PGA2505
PG
A
250
5
Burr-Brown Audio
www.ti.com ......................................................................................................................................................... SBOS396B – MARCH 2009 – REVISED JUNE 2009
™ Digitally-Controlled
MICROPHONE PREAMPLIFIER
FEATURES
APPLICATIONS
• FULLY DIFFERENTIAL lNPUT-TO-OUTPUT
ARCHITECTURE
• DIGITALLY-CONTROLLED GAIN USING SPI™:
– Gain Range: 9dB through 60dB,
3dB per Step
– Unity (0dB) Gain Setting via Serial Port
• DYNAMIC PERFORMANCE:
– Equivalent Input Noise with ZS = 150Ω
and Gain = 30dB: –123dBu
– Total Harmonic Distortion plus Noise
(THD+N) with Gain = 30dB: 0.0006%
• ZERO CROSSING DETECTION MINIMIZES
AUDIBLE ARTIFACTS WHEN GAIN
SWITCHING
• INTEGRATED DC SERVO MINIMIZES
OUTPUT OFFSET VOLTAGE
• COMMON-MODE SERVO IMPROVES CMRR
• FOUR-WIRE SERIAL CONTROL PORT
INTERFACE:
– Simple Interface to Microprocessor
or DSP Serial Ports
– Supports Daisy-Chaining of Multiple
PGA2505 Devices
• OVER-RANGE OUTPUT PIN PROVIDES
CLIPPING INDICATION
• FOUR GENERAL-PURPOSE
DIGITAL OUTPUT PINS
• ±5V POWER SUPPLIES
• AVAILABLE IN AN SSOP-24 PACKAGE
•
•
•
•
•
1
234
MICROPHONE PREAMPLIFIERS AND MIXERS
DIGITAL MIXERS AND RECORDERS
DIGITAL AUDIO EDITING SYSTEMS
BROADCAST EQUIPMENT
INTERCOMS
DESCRIPTION
The PGA2505 is a digitally-controlled, analog
microphone preamplifier designed for use as a
front-end for high-performance audio analog-to-digital
converters (ADCs). The PGA2505 features include
low noise, wide dynamic range, and a differential
signal path. An on-chip dc servo loop is employed to
minimize dc offset, while a common-mode servo
function may be used to enhance common-mode
rejection.
SoundPlus™
The PGA2505 features a gain range of 9dB through
60dB (3dB/step), along with a unity gain setting. The
wide gain range allows the PGA2505 to be used with
a variety of microphones. Gain settings and internal
functions are programmed using a 16-bit control
word, which is loaded using a simple serial port
interface. A serial data output pin provides support for
daisy-chained connection of multiple PGA2505
devices. Four programmable digital outputs are
provided for controlling the external switching of input
pads, phantom power, and high-pass filters. The
PGA2505 requires both +5V and –5V power supplies
and is available in a small SSOP-24 package.
1
2
3
4
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SoundPlus is a trademark of Texas Instruments Incorporated.
SPI is a trademark of Motorola, Inc..
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2009, Texas Instruments Incorporated
PGA2505
SBOS396B – MARCH 2009 – REVISED JUNE 2009 ......................................................................................................................................................... www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range, unless otherwise noted.
PGA2505
UNIT
Supply Voltage, AGND or DGND to VA+
–0.3 to +5.5
V
Supply Voltage, AGND or DGND to VA–
+0.3 to –5.5
V
Supply Voltage, AGND or DGND to VD–
+0.3 to –5.5
V
Voltage Difference, VA– to VD–
±0.3
V
Ground Difference, AGND to DGND
±0.3
V
Analog Input Voltage
(VA–) –0.3 to (VA+) +0.3
V
Digital Input Voltage
(DGND) – 0.3 to (VA+) + 0.3
V
±10
mA
Input Current of All Pins Except Supply
Power Dissipation
See Electrical Characteristics,
Thermal Resistance parameter
Junction Temperature Range, TJ
–40 to +150
°C
Operating Free-Air Temperature Range, TA
–40 to +85
°C
Storage Temperature Range, TSTG
–60 to +150
°C
Human Body Model (HBM)
2000
V
Charged Device Model (CDM)
1000
V
Machine Model (MM)
150
V
ESD Ratings
(1)
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not supported.
