1. All specifications are subject to change without notice.
2. Unless otherwise noted, T
A
=25ºC, V
CC
=+15V, V
EE
= -15V.
3. Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only; the functional operation of
the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
dental electrostatic discharge (ESD) or electrical over
stress (EOS) will damage the ICs. Other diodes
across the base-emitter junctions of the input
transistors prevent excessive reverse biasing of these
junctions (which would degrade the noise perfor-
mance of the input devices).
Other than the protection diodes, the 1510/1512
input pins are connected only to the bases of their
respective input devices. For proper operation, the
bases must be provided a source of dc bias that will
maintain the inputs within the IC's input common-
mode range. Figure 3 shows the simplest approach;
dc bias is supplied via R
1
and R
2
. At 1 kΩ each, they
will minimize pickup of unwanted noise and
interference, as well as generate relatively little noise
due to input current noise in the 1510/1512.
However, at high gains, their inherent voltage noise,
plus the 1510/1512's input current noise drawn
across these resistors, adds significantly to the noise
at the 1510/1512's output.
Because R
G
is dc coupled in the circuit of Fig-
ure 3, the dc level at the output of the 1510/1512 will
vary with gain. In most applications, the output
should be ac-coupled to the next stage. For applica-
tions where R
G
is variable (via a pot or switched
resistors) to allow gain adjustment, R
G
should be ac-
coupled as shown in Figure 4. By adding C
G
in series
with R
G
, dc gain is fixed (at unity for the 1510, and ½
for the 1512). This constrains the output dc offset to
just over +/-5 mV, and prevents it from varying with
gain. With this low offset, ac coupling of the output is
usually unnecessary.
C
G
must be large enough not to interfere with low-
frequency response at the
smallest values of R
G
. For
60 dB gain, R
G
=10
Ω
(1510) or R
G
=5
Ω
(1512). For a
-3 dB point of approximately 5 Hz, C
G
=3,300 µF (1510),
or C
G
=6,800 µF (1512). For other maximum gains or
minimum frequencies, scale C
G
accordingly.
Phantom Power
Phantom power is required for many condenser
microphones. THAT recommends the circuit of
Figure 5 when phantom power is included
4
. R
3
, R
4
,
and D
1
- D
6
are used to limit the current that flows
through the 1510/1512 inputs when the circuit
inputs (-In and +In) are shorted to ground while
phantom power is turned on. This causes C
4
and/or
C
5
to discharge through other circuit components,
often generating transient currents of several amps.
R
3
and R
4
should be at least 10
Ω
to limit destructive
currents. (Higher values further limit current flow,
4. In revisions 0 and 1 of this data sheet, we recommended using Schottky diodes (1N5819 types) at D
1
~ D
4
to protect the 1510/1512 inputs against overloads.
Subsequently, we discovered that the leakage of these diodes could cause problems with DC fluctuations (hence noise) at the 1510/1512 output. Upon further
investigation, we concluded that conventional rectifier diodes like the 1N4004 (the glass-passivated GP version) provide adequate protection and do not introduce
unacceptable leakage. Additionally, 1N4004 diodes are much cheaper and more readily available than the Schottky types.
Since publishing revision 4, we determined that the internal reverse-bias diodes between the pins +In/R
G2
and -In/R
G1
may be damaged by phantom power faults under
certain conditions. Small-signal diodes (D
5
and D
6
) avoid this problem by appearing in parallel with the internal diodes, diverting excess current around the 1510/1512.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
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