THAT1420 Datasheet, PDF (7/8 Pages) List of Unclassifed Manufacturers – Balanced Line Drivers

Rev. 4/24/01
Preliminary Information
Page 7
VCC
C1
C4
100n
10u
6
In
4 _{InVcScens7O+ut8+}
3 _{GnVdeeSensO-utU-1 1}
2 ^THAT1420
5
C2
C5
10u
100n
VEE
D3
SB160
D4
SB160
D5
SB160
D6
SB160
L1
Ferrite Bead
L2
Ferrite Bead
Out Hi
C8
100p
C3
100p
Out Lo
Figure 6. 1420 with output common mode offset protection, RFI protection, and surge protection
tors whose purpose is to redirect this RF energy to
the chassis before it can circulate and effectively form
a single loop transformer that magnetically couples
RF into the remainder of the circuit. Ferrite beads
are also included to ensure that RFI current is di-
rected to the chassis and not through the relatively
low impedance (at RF frequencies) output of the
THAT 1420/1430. The devices will have no effect on
the gain error of these line drivers at audio frequen-
cies.
While both of these chips have diode protection to
the rails, this protection might not be adequate for
some conditions seen in the field. The most obvious
problem that one might foresee would be having the
line driver’s output plugged directly into a micro-
phone preamplifier input that has +48V phantom
power applied. This situation can result in surge
currents of several amps, which can cause open cir-
cuits in the metal traces or failure of the protection
diodes on the IC.
This circuit uses a discrete diode bridge com-
posed of SB160’s to clamp potentially damaging
surges to the IC’s supply rails.
Closing thoughts
The integrated balanced line driver is one of those
highly useful, cost-effective functional blocks that can
provide significant improvement over discrete de-
signs. The THAT 1420 and 1430 go a step or two
further by improving over existing components. Both
incorporate OutSmartsä technology to tame the ab-
errant single-ended clipping behavior of conventional
cross-coupled output stages. The THAT 1430's de-
sign gives reasonably low output offset voltage with
only a resistor and a single film or ceramic capacitor,
though it is not pin-compatible with existing IC out-
put stages.
For more information on these or other THAT
Corporation integrated circuits, please contact us di-
rectly, or through one of our international distribu-
tors.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com