ORDERING INFORMATION (1)
(1)
PRODUCT
PACKAGE-LEAD
PACKAGE DESIGNATOR
PACKAGE MARKING
PGA2505
SSOP-24
DB
PGA2505I
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
2
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ELECTRICAL CHARACTERISTICS
At TA = +25°C, VA+ = +5V, VA– = –5V, VD– = –5V, and VCOMIN = 0V, unless otherwise noted.
PGA2505
PARAMETERS
CONDITIONS
MIN
TYP
MAX
UNIT
DC CHARACTERISTICS
Step Size
Gain = 9dB through 60dB
3
dB
Gain Error
All gain settings
±0.5
dB
fIN = 1kHz, Gain = 0dB, VOUT = 3.5VRMS
–110
–100
dB
fIN = 1kHz, Gain = 30dB, VOUT = 3.5VRMS
–105
–95
dB
VA+ –2.0
V
AC CHARACTERISTICS
THD+N
ANALOG INPUT
Maximum Input Voltage
Gain = 0dB
VA– +1.5
Input Resistance
Per Input Pin
4600
Ω
Differential
9200
Ω
ANALOG OUTPUT
Output Voltage Range
VCOMIN = 0V, RL = 600Ω
Output Offset Voltage
DC servo on, any gain
Input-Referred Offset
DC servo off, gain = 30dB
Output Resistive Loading
VA– +0.9
±0.08
VA+ –0.9
V
±1
mV
±1
mV
100
pF
100
mA
Ω
600
Load Capacitance Stability
Short Circuit Current
10-second duration
DIGITAL CHARACTERISTICS
High-Level Input Voltage
VIH
+2.0
VA+
V
Low-Level Input Voltage
VIL
–0.3
0.8
V
High-Level Output Voltage
VOH
IO = 200µA
Low-Level Output Voltage
VOL
IO = –3.2mA
Input Leakage Current
(VA+) – 1.0
IIN
V
0.4
V
2
10
µA
POWER SUPPLY
Operating Voltage
VA+
+4.75
+5
+5.25
V
VA–
–4.75
–5
–5.25
V
VD–
–4.75
–5
–5.25
V
Quiescent Current
IA+
VA+ = +5V
30
40
mA
IA–
VA– = –5V
30
40
mA
ID–
VD– = –5V
1
2
mA
÷85
°C
TEMPERATURE RANGE
Operating Free-Air Temperature
Range
TA
–40
Thermal Resistance
SSOP-24
θJA
High-K board
72
°C/W
θJC
High-K board
42
°C/W
3
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SWITCHING CHARACTERISTICS
Over operating free-air temperature range (unless otherwise noted).
PGA2505
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
6.25
MHz
fSCLK
Serial clock (SCLK) frequency
0
tPH
Serial clock (SCLK) pulse width low
80
ns
tPL
Serial clock (SCLK) pulse width high
80
ns
TIMING REQUIREMENTS
Over operating free-air temperature range (unless otherwise noted).
