PGA2500 SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 Digitally Controlled Microphone Preamplifier FEATURES D Fully Differential Input-to-Output Architecture D Digitally Controlled Gain Using Serial Port D D D D D D D D D D Interface: − Gain Range: 10dB through 65dB, 1dB per step − Unity (0dB) Gain Setting via Serial Port or Dedicated Control Pin Dynamic Performance: − Equivalent Input Noise with ZS = 150Ω and Gain = 30dB: −128dBu − Total Harmonic Distortion plus Noise (THD+N) with Gain = 30dB: 0.0004% 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 PGA2500 Devices Dedicated Input Pin for Selecting Unity Gain Overload Output Pin Provides Clipping Indication Four General-Purpose Digital Output Pins Requires ±5V Power Supplies Available in an SSOP-28 Package APPLICATIONS D Microphone Preamplifiers and Mixers D Digital Mixers and Recorders DESCRIPTION The PGA2500 is a digitally controlled, analog microphone preamplifier designed for use as a front end for highperformance audio analog-to-digital converters (ADCs). The PGA2500 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. The PGA2500 features a gain range of 10dB through 65dB (1dB/step), along with a unity gain setting. The wide gain range allows the PGA2500 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 PGA2500 devices. Four programmable digital outputs are provided for controlling the external switching of input pads, phantom power, high pass filters, and polarity reversal functions. The PGA2500 requires both +5V and −5V power supplies and is available in a small SSOP-28 package. 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. All trademarks are the property of their respective owners. Copyright 2003, Texas Instruments Incorporated ! ! www.ti.com " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 ABSOLUTE MAXIMUM RATINGS Over operating free-air temperature range unless otherwise noted(1) PGA2500 UNIT Supply Voltage, VA+ +5.5 V Supply Voltage, VA− −5.5 V Supply Voltage, VD− −5.5 V Voltage Difference, VA− to VD− Less than 300 mV Analog input voltage (VA−) −0.3 to (VA+) +0.3 V Digital input voltage −0.3 to (VA+) + 0.3 V −40 to +85 °C Operating Temperature Range This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. Storage Temperature Range −60 to +150 °C (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied. ORDERING INFORMATION PRODUCT PACKAGE-LEAD PACKAGE DESIGNATOR(1) SPECIFIED TEMPERATURE RANGE PACKAGE MARKING PGA2500 SSOP-28 DB −40°C −40 C to +85 +85°C C PGA2500I (1) For the most current specifications and package information, refer to our web site at www.ti.com. 2 ORDERING NUMBER TRANSPORT MEDIA, QUANTITY PGA2500IDB Rails, 48 PGA2500IDBR Tape and Reel, 1000 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 ELECTRICAL CHARACTERISTICS All parameters specified with TA = +25°C, VA+ = +5V, VA− = −5V, VD− = −5V, and VCOMIN = 0V, unless otherwise noted. PGA2500 PARAMETER DC Characteristics Step Size Gain Error TEST CONDITIONS MIN TYP Gain = 10dB through 65dB All Gain Settings 1 0.5 Gain = 0dB, VOUT = 3.5VRMS, VCOMIN = 0V Gain = 30dB, VOUT = 3.5VRMS, VCOMIN = 0V −114 −108 MAX UNIT dB dB AC Characteristics THD+N with fIN = 1kHz Analog Input Maximum Input Voltage Input Resistance Per Input Pin Differential Gain = 0dB VA− +1.5 −108 −102 dB dB VA+ −2.0 V Ω Ω 4600 9200 Analog Output Output Voltage Range Output Offset Voltage Input Referred Offset Output Resistive Loading VCOMIN = 0V, RL = 600Ω DC Servo On, Any Gain DC Servo Off, Gain = 30dB VA− +0.9 ±0.04 ±1 600 Load Capacitance Stability Short Circuit Current Digital Characteristics High-Level Input Voltage, VIH Low-Level Input Voltage, VIL High-Level Output Voltage, VOH Low-Level Output Voltage, VOL VA+ −0.9 ±1 10-second duration IO = 200µA IO = −3.2mA 100 pF 100 mA +2.0 −0.3 (VA+) − 1.0 Input Leakage Current, IIN V mV mV Ω VA+ 0.8 2 0.4 V V V V 10 µA 6.25 MHz ns Switching Characteristics Serial Clock (SCLK) Frequency Serial Clock (SCLK) Pulse Width Low fSCLK tPH 0 80 Serial Clock (SCLK) Pulse Width High tPL 80 ns SDI Setup Time tSDS 20 ns SDI Hold Time CS Falling to SCLK Rising tSDH tCSCR 20 90 ns ns SCLK Falling to CS Rising tCFCS 35 ns Input Timing Output Timing CS Low to SDO Active tCSO 35 ns SCLK Falling to SDO Data Valid CS High to SDO High Impedance