LT1794ISW View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LT1794ISW Datasheet PDF : 20 Pages
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LT1794
APPLICATIO S I FOR ATIO
SHDN
5I 2k
I
2I
2I
TO
START-UP
CIRCUITRY
SHDNREF
1k
IBIAS
TO AMPLIFIERS
BIAS CIRCUITRY
1794 F01
IBIAS
=
2
5
ISHDN
=
ISHDNREF
ISUPPLY PER AMPLIFIER (mA) = 64 • IBIAS
Figure 1. Internal Current Biasing Circuitry
outputs are in a high impedance state. Part to part varia-
tions however, will cause inconsistent control of the qui-
escent current if direct voltage drive of the SHDN pin is used.
Using a single external resistor, RBIAS, connected in one of
two ways provides a much more predictable control of the
quiescent supply current. Figure 2 illustrates the effect on
supply current per amplifier with RBIAS connected be-
tween the SHDN pin and the 12V V+ supply of the LT1794
and the approximate design equations. Figure 3 illustrates
the same control with RBIAS connected between the
SHDNREF pin and ground while the SHDN pin is tied to V+.
Either approach is equally effective.
30
VS = ±12V
25
20
15
10
5
0
7
10
V+ = 12V
RBIAS
SHDN
IS
PER
AMPLIFIER
(mA)
≈
V+ – 1.2V
RBIAS + 2k
•
25.6
RBIAS
=
IS
PER
V+ – 1.2V
AMPLIFIER
(mA)
•
25.6
–
2k
SHDNREF
40
70
100
130
160
RBIAS (kΩ)
Figure 2. RBIAS to V+ Current Control
190
1794 F02
45
VS = ±12V
40
35
30
V+ = 12V
SHDN
IS
PER
AMPLIFIER
(mA)
≈
V+ – 1.2V
RBIAS + 5k
•
64
25
20
RBIAS
=
IS
PER
V+ – 1.2V
AMPLIFIER
(mA)
•
64
–
5k
SHDNREF
15
RBIAS
10
5
0
4
7
10 30 50 70 90 100 130 150 170 190 210 230 250 270 290
RBIAS (kΩ)
1794 F03
Figure 3. RBIAS to Ground Current Control
8
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