PGA2505
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
INPUT TIMING
tSDS
SDI setup time
20
ns
tSDH
SDI hold time
20
ns
tCSCR
CS falling to SCLK rising
90
ns
tCFCS
SCLK falling to CS rising
35
ns
OUTPUT TIMING
tCSO
CS low to SDO active
35
ns
tCFDO
SCLK falling to SDO data valid
60
ns
tCSZ
CS high to SDO high impedance
100
ns
SERIAL PORT TIMING DIAGRAM
CS
tSDS
tCSCR
tCFCS
tSDH
SCLK
SDI
MSB
SDO
MSB
tCSO
tCFDO
4
tCSZ
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Product Folder Link(s): PGA2505
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PIN CONFIGURATION
DB PACKAGE
SSOP-24
(TOP VIEW)
AGND
1
24
VIN+
GPO1
2
23
VIN-
GPO2
3
22
VCOMIN
GPO3
4
21
CS11
GPO4
5
20
CS12
OVR
6
19
CS21
DGND
7
18
CS22
SDI
8
17
VA-
CS
9
16
VA+
SCLK
10
15
VOUT+
SDO
11
14
VOUT-
VD-
12
13
VA-
PGA2505
PIN ASSIGNMENTS
TERMINAL
NAME
PIN#
AGND
1
Analog Ground
DESCRIPTION
GPO1
2
General-Purpose CMOS Logic Output
GPO2
3
General-Purpose CMOS Logic Output
GPO3
4
General-Purpose CMOS Logic Output
GPO4
5
General-Purpose CMOS Logic Output
OVR
6
Over Range Output (Active High)
DGND
7
Digital Ground
SDI
8
Serial Data Input
CS
9
Chip Select Input (Active Low)
SCLK
10
Serial Data Clock Input
SDO
11
Serial Data Output
VD–
12
–5V Digital Supply
VA–
13
–5V Analog Supply
VOUT–
14
Inverting Analog Output
VOUT+
15
Noninverting Analog Output
VA+
16
+5V Analog Supply
VA–
17
–5V Analog Supply
CS22
18
External DC Servo Capacitor #2, Terminal 2
CS21
19
External DC Servo Capacitor #2, Terminal 1
CS12
20
External DC Servo Capacitor #1, Terminal 2
CS11
21
External DC Servo Capacitor #1, Terminal 1
VCOMIN
22
Common Mode Voltage Input, 0V to +2.5V
VIN–
23
Inverting Analog Input
VIN+
24
Noninverting Analog Input
5
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TYPICAL CHARACTERISTICS
At TA = +25°C, VA+ = +5V, VA– = –5V, VD– = –5V, and VCOMIN = 0V, unless otherwise noted.
EQUIVALENT INPUT NOISE AS A FUNCTION OF GAIN
WITH ZS = 150Ω
-110
-110
-112
-112
-114
-114
-116
-116
EIN (dBu)
EIN (dBu)
EQUIVALENT INPUT NOISE AS A FUNCTION OF GAIN
WITH ZS = 0Ω
-118
-120
-118
-120
-122
-122
-124
-124
-126
-126
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Gain (dB)
Gain (dB)
Figure 1.
Figure 2.
THD+N vs GAIN
THD+N vs GAIN AND NOISE vs GAIN
-60
VOUT = 4.0VRMS
ZS = 40W
-70
THD+N and Noise (dB)
Total Harmonic Distortion + Noise (%)
0.01
0.001
-80
THD+N
with ZS = 40W
VOUT = 4.0VRMS
-90
-100
-110
Noise
with ZS = 0W
Reference 0dB = 4.0VRMS
-120
-130
0.0001
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Gain (dB)
Gain (dB)
Figure 3.
Figure 4.
THD + N vs FREQUENCY
(ZS = 40Ω, RL = 600Ω, VCOMIN = 0V, BW = 22Hz to 22kHz)
THD + N vs FREQUENCY
(ZS = 40Ω, RL = 600Ω, VCOMIN = +2.5V, BW = 22Hz to 22kHz)
0.1
VOUT = 4.0VRMS Differential for Gains =
12dB, 24dB, 30dB, 36dB, 48dB, and 60dB
VOUT = 3.5VRMS Differential for Gain = 0dB
0.01
48dB
24dB
30dB
0.001
VOUT = 2.0VRMS Differential for Gains = 12dB,
24dB, 30dB, 36dB, 48dB, and 60dB
60dB
60dB
36dB
THD+N Ratio (%)
THD+N Ratio (%)
0.1
0.01
VOUT = 1VRMS Differential for Gain = 0dB
48dB
36dB
0dB
0.001
30dB
12dB
0dB
12dB
24dB
0.0001
0.0001
20
100
1k
10k
20k
20
Frequency (Hz)
100
1k
10k
20k
Frequency (Hz)
Figure 5.
Figure 6.
6
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VA+ = +5V, VA– = –5V, VD– = –5V, and VCOMIN = 0V, unless otherwise noted.
