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| OPA379AIDBVR Datasheet, PDF (11/29 Pages) Texas Instruments – 1.8V, 2.9mA, 90kHz, Rail-to-Rail I/O PERATIONAL AMPLIFIERS | |||
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OPA379
OPA2379
OPA4379
www.ti.com ................................................................................................................................................... SBOS347D â NOVEMBER 2005 â REVISED MAY 2008
WINDOW COMPARATOR
Figure 24 shows the OPA2379 used as a window
comparator. The threshold limits are set by VH and
VL, with VH > VL. When VIN < VH, the output of A1 is
low. When VIN > VL, the output of A2 is low.
Therefore, both op amp outputs are at 0V as long as
VIN is between VH and VL. This architecture results in
no current flowing through either diode, Q1 in cutoff,
with the base voltage at 0V, and VOUT forced high.
If VIN falls below VL, the output of A2 is high, current
flows through D2, and VOUT is low. Likewise, if VIN
rises above VH, the output of A1 is high, current flows
through D1, and VOUT is low.
The window comparator threshold voltages are set as
follows:
R
VH =
2
R1 + R2
´ VS
(5)
V=
L
R4
R3 + R4
´
V
S
(6)
VS
R1
R2
VS
VH
A1
1/2
OPA2379
D1(2)
RIN
2kW(1)
VIN
R5
10kW
VS
R3
VS
A2
1/2
VL OPA2379
D2(2)
VS
R7
5.1kW
VOUT
Q1(3)
R6
5.1kW
R4
(1) RIN protects A1 and A2 from possible excess current flow.
(2) IN4446 or equivalent diodes.
(3) 2N2222 or equivalent NPN transistor.
Figure 24. OPA2379 as a Window Comparator
Copyright © 2005â2008, Texas Instruments Incorporated
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