tCFDO tCSZ 60 100 ns ns Power Supply Operating Voltage VA+ VA− +4.75 −4.75 +5 −5 +5.25 −5.25 V V VD− −4.75 −5 −5.25 V Quiescent Current IA+ IA− VA+ = +5V VA− = −5V 30 30 40 40 mA mA ID− VD− = −5V 1 2 mA 3 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 PIN CONFIGURATION GPO1 1 28 AGND GPO2 2 27 V IN + GPO3 3 26 V IN − GPO4 4 25 V COM IN OVR 5 24 C S1 1 DGND 6 23 C S1 2 DCEN 7 22 C S2 1 0dB 8 21 C S2 2 ZCEN 9 20 VA− SDI 10 19 VA+ PGA2500 CS 11 18 VA+ SCLK 12 17 V OUT + SDO 13 16 V OUT − VD− 14 15 VA− PIN DESCRIPTIONS 4 PIN NUMBER NAME DESCRIPTION 1 GPO1 General-Purpose CMOS Logic Output 2 GPO2 General-Purpose CMOS Logic Output 3 GPO3 General-Purpose CMOS Logic Output 4 GPO4 General-Purpose CMOS Logic Output 5 OVR 6 DGND Digital Ground 7 DCEN DC Servo Enable (Active Low) 8 0dB Unity Gain Enable (Active High) 9 ZCEN 10 SDI Serial Data Input 11 CS Chip Select Input (Active Low) 12 SCLK Serial Data Clock Input 13 SDO Serial Data Output 14 VD− −5V Digital Supply 15 VA− −5V Analog Supply 16 VOUT− Analog Output, Inverting 17 VOUT+ Analog Output, Non-Inverting 18 VA+ +5V Analog Supply 19 VA+ +5V Analog Supply 20 VA− −5V Analog Supply 21 CS22 DC Servo Capacitor #2, Terminal 2 22 CS21 DC Servo Capacitor #2, Terminal 1 23 CS12 DC Servo Capacitor #1, Terminal 2 24 CS11 DC Servo Capacitor #1, Terminal 1 25 VCOMIN 26 VIN− Analog Input, Inverting 27 VIN+ Analog Input, Noninverting 28 AGND Over Range Output (Active High) Zero Crossing Detector Enable (Active High) Common Mode Voltage Input, 0V to +2.5V Analog Ground " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 TYPICAL CHARACTERISTICS EQUIVALENT INPUT NOISE (E.I.N.) AS A FUNCTION OF GAIN (with Z = 0Ω) −100 −102 −104 −106 −108 −110 −112 −114 −116 −118 −120 −122 −124 −126 −128 −130 −132 −134 −136 10 15 20 25 30 35 40 45 50 55 60 65 Gain (dB) E.I.N. (dBu) E.I.N. (dBu) All specifications at TA = +25°C, VA+ = +5V, VA− = −5V, VD− = −5V, and VCOMIN = 0V, unless otherwise noted. THD+N vs GAIN (with 4.0 VRMS Output and Z = 40Ω) EQUIVALENT INPUT NOISE (E.I.N.) AS A FUNCTION OF GAIN (with Z = 150Ω) −100 −102 −104 −106 −108 −110 −112 −114 −116 −118 −120 −122 −124 −126 −128 −130 10 15 20 25 30 35 40 45 50 55 60 65 Gain (dB) THD+N AND NOISE vs GAIN (0dB = 4VRMS) −80 0.01 THD+N and Noise (dB) THD+N (%) −85 0.001 THD+N with Z = 40Ω −90 −95 −100 −105 Noise with Z = 0Ω −110 −115 −120 −125 −130 0.0001 10 15 20 25 30 35 40 45 Gain (dB) 50 55 60 65 10 THD+N vs FREQUENCY (RS = 40Ω, R L = 600Ω, VCOMIN = 0V, BW = 22Hz to 22kHz) 0.1 THD+N Ratio (%) THD+N Ratio (%) VOUT = 4.0Vrms Differential for Gains = 10, 20, 30, 40, 50, and 60dB VOUT = 3.5Vrms Differential for Gain = 0dB 60dB 50dB 40dB 0.001 20 25 30 35 40 45 Gain Set (dB) 50 55 60 65 THD+N vs FREQUENCY (RS = 40Ω, RL = 600Ω, VCOMIN = +2.5V, BW = 22Hz to 22kHz) 0.1 0.01 15 VOUT = 2.0Vrms Differential for Gains = 10, 20, 30, 40, 50, and 60dB VOUT = 1.0Vrms Differential for Gain = 0dB 60dB 0.01 50dB 40dB 10dB 0.001 30dB 10dB 0dB 0dB 30dB 20dB 20dB 0.0001 0.0001 20 100 1k Frequency (Hz) 10k 20k 20 100 1k 10k 20k Frequency (Hz) 5 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, VA+ = +5V, VA− = −5V, VD− = −5V, and VCOMIN = 0V, unless otherwise noted. THD+N vs FREQUENCY (RS = 40Ω, RL = 600Ω, VCOMIN = +2.5V, BW = 22Hz to 22kHz) BANDWIDTH vs GAIN 7 0.1 VOUT = 1.0Vrms Differential for All Gain Settings 6 0.01 Bandwidth (MHz) THD+N Ratio (%) 60dB 50dB 40dB 30dB 0.001 5 4 3 2 1 10dB 0dB 20dB 0 0.0001 20 100 1k 10k 20k 10 15 20 25 30 Frequency (Hz) THD+N vs OUTPUT AMPLITUDE THD+N (%) 0.1 0.01 0.001 0.0003 Gain = 30dB f = 1kHz VCOMIN = 0V RS = 40Ω RL = 600Ω 0.3 0.30 Output Amplitude (Vrms) 6 3.00 6.00 35 40 45 Gain (dB) 50 55 60 65 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 OVERVIEW The PGA2500 is a digitally controlled microphone preamplifier integrated circuit designed for amplifying the output of dynamic and condenser microphones and driving high performance audio analog-to-digital converters (ADCs). A functional block diagram of the PGA2500 is shown in Figure 1. The analog input to the preamplifier is provided differentially at the VIN+ and VIN− inputs (pins 27 and 26, respectively). The programmable gain amplifier can be programmed to either pass through the signal at unity gain, or apply 10dB to 65dB of gain to