THD + N vs FREQUENCY
(ZS = 40Ω, RL = 600Ω, VCOMIN = +2.5V, BW = 22Hz to 22kHz)
0.1
THD + N vs OUTPUT SWING
(ZS = 40Ω, RL = 600Ω, VCOMIN = 0V, BW = 22Hz to 22kHz)
0.1
VOUT = 1.0VRMS Differential for All Gain Settings
0.01
48dB
36dB
30dB
0.001
12dB
Gain = 30dB
f = 1kHz
0.0001
20
100
1k
0.01
0.001
0dB
24dB
THD+N (%)
THD+N Ratio (%)
60dB
10k
20k
0.0001
0.03
0.3
3
6
Output Amplitude (VRMS)
Frequency (Hz)
Figure 7.
Figure 8.
7
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APPLICATION INFORMATION
space
OVERVIEW
The differential analog output of the PGA2505 is
constantly monitored by a dc servo amplifier loop.
The purpose of the servo loop is to minimize the dc
offset voltage present at the analog outputs by
feeding back an error signal to the input stage of the
programmable gain amplifier. The error signal is then
used to correct the offset. The DC servo may be
disabled by setting the dc bit in the serial control word
to '1'.
The PGA2505 is a digitally-controlled microphone
preamplifier integrated circuit designed to amplify the
output of dynamic and condenser microphones and
drive high-performance audio analog-to-digital
converters (ADCs). A functional block diagram of the
PGA2505 is shown in Figure 9.
The analog input to the preamplifier is provided
differentially at the VIN+ and VIN– inputs (pins 24 and
23, respectively). The programmable gain amplifier
can be programmed to either pass through the signal
at unity gain, or apply 9dB to 60dB of gain to the
input signal. The gain of the amplifier is adjustable
over the full 9dB to 60dB range in 3dB steps. The
differential output of the PGA2505 is made available
at VOUT+ and VOUT– (pins 15 and 14, respectively).
Gain is controlled using a serial port interface.
Two external capacitors are required for the dc servo
function, with one capacitor connected between CS11
and CS12 (pins 21 and 20), and the second capacitor
connected between CS21 and CS22 (pins 19 and 18).
A capacitor value of 1µF is recommended for use in
most microphone preamplifier applications. Capacitor
values up to 4.7µF may be used. However, larger
valued capacitors result in longer settling times for
the dc servo loop. Smaller capacitors under 0.22µF
may result in additional distortion in the low frequency
audio bandwidth.
The four-wire serial port interface is used to program
the PGA2505 gain and support functions. A 16-bit
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).
GPO1
CS
GPO2
SCLK
SERIAL
PORT and
LOGIC
CONTROL
GPO3
GPO4
SDI
SDO
OVR
VCOMIN
VOUT+
VIN+
PGA
VOUT-
VIN(1)
Gain Range
(2)
AGND
VA+
VA-
CS1
DGND
DC
Servo
VD-
CS2
(1)
Gain Range: 0dB, or +9dB to +60dB (3dB/step).
(2)
CS1 and CS2 are external dc servo integrator capacitors, and are connected across the CS11/CS12 and CS21/CS22 pins,
respectively.
Figure 9. PGA2505 Functional Block Diagram
8
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The PGA2505 includes a common-mode servo
function. This function is enabled and disabled using
the CM bit in the serial control word; see Figure 10.
When enabled, the servo provides common-mode
negative feedback at the input differential pair,
resulting in very low common-mode input impedance.
The differential input impedance is not affected by
this feedback. This function is useful when the source
is floating, or has a high common-mode output
impedance.
When the source is floating, the only connection
between the source and the ground is through the
PGA2505 preamplifier input resistance. The input
common-mode parasitic current is determined by high
output impedance of the source, not by input
impedance of the amplifier. Therefore, input
common-mode interference can be reduced by
lowering the common-mode input impedance while at
the same time not increasing the input common-mode
current. Increasing common-mode current degrades
common-mode rejection. Using the common-mode
servo, overall common-mode rejection can be
improved by suppressing low and medium frequency
common-mode interference.
The common-mode servo function is designed to
operate with a total common-mode input capacitance
(including the microphone cable capacitance) of up to
10nF. Beyond this limit, stable servo operation is not
assured.
The common-mode voltage control input, named
VCOMIN (pin 22), allows the PGA2505 output and
input to be dc-biased to a common-mode voltage
between 0V and +2.5V and should not be left floating.
