THAT1420 Datasheet, PDF (5/8 Pages) List of Unclassifed Manufacturers – Balanced Line Drivers

Rev. 4/24/01
Preliminary Information
Page 5
VCC
C4
100n
In
6
7
4
Vcc
In ^Sens+
8
Out+
3 _{GnVd5eSe2ensO-UTu1HtA1-T1420}
C5
100n
VEE
VCC
C6
100n
2
7
In-
Vcc
6 ^Out
Out
Ref
3 Vee
In+
1 _U2
4
THAT1243 or equiv.
C7
VEE _100n
Figure 4. Basic THAT 1420 applications circuit
Applications
Circuit implementations using the THAT
1420/1430 are relatively straightforward. A quiet,
solid ground reference, stiff voltage supplies, and ad-
equate supply bypassing are all that is required to
achieve excellent performance out of both ICs. Both
devices are stable into any capacitive load, and the
maximum capacitance is limited only by slew rate
and frequency response considerations.
For the purposes of the frequency response calcu-
lation, the line driver’s 50W sense resistors can be
lumped into a single 100W resistor. The correct ca-
ble capacitance to use is the sum of the
inter-conductor capacitance and the two conduc-
tor-to-shield capacitances. Unfortunately, some man-
ufacturers only specify the inter-conductor
capacitance and the capacitance of one conductor to
the other while connected to the shield, and some ex-
traction may be required.
As an example, one manufacturer supplies a
shielded, twisted pair with 30pF/ft of inter-conductor
capacitance and 25pF/ft of conductor to shield capac-
4. Copyright ã 1991 Rane Corporation
itance. The corner frequency of the THAT 1420/1430
driving 500 ft of this cable will be
f_C
=
1
2´p ´100W´500 (30 ^pF
ft^{+ 25 pF}
ft^{+ 25 pF}
ft⁾
» 40kHz
One must also consider the slew rate limitations
posed by excessive cable and other capacitances. We
know that
i
=
C
dV
dt
and that
dV
dt
=
V_Peak
´ 2p
´
f
Rane Corporation has published a document titled
RaneNote 126⁴, which specifies some of the require-
ments for a balanced line driver, including a)
stablility into reactive loads, b) output voltage swing
of at least ±11 volts peak (+20dBu), and c) reliabil-
ity. This document also suggests a reasonable rule
by which to calculate the output current require-
ments at 20kHz. The author concludes that the ac-
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