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 impli ed. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
These diodes reduce the likelihood that accidental
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 performance 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 interfer-
ence, 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
Figure 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
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. Subse -
quently, 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 d o 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, MA 01757-1656; USA
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