This configuration allows for a dc-coupled interface
between the PGA2505 preamplifier output and the
inputs of common single-supply audio ADCs.
The zero crossing control input is provided for
enabling and disabling the internal zero crossing
detector function. This function is enabled and
disabled using the ZC bit in the serial control word;
see Figure 10. Zero crossing detection is used to
force gain changes on zero crossings of the analog
input signal. This configuration limits the glitch energy
associated with switching gain, thereby minimizing
audible artifacts at the preamplifier output. Because
zero crossing detection can add some delay when
performing gain changes (up to 16ms maximum for a
detector timeout event), there may be cases where
the user may wish to disable the function. Setting the
ZC bit high enables zero crossing detection, with gain
changes occurring immediately when programmed.
An over-range indicator output, OVR, is provided at
pin 6. The OVR pin is an active high,
CMOS-logic-level output. The over-range output is
forced high when the preamplifier output voltage
exceeds one of two preset thresholds. The threshold
is programmed through the serial port interface using
the OR bit. If OR = '0', then the output threshold is set
to 5.1VRMS differential, which is approximately 1dB
below the specified output voltage range. If OR = '1',
then the output threshold is set to 4.0VRMS
differential, which is approximately 3dB below the
specified output voltage range.
The PGA2505 includes four programmable digital
outputs, named GPO1, GPO2, GPO3, and GPO4
(pins 2, 3, 4, and 5 respectively), that are controlled
via the serial port interface. These pins are
CMOS-logic-level outputs. These pins may be used
to control relay drivers or switches used for external
preamplifier functions, including input pads, filtering,
polarity reversal, or phantom power.
ANALOG INPUTS AND OUTPUTS
An analog signal is input differentially across the VIN+
(pin 24) and VIN– (pin 23) inputs. The input voltage
range and input impedance are provided in the
Electrical Characteristics table. The Applications
Information section of this data sheet provides
additional details regarding typical input circuit
considerations when interfacing the PGA2505 to a
microphone input.
Both VIN+ and VIN– are biased at approximately
0.65V below the common-mode input voltage,
supplied at VCOMIN (pin 22). The use of ac-coupling
capacitors (see Figure 10) is highly recommended for
the analog inputs of the PGA2505. If dc-coupling is
required for a given application, the user must take
this offset into account.
It is recommended that a small capacitor be
connected from each analog input pin to analog
ground. Values of at least 50pF are recommended.
See Figure 10 for larger capacitors used for EMI
filtering, which satisfies this requirement.
The analog output is presented differentially across
VOUT+ (pin 15) and VOUT– (pin 14). The output
voltage range is provided in the Electrical
Characteristics table. The analog output is designed
to drive a 600Ω differential load while meeting the
published THD+N specifications and typical
performance graphs.
Note that because the zero crossing detector requires
setup, the user should set the ZC bit as a first
operation. Subsequent changes in gain occur on the
zero crossings provided that the ZC bit setting is
maintained.
9
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SERIAL PORT OPERATION
The SCLK input is used to clock serial data into the
SDI pin and out of the SDO pin. The SDI pin
functions as the serial data input, and is used to write
the serial port register. The SDO pin is the shift
register serial output, and is used for either register
read-back or for daisy-chaining multiple PGA2505
devices. Data on SDI are sampled on the rising edge
of SCLK, while data are clocked out of SDO on the
falling edge of SCLK.
The serial port interface for the PGA2505 is
comprised of four wires: CS (pin 9), SCLK (pin 10),
SDI (pin 8), and SDO (pin 11). Figure 10 illustrates
the serial port protocol.
The CS input functions as the chip select and word
latch clock for the serial port. The CS input must be
low in order to clock data into and out of the serial
port. The control word is latched on a low-to-high
transition of the CS input.
The serial port ignores the SCLK and SDI inputs
when CS is high, and the SDO output is set to a high
impedance state while CS is high.