the input signal. The gain of the amplifier is adjustable over the full 10dB to 65dB range in 1dB steps. The differential output of the PGA2500 is made available at VOUT+ and VOUT− (pins 17 and 16, respectively). Gain is controlled using a serial port interface. The four-wire serial port interface is used to program the PGA2500 gain and support functions. A 16-bit control word is utilized to program these functions (see Figure 2, page 9). A serial data output pin provides support for daisy-chaining multiple PGA2500 devices on a single serial interface bus (see Figure 4, page 10). The differential analog output of the PGA2500 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 driving the DCEN input (pin 7) high or setting the DC bit in the serial control word to 1. Normally, the DCEN pin is connected to DGND to enable the DC servo, while the DC bit is set to 0. 0dB CS SCLK ZCEN SERIAL PORT and LOGIC CONTROL GPO1 GPO2 SDI SDO GPO3 GPO4 OVR VCOMIN VOUT+ VIN+ VIN− PGA VOUT− Gain Range AGND VA+ VA+ VA− 0dB or +10dB to +65dB CS1 1dB per step DC Servo VD− DGND VA− CS2 DCEN CS1 and CS2 are external DC servo integrator capacitors, and are connected across the CS11/CS12 and CS21/CS22 pins, respectively. Figure 1. PGA2500 Functional Block Diagram 7 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 Two external capacitors are required for the DC servo function, with one capacitor connected between CS11 and CS12 (pins 24 and 23), and the second capacitor connected between CS21 and CS22 (pins 22 and 21). Capacitor values up to 4.7µF may be utilized. However, larger valued capacitors will result in longer settling times for the DC servo loop. A value of 1µF is recommended for use in most microphone preamplifier applications. switching gain, thereby minimizing audible artifacts at the preamplifier output. Since 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. Forcing the ZCEN input low disables zero crossing detection, with gain changes occurring immediately when programmed. The PGA2500 includes a common-mode servo function. This function is enabled and disabled using the CM bit in the serial control word; see Figure 2. 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. In this case, the only connection between the source and the ground will be through the PGA2500 preamplifier input resistance. An overflow indicator output, OVR, is provided at pin 5. The OVR pin is an active high, CMOS-logic-level output. The overflow 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 OL bit. If OL = 0, then the threshold is set to 5.1VRMS differential, which is approximately −1dB below the specified output voltage range. If OL = 1, then the threshold is set to 4.0VRMS differential, which is approximately −3dB below the specified output voltage range. In this case, 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 commonmode rejection. Using the common-mode servo, overall common-mode rejection can be improved by suppressing low and medium frequency common-mode interference. The PGA2500 includes four programmable digital outputs, named GPO1 through GPO4 (pins 1 through 4, respectively), which are controlled via the serial port interface. All four 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. 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 ensured. The common-mode voltage control input, named VCOMIN (pin 25), allows the PGA2500 output and input to be DCbiased to a common-mode voltage between 0 and +2.5V. This allows for a DC-coupled interface between the PGA2500 preamplifier output and the inputs of common single-supply audio ADCs. A dedicated 0dB input (pin 8) is provided so that the gain of the PGA2500 may be forced to unity without using the serial port interface. The 0dB input overrides gain settings made through the serial port. While the 0dB input is active (forced high), the serial port register may be updated or data may passed through the serial interface to other PGA2500 devices in daisy-chain configuration. However, any changes made in the gain will not take effect until the 0dB input is driven low. The zero crossing control input, named ZCEN (pin 9), is provided for enabling and disabling the internal zero crossing detector function. Forcing the ZCEN input high enables the function. Zero