This minimizes errors in setting up
the hysteresis, and maximizes the output flexibility. The
operating currents of the bandgap reference and the
comparators are around 100nA each.
Precautions
Junction isolated CMOS devices like the ICL7665S have an
inherent SCR or 4-layer PNPN structure distributed
throughout the die. Under certain circumstances, this can be
triggered into a potentially destructive high current mode.
This latchup can be triggered by forward-biasing an input or
output with respect to the power supply, or by applying
excessive supply voltages. In very low current analog
circuits, such as the ICL7665S, this SCR can also be
triggered by applying the input power supply extremely
rapidly (“instantaneously”), e.g., through a low impedance
battery and an ON/OFF switch with short lead lengths. The
rate-of-rise of the supply voltage can exceed 100V/
µs in
such a circuit. A low impedance capacitor (e.g., 0.05
µF disc
ceramic) between the V+ and GND pins of the ICL7665S
can be used to reduce the rate-of-rise of the supply voltage
in battery applications. In line operated systems, the rate-of-
rise of the supply is limited by other considerations, and is
normally not a problem.
If the SET voltages must be applied before the supply
voltage V+, the input current should be limited to less than
0.5mA by appropriate external resistors, usually required for
voltage setting anyway. A similar precaution should be taken
with the outputs if it is likely that they will be driven by other
circuits to levels outside the supplies at any time.
Simple Threshold Detector
Figure 9 shows the simplest connection of the ICL7665S for
threshold detection. From the graph 9B, it can be seen that
at low input voltage OUT1 is OFF, or high, while OUT2 is
ON, or low. As the input rises (e.g., at power-on) toward
VNOM (usually the eventual operating voltage), OUT2 goes
high on reaching VTR2. If the voltage rises above VNOM as
much as VTR1, OUT1 goes low. The equation giving VSET1
and VSET2 are from Figure 9A:
Since the voltage to trip each comparator is nominally 1.3V,
the value VIN for each trip point can be found from
and
1
2
3
4
8
7
6
5
OUT1
HYST1
SET1
GND
V+
OUT2
SET2
HYST2
INPUT
HYST2
OUT2
OUT1
V+
20
k
12
pF
12
pF
12
pF
12
pF
20
k
4.7k
HYST1
4.7
k
1.0V
1.6V
FIGURE 7. TEST CIRCUITS
VSET1,
VSET2
tSO1D
tO1F
tSO1D
tO1R
tSH1D
tH1R
tSH1D
tH1F
tSO2D
tO2R
tSO2D
tO2F
tSH2D
tH2R
tSH2D
tH2F
1.6V
1.0V
V+
GND
GND
GND
GND
(5V)
V+
(5V)
V+
(5V)
V+
(5V)
INPUT
OUT1
HYST1
OUT2
HYST2
FIGURE 8. SWITCHING WAVEFORMS
VSET1
VIN
R11
R11 R21
+
()
--------------------------------
=
VSET2
VIN
R12
R12 R22
+
()
--------------------------------
=
VTR1
VSET1
R11 R21
+
()
R11
----------------------------------
1.3
R11 R21
+
()
R11
---------------------------------- for detector 1
=
=
VTR2
VSET2
R12 R22
+
()
R12
----------------------------------
1.3
R12 R22
+
()
R12
---------------------------------- for detector 2
=
=
ICL7665S


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