CS
SCLK
SDI
Data Ignored
DC
CM
ZC
OR
D4
D3
D2
D1
0
0
G5
G4
G3
G2
G1
G0
Data Ignored
SDO
High Impedance
DC
CM
ZC
OR
D4
D3
D2
D1
0
0
G5
G4
G3
G2
G1
G0
High Impedance
DC Servo Enable
(Active Low)
CM Servo Enable
(Active High)
Zero Crossing Detect
(Active High)
Over-Range Indicator Bit
(0 = 5.1VRMS, 1 = 4.0VRMS)
Data for GPO4
Preamplifier Gain
where N = G[5:0]DEC
For N = 0
Gain = 0dB
For N = 1 to 17
Gain (dB) = 6 + 3N
For N = 18 to 31
Gain = 60dB
Data for GPO3
Data for GPO2
Data for GPO1
Figure 10. Serial Port Protocol
10
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DAISY-CHAINING MULTIPLE PGA2505
PREAMPLIFIERS
Because the serial port interface may be viewed as a
serial in, serial out shift register, multiple PGA2505
preamplifiers may be connected in a cascaded or
daisy-chained fashion, as shown in Figure 11. The
daisy-chained PGA2505 devices behave as a 16 x
N-bit shift register, where N is the number of
cascaded PGA2505 devices.
VOUT+
To program all of the devices, simply force CS low for
16 x N serial clock periods and clock in 16 x N bits of
control data. The CS input is then forced high to latch
in the new settings.
A timing diagram for the daisy-chain application is
shown in Figure 12.
SDI
DOUT
CS
CS
VOUTPGA2505
#1
SCLK
VIN+
DATACLK
Microprocessor
or DSP
DIN
SDO
VIN-
VOUT+
SDI
VOUTCS
PGA2505
#2
SCLK
VIN+
SDO
VIN-
VOUT+
SDI
VOUTCS
PGA2505
#N
SCLK
VIN+
SDO
VIN-
Figure 11. Daisy-Chain Configuration for Multiple PGA2505 Preamplifiers
CS
SCLK
SDI
G0
DC
Device #N
G0
DC
G0
DC
Device #2
Device #1
Figure 12. Serial Port Operation for Daisy-Chain Operation
11
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505
PGA2505
SBOS396B – MARCH 2009 – REVISED JUNE 2009 ......................................................................................................................................................... www.ti.com
APPLICATION INFORMATION
This section provides practical information
designing the PGA2505 into end applications.
for
BASIC CIRCUIT CONFIGURATION
A typical application configuration, without the input
and output circuitry, is shown in Figure 13.
Power-supply bypass and dc servo capacitors are
shown with recommended values. All capacitors
should be placed as close as possible to the
PGA2505 package to limit inductive noise coupling.
Surface-mount capacitors are recommended (X7R
ceramic for the 0.1µF and 1µF capacitors, and low
ESR tantalum for the 4.7µF capacitors).
with analog and digital pins separated basically down
the center of the package. (Note that AGND is on the
opposite side.) However, there must be a low
impedance connection between the analog and digital
grounds at a common return point.
The dc common-mode input, VCOMIN (pin 22), can be
connected to analog ground or a dc voltage (such as
the reference or common voltage output of an audio
ADC). When biasing this input to a dc voltage, keep
in mind that both the analog output and input pins will
be level-shifted by the value of the bias voltage.
The PGA2505 can be placed on a split ground plane,
1
2
3
4
To Relay Drivers
and Switches
5
6
7
AGND
VIN+
GPO1
VIN-
GPO2
VCOMIN
GPO3
CS11
GPO4
OVR
CS12
DGND
CS21
CS22
8
9
To/From
MPU, MCU,
DSP, or Logic
10
11
VA-
SDI
CS
24
23
22
21
1mF
20
19
0W
0.1mF
1mF
18
17
0.1mF
4.7mF
+
PGA2505
SCLK
SDO
VAVA+
16
0.1mF
4.7mF
+
0.1mF
4.7mF
+
12
VDVA+
0.1mF
13
4.7mF
+
VA-
VOUT+
VOUT-
15
14
10W
VA-
Figure 13. Basic Circuit Configuration for the PGA2505
12
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505
PGA2505
www.ti.com ......................................................................................................................................................... SBOS396B – MARCH 2009 – REVISED JUNE 2009
INPUT CIRCUIT CONSIDERATIONS
The blocking capacitors, along with the PGA2505
input resistance, form a high-pass filter circuit. With
the typical input resistance of the PGA2505 specified
in the Electrical Characteristics table, the value of the
capacitor can be chosen to meet the desired low
frequency response for the end application. At the
same time, the value should be no greater than
required, because larger capacitors store more
charge and increase the surge current seen at the
preamplifier when a short circuit occurs on the
microphone input connector.