crossing detection is used to force gain changes on zero crossings of the analog input signal. This limits the glitch energy associated with 8 ANALOG INPUTS AND OUTPUTS An analog signal is input differentially across the VIN+ (pin 27) and VIN− (pin 26) inputs. The input voltage range and input impedance are provided in the Electrical Characteristics table. The Applications Information section of this datasheet provides additional details regarding typical input circuit considerations when interfacing the PGA2500 to a microphone input. Both VIN+ and VIN− are biased at approximately 0.65V below the common-mode input voltage, supplied at VCOMIN (pin 25). The use of AC-coupling capacitors (see Figure 7, page 12) is highly recommended for the analog inputs of the PGA2500. 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 7 (page 12) for larger capacitors being used for EMI filtering which will satisfy this requirement. The analog output is presented differentially across VOUT+ (pin 17) and VOUT− (pin 16). 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 curves. " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 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 PGA2500 devices. Data on SDI is sampled on the rising edge of SCLK, while data is clocked out of SDO on the falling edge of SCLK. The serial port interface for the PGA2500 is comprised of four wires: CS (pin 11), SCLK (pin 12), SDI (pin 10), and SDO (pin 13). Figure 2 illustrates the serial port protocol, while Figure 3 and the Electrical Characteristics table provide detailed timing parameters for the port. 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. When the 0dB input (pin 8) is forced high, the gain set by the serial port register will be overridden. The serial port register may be updated while the 0dB input is forced high, but the programmed gain will not take effect until the 0dB input is forced low. CS SCLK SDI Data Ignored DC CM 0 OL D4 D3 D2 D1 0 0 G5 G4 G3 G2 G1 G0 Data Ignored SDO High Impedance DC CM 0 OL D4 D3 D2 D1 0 0 G5 G4 G3 G2 G1 G0 High Impedance DC Servo Enable (Active Low) Preamplifier Gain where N = G[5:0]DEC CM Servo Enable (Active High) For N = 0 Gain = 0dB Overload Indicator Bit (0 = 5.1VRMS, 1 = 4.0VRMS ) For N = 1 to 56 Gain (dB) = 9 + N Data for GPO4 For N = 57 to 63 Gain (dB) = 65 Data for GPO3 Data for GPO2 Data for GPO1 Figure 2. Serial Port Protocol CS t SDS t CSCR tCFCS tSDH SCLK SDI MSB SDO MSB tCSO tCFDO tCSZ Figure 3. Serial Port Timing Requirements 9 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 DAISY-CHAINING MULTIPLE PGA2500 PREAMPLIFIERS Since the serial port interface may be viewed as a serial in, serial out shift register, multiple PGA2500 preamplifiers may be connected in a cascaded or daisy-chained fashion, as shown in Figure 4. The daisy-chained PGA2500 devices behave as a 16 x N-bit shift register, where N is the VOUT+ VOUT− PGA2500 #1 number of cascaded PGA2500 devices. To program all of the devices, simply force CS low for 16 x N serial clock periods and clock in 16 x N bits of control data. The CS input is then forced high to latch in the new settings. A timing diagram for the daisy-chain application is shown in Figure 5. SDI DOUT CS CS SCLK VIN+ DATACLK DIN SDO VIN − VOUT+ Micro or DSP SDI VOUT− CS PGA2500 #2 SCLK VIN+ SDO VIN− VOUT+ SDI VOUT− CS PGA2500 #N SCLK VIN+ SDO VIN − Figure 4. Daisy-Chain Configuration for Multiple PGA2500 Preamplifiers CS SCLK SDI G0 DC Device #N DC G0 DC Device #2 Figure 5. Serial Port Operation for Daisy-Chain Operation 10 G0 Device #1 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 APPLICATION INFORMATION This section provides practical information for designing the PGA2500 into end applications. BASIC CIRCUIT CONFIGURATION A typical applications circuit, without the input and output circuitry, is shown in Figure 6. Power-supply bypass and DC servo capacitors are shown with recommended values. All capacitors should be placed as close as possible to the PGA2500 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). 1 2 To Relay Drivers, Switches, or Indicators 3 4 5 6 GPO1 The PGA2500 can be placed on a split ground plane, with the package located over the split. 