Datasheet

APPLICATION INFORMATION
OVERVIEW
SERIAL
PORTand
LOGIC
CONTROL
CS
SCLK
SDI
SDO
OVR
V IN
COM
V +
OUT
V -
OUT
VD-
PGA
DC
Servo
C
(2)
S1
C
S2
V +
IN
V -
IN
AGND
VA-
VA+
DGND
GainRange
(1)
GPO1
GPO2
GPO3
GPO4
PGA2505
SBOS396B – MARCH 2009 – REVISED JUNE 2009 ......................................................................................................................................................... www.ti.com
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The differential analog output of the PGA2505 is
constantly monitored by a dc servo amplifier loop.
The PGA2505 is a digitally-controlled microphone
The purpose of the servo loop is to minimize the dc
preamplifier integrated circuit designed to amplify the
offset voltage present at the analog outputs by
output of dynamic and condenser microphones and
feeding back an error signal to the input stage of the
drive high-performance audio analog-to-digital
programmable gain amplifier. The error signal is then
converters (ADCs). A functional block diagram of the
used to correct the offset. The DC servo may be
PGA2505 is shown in Figure 9 .
disabled by setting the dc bit in the serial control word
The analog input to the preamplifier is provided
to '1'.
differentially at the V
IN
+ and V
IN
– inputs (pins 24 and
Two external capacitors are required for the dc servo
23, respectively). The programmable gain amplifier
function, with one capacitor connected between C
S11
can be programmed to either pass through the signal
and C
S12
(pins 21 and 20), and the second capacitor
at unity gain, or apply 9dB to 60dB of gain to the
connected between C
S21
and C
S22
(pins 19 and 18).
input signal. The gain of the amplifier is adjustable
A capacitor value of 1 µ F is recommended for use in
over the full 9dB to 60dB range in 3dB steps. The
most microphone preamplifier applications. Capacitor
differential output of the PGA2505 is made available
values up to 4.7 µ F may be used. However, larger
at V
OUT
+ and V
OUT
– (pins 15 and 14, respectively).
valued capacitors result in longer settling times for
Gain is controlled using a serial port interface.
the dc servo loop. Smaller capacitors under 0.22 µ F
The four-wire serial port interface is used to program
may result in additional distortion in the low frequency
the PGA2505 gain and support functions. A 16-bit
audio bandwidth.
control word is utilized to program these functions
(see Figure 10 ). A serial data output pin provides
support for daisy-chaining multiple PGA2505 devices
on a single serial interface bus (see Figure 11 ).
(1) Gain Range: 0dB, or +9dB to +60dB (3dB/step).
(2) C
S1
and C
S2
are external dc servo integrator capacitors, and are connected across the C
S11
/C
S12
and C
S21
/C
S22
pins,
respectively.
Figure 9. PGA2505 Functional Block Diagram
8 Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505