For proper operation, the input circuit for the
PGA2505 must include several items that are
common to most microphone preamplifiers. Figure 14
shows a typical input circuit configuration. Other
functions, such as input attenuation (pads), filters,
and polarity reversal switches are commonly found in
preamplifier circuits, but are not shown here in order
to focus on the basic input circuit requirements.
The microphone input is typically taken from a
balanced XLR or TRS input connection (XLR shown).
Three 1000pF capacitors provide simple EMI filtering
for the circuit. Additional filtering for low- or
high-frequency noise may be added, depending on
the end application environment. A bridging resistor is
shown and may be selected to provide the desired
overall input impedance required for a given
microphone. This resistance is in parallel with the
phantom power bias resistors and the PGA2505 input
resistance to set the actual impedance seen by the
microphone.
To protect the PGA2505 from large surge currents,
power Schottky diodes are placed on the input pins to
both the VA+ and VA– power supplies. Schottky
diodes are used because of the lower turn-on voltage
compared to standard rectifier diodes. Power devices
are required because the surge currents from a large
valued blocking capacitor (47µF) can exceed 4.5A for
a very short duration of time. It is recommended that
the Schottky diode chosen for this application be
specified for at least a 10A surge current.
The use of a series current-limiting resistor before the
protection diodes aids in handling surge currents,
although the resistor adds noise to the circuit. Select
a current-liming resistor value that is as high as
tolerable for the desired noise performance of the
preamplifier circuit.
Connections for +48V phantom power, required for
condenser microphones, are shown in Figure 14. The
phantom power requires an On/Off switch, because
dynamic microphones do not require phantom power
and may be damaged if power is applied.
DC-blocking capacitors are required between the
phantom power connections and the PGA2505
inputs. The blocking capacitors are selected to have
a high working voltage rating, with 50V being the
minimum and 63V recommended for long-term
reliability.
10mF - 47mF
63WV
+
(3)
VIN+
(2)
Mic Input
1
1000pF
(4)
6.81kW
0.25W
(4)
VA-
VA+
1000pF
2
3
(1)
1000pF
6.81kW
0.25W
Phantom
Power
Switch
10mF - 47mF
63WV
+
(3)
(4)
(4)
VIN-
(2)
+48V
(1)
Bridging resistor; used to set the impedance seen by the microphone.
(2)
NOTES: value is selected based upon the desired low frequency response.
The blocking capacitor
(3)
Current-limiting resistor. Select the highest value tolerable based upon input noise requirements.
(4)
Schottky diode; selected for fast turn-on and rated for a minimum of a 10A surge current. Recommended device is the
MBRA120LT3 from ON Semiconductor.
Figure 14. Typical Input Circuit for the PGA2505
13
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505
PGA2505
SBOS396B – MARCH 2009 – REVISED JUNE 2009 ......................................................................................................................................................... www.ti.com
OPERATION WITH VCOMIN = +2.5V
As a suggested alternative, the PGA2505 analog
outputs may be ac-coupled to the ADC inputs,
allowing the PGA2505 to operate with VCOMIN = 0V in
order to achieve best performance. The ac-coupling
capacitors affect the overall low-frequency response
of the preamplifier and converter combination, and
the user is advised to choose a value that best suits
the application requirements.
When interfacing the analog outputs of the PGA2505
with audio ADC inputs, the converter may frequently
have a common-mode dc output pin. This pin may be
connected to the VCOMIN pin of the PGA2505 in order
to facilitate a dc-coupled interface between the two
devices. The common-mode dc voltage level is
typically +2.5V, although some converters may have
a slightly lower value, usually between +2.1V and
+2.5V. There are several issues that must be
considered when operating the PGA2505 in this
fashion.
