5173N24-U THAT, 5173N24-U Datasheet - Page 7

• Manufacturer Part Number: 5173N24-U
• Description: Microphone Preamplifiers 36V, 100mA
• Manufacturer: THAT

Specifications of 5173N24-U

• Rohs: yes
• Common Mode Rejection Ratio (min): - 9 dB
• Input Offset Voltage: - 1.75 mV to + 1.75 mV
• Maximum Operating Temperature: + 85 C
• Package / Case: QFN-24
• Input Voltage Range (max): 3.6 V, 17 V
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 3 V to 3.6 V, 4.75 V to 17 V
• Operating Temperature Range: - 40 C to + 85 C
• Supply Current: 2 uA, 7.6 mA
• Supply Voltage - Max: 3.6 V, 17 V
• Supply Voltage - Min: 3 V, 4.75 V
• Thd Plus Noise: 0.001 %
• Voltage Gain Db: 60 dB

THAT5173
Audio Preamplifier Digital Controller IC
of the 5173. When enabled, it permits gain changes
to take place only when the signal is within ±12.5mV.
A timeout (set by external components R
Figures 8~11) ensures that a gain change will always
occur at the expiration of the timeout, in case the sig-
nal has not gotten within the voltage window by that
time.
zero-crossings will occur every 25ms. Accordingly,
THAT recommends that the timeout be set to less
than or equal to 25ms in order to ensure that gain
changes will be made at zero-crossings unless there
is some unusual low-frequency signal present. 22mS
is the time constant shown in the application sche-
matics. Of course, for special applications, the
designer may choose to disable the zero-crossing
detection and force immediate gain changes without
regard to the signal condition.
changes are very quiet – barely audible when per-
formed in the absence of program, and all but inau-
dible with program material present.
Servo and DC Offsets
servo amplifier which minimizes dc offset at the out-
put. Practically, it is impossible to ensure that the
input offset voltage of the analog gain stage is low
enough to maintain low output dc offset at high
gains. (For <10mV output offset, the input offset at
~60dB gain would have to be under 10μV!) On the
other hand, it is not too difficult to make amplifiers
with under 1.75mV input offset. By using such an
amplifier in feedback around the analog gain stage, it
is possible to generate a correction voltage that main-
tains low output offset from the circuit as a whole.
under 1.75mV input offset voltage. It requires two
large non-polar capacitors in feedback around each
half of the amp to form an integrator. The integra-
tor’s input is connected to the gain stage’s output,
and the integrator’s output is applied to the gain
stage’s input. As the loop settles, the gain stage’s out-
put will be driven to the input offset voltage of the
servo. The loop time constant must be set long
enough so as not to interfere with low audio-
frequency signals.
(C
and R
servo, form a 2nd order highpass filter whose
4
The period of a 20Hz waveform is 50ms and thus
With the zero-crossing feature enabled, gain
The 5173 also includes an integrated differential
The integrated differential servo amplifier has
The combination of the input coupling capacitors
and C
2
– which form a load for C
5
in Figures 8~11), the bias resistors (R
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Copyright © 2012, THAT Corporation; All rights reserved.
4
and C
T
5
), and the
and C
T
in
Page 7 of 20
1
characteristics change with the gain setting. The Q of
this filter is highest at the highest gain setting. (At low
gains, the behavior is governed almost entirely by the
input coupling network and bias resistors, since the
poles split and the one related to the servo moves
very low.) Assuming 1.2kΩ for R
for R
.63 (for approximately Butterworth response) if we
choose C
resistors (R
resistors (R
tion from the servo amp. Reducing R
lower the Q, while increasing them will raise the Q,
proportional to the square-root of resistance.
quency, f
preamp gain, K=1+(R
C
at the outputs, it does require time to react. When
gain is changed, particularly if a sudden large
increase in gain is initiated (e.g. 0dB to 60dB), the
servo output will not change instantaneously with the
gain change. Immediately after the gain increase, the
servo will be supplying a dc offset appropriate for the
lower gain, and the dc at the output will thus change,
on a transient basis, to a higher level. As the servo
acquires the new required value, the dc offset will be
driven down to under 1.75mV.
change, THAT recommends that gain be increased
slowly by sending many commands to the 5173 that
increase gain 3dB (one step) at a time, over a second
or more of total time. This replaces the one big
change in dc offset with a series of much smaller
ones, allowing the servo some time to settle (at least
partially) in between each step. Note that the problem
is much less audible during stepwise decreases in
gain, since the servo’s output is not amplified as
much at the new (lower) gain as it was at the previ-
ous one.
12
=C
We recommend a 1000:1 ratio between servo feed
Mathematically, we can express the cutoff fre-
f
Q =
While the servo is effective at minimizing dc offset
To minimize the sonic impact of the dc offset
o
7
13
=
and R
, and the source impedance is less than 1kΩ.
12
0
2
2 f
, and the Q as:
and C
1
0
7
8
and R
G
G
1
1
, we can set the highest Q to be about
and R
20k C
R
1
13
7
20k C
1
to be 1/2 the values of C
2
) to minimize any noise contribu-
8
) to the analog gain stage bias
13
K
7
4
/R
C
, where G is the
1
13
), R
Document 600166 Rev 01
, and
1
=R
1
and R
2
, R
7
7
2
=R
, and 1.2MΩ
and R
4
8
and C
, C
8
4
=C
will
5
.
5
,