THAT1420 Datasheet, PDF (6/8 Pages) List of Unclassifed Manufacturers – Balanced Line Drivers

Page 6
THAT1420/1430 Balanced Line Driver
Preliminary Information
Vcc
C1
R1
C4
100n
100n
1M0
6
7
In
4
Vcc
In ^Cap1
8
Out+
3 _{GnVdeeCap2Out1-}
2 ^U1
5
THAT1430
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 5. Basic THAT 1430 application circuit with output common mode offset reduction
tual worst case peak level for various types of music
and speech will be flat out to 5kHz, and roll off at
6dB/octave above this frequency. Thus the peak lev-
els at 20kHz will be 12dB below those at 5kHz.
Using these, we can calculate the required slew
rate and current drive. Since both outputs can swing
±11V, the V_Peak is actually 22V (below 5kHz), and at
20kHz, V_Peak is 5.5V. Therefore,
dV
dt
=
2p ´ 5.5V
´ 20kHz
=
0.69
V
ms
As a consequence,
i
=
500
ft
´(30
pF
ft
+
25
pF
ft
+
25
pfFt ₎
´
0.69
V
ms
»
28mA
Thus, driving this 40nF cable requires 28mA_Peak
(well within the 1420/1403’s capabilities). Figure 4
shows the most basic connection between the THAT
1420 and a typical line receiver (like the THAT
1243). The only external components that are abso-
lutely required are the local 100nF bypass capaci-
tors, and these could, in fact, be shared with another
nearby component. There are no common mode out-
put offset reduction capacitors, and the line driver’s
outputs are connected directly to their respective
sense inputs. The outputs are also DC coupled to the
line receiver. If large common mode voltages are ex-
pected, the designer may choose to incorporate large,
non-polarized capacitors to isolate the THAT 1420’s
outputs.
Figure 5 shows the basic THAT 1430 applications
circuit. This circuit includes external components
for common mode offset reduction. This IC is spe-
cially designed to allow common mode offset reduc-
tion with only a small resistor and capacitor, and is
ideal for new designs where space is at a premium.
Other considerations that apply to the THAT 1420
apply to the THAT 1430.
Figure 6 shows a THAT 1420 with common mode
offset reduction, RFI protection and surge protection,
but these last two additions could be added to the
THAT 1430 as well. One should also note that the
THAT 1420 is pin-for-pin compatible with industry
standard line drivers.
These line drivers can easily drive cables hun-
dreds of feet in length without becoming unstable,
but attaching such a long cable can act as an antenna
(even for AM stations) which can pick up RFI and di-
rect it into the circuit. C3 and C8 are 100pF capaci-
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com