Figure 15 illustrates a typical PGA2505 to audio ADC
interface using ac-coupling. In addition to the coupling
capacitors, a passive RC filter is required as an
antialiasing filter for the converter. The vast majority
of audio ADCs are of the oversampling delta-sigma
variety, with a simple single-pole filter meeting the
anti-aliasing requirements for this type of converter.
Providing at least 6dB of attenuation also allows the
PGA2505 to operate near full signal swing without
overdriving the ADC inputs.
Both the analog input and output pins of the
PGA2505 are level-shifted by the VCOMIN voltage.
The analog outputs are shifted to the VCOMIN level,
while the analog inputs are shifted to approximately
VCOMIN – 0.65V, as a result of the offset that normally
exists on the input pins. The level-shifting limits the
input and output swing of the PGA2505, reducing the
overall signal-to-noise ratio and degrading the
THD+N performance.
Figure 16 illustrates an application where the VCOMIN
pin of the PGA2505 is connected to the
common-mode dc output of the audio ADC, with a
dc-coupled interface between the PGA2505 analog
outputs and the ADC analog inputs.
Given VCOMIN = +2.5V and gains of 0dB through
60dB, the output swing is limited to less than one-half
that specified in the Electrical Characteristics table.
The output hard-clips at approximately a diode drop
below the VA+ supply rail and a diode drop above
analog ground.
To ensure optimal performance, an output buffer to
the PGA2505 is recommended. Figure 17 illustrates
the use of an OPA1632 as the buffer. Additionally,
the feedback circuitry functions as the antialiasing
filter shown in Figure 15 and Figure 16. Having a
differential buffer with attenuation of 6dB or greater
also allows for the PGA2505 to maximize the output
signal swing, while ensuring that the input swing does
not exceed the full-scale input range of the ADC. An
OPA227 is used to drive the output common-mode of
the OPA1632.
Given VCOMIN = +2.5V and a gain of 0dB, the
practical maximum input or output voltage swing is
approximately 1.0VRMS differential. Increasing the
signal level much beyond this point results in a
substantial increase in distortion.
Plots of THD+N vs Frequency are shown in the
Typical Characteristics section of this data sheet for
both VCOMIN = 0V and +2.5V. The performance
difference can be seen when comparing the plots.
The user must consider whether the difference is
acceptable for the end application.
Coupling
Capacitors
PGA2505
VOUT+
CC1
+
A/D Converter
R
2R
PGA
+
VOUT-
VCOMIN
(1)
CC2
(1)
C
Serial Data Output
PCM or DSD
ADC
R
Attenuation and
Antialiasing Filter
Recommended devices are the PCM1804, PCM4202, PCM4204, PCM4220, or PCM4222.
Figure 15. PGA2505 Analog Output to ADC Analog Input Interface, AC-Coupled
14
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505
PGA2505
www.ti.com ......................................................................................................................................................... SBOS396B – MARCH 2009 – REVISED JUNE 2009
A/D Converter
PGA2505
VOUT+
R
C
PGA
VOUT-
VCOMIN
(1)
Serial Data Output
PCM or DSD
ADC
R
VCOM Output
Antialiasing Filter
0.1mF
(1)
Recommended devices are the PCM1804, PCM4202, PCM4204, PCM4220, or PCM4222.
Figure 16. PGA2505 Analog Output to ADC Analog Input Interface, DC-Coupled
+5V
470W
1nF
16
1kW
15
24
3
8
7
40.2W
5
VIN+
+
PGA2505
23
22
14
1kW
17
1
2
6
A/D Converter
VIN- V
2.7nF
OPA1632
4
(1)
COM
40.2W
1nF
470W
2
-5V
6
OPA227
1kW
3
0.1mF
(1)
Recommended devices are the PCM1804, PCM4202, PCM4204, PCM4220, or PCM4222.
Figure 17. PGA2505 Using OPA1632 as an Output Buffer
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (May, 2009) to Revision B ..................................................................................................... Page
•
Changed logo on document .................................................................................................................................................. 1
15
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PGA2505
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
PGA2505IDB
ACTIVE
SSOP
DB
24
60
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
PGA2505I
PGA2505IDBR
ACTIVE
SSOP
DB
24
2000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
PGA2505I
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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