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 25), 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 are level-shifted by the value of the bias voltage. AGND GPO2 GPO3 VIN+ VIN− GPO4 OVR VCOMIN DGND CS11 7 8 To/From MPU, MCU, DSP, or Logic 9 10 11 12 13 0.1µF 4.7µF + 14 0.1µF 0.1µF 15 20 28 CS12 DCEN 0dB ZCEN SDI CS PGA2500 CS21 CS22 VOUT+ VOUT− 27 25 24 VD− VA− VA− 1µF 0Ω(1) 0.1µF(1) To Optional Common−Mode Voltage 23 22 1µF 21 17 To Analog Output Circuit 16 SCLK SDO From Analog Input Circuit 26 19 18 0.1µF 0.1µF 4.7µF + VA− VA− VA+ 4.7µF + = Analog Ground Connect Digital and Analog Grounds at one common return point in the circuit. 10Ω VA− = Digital Ground NOTE: (1) Install a 0Ω shunt or jumper only when connecting VCOMIN to analog ground. Install a 0.1µF ceramic capacitor (X7R type) only when connecting VCOMIN to a DC common−mode voltage source. Figure 6. Basic Circuit Configuration for the PGA2500 11 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 INPUT CIRCUIT CONSIDERATIONS have a high working voltage rating, with 50V being the minimum and 63V recommended for long term reliability. The input circuit for the PGA2500 must include several items that are common to most microphone preamplifiers. Figure 7 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 blocking capacitors, along with the PGA2500 input resistance, form a high-pass filter circuit. With the typical input resistance of the PGA2500 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 higher than required, since larger capacitors store more charge and increase the surge current seen at the preamplifier when a short circuit occurs on the microphone input connector. The microphone input is typically taken from a balanced XLR or TRS input connection (XLR shown). The 1000pF capacitors provide simple EMI filtering for the circuit. Additional filtering for low- or high-frequency noise may be added, depending upon 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 will be in parallel with the phantom power bias resistors and the PGA2500 input resistance to set the actual impedance seen by the microphone. To protect the PGA2500 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 due to their lower turn-on voltage compared to standard rectifier diodes. Power devices are required since the surge currents from a large valued blocking capacitor (47µF) can exceed 4.5 amps 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. Connections for +48V phantom power, required for condenser microphones, are shown in Figure 7. The phantom power requires an On/Off switch, as 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 PGA2500 inputs. The blocking capacitors are selected to The use of a series current-limiting resistor prior to the protection diodes will aid in handling surge currents, although the resistor will add 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. 10µF − 47µF 63WV + (3) VIN+ (2) 1 2 (4) 6.81kΩ 0.25W 1000pF Mic Input (4) VA+ VA− 1000pF (1) 3 1000pF 6.81kΩ 0.25W 10µF − 47µF 63WV + (3) (4) (4) (2) Phantom Power Switch +48V NOTES: (1) Bridging resistor, used to set the impedance seen by the microphone. (2) The blocking capacitor value is selected based upon the desired low frequency response. (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 7. Typical Input Circuit for the PGA2500 12 VIN− " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 OPERATION WITH VCOMIN = +2.5V Plots of THD+N vs Frequency are shown in the Typical Characteristics section of this datasheet for both VCOMIN = 0V and +2.5V. The performance difference can be seen when comparing the plots. The user needs to consider whether the difference is acceptable for the end application. When interfacing the analog outputs of the PGA2500 with audio ADC inputs, the converter will frequently have a common-mode DC output pin. This pin may be connected to the VCOMIN pin of the PGA2500 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 PGA2500 in this fashion. As a suggested alternative, the PGA2500 analog outputs may be AC-coupled to the ADC inputs, allowing the PGA2500 to operate with VCOMIN = 0V in order to achieve best performance. The AC-coupling capacitors will 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. Both the analog input and output pins of the PGA2500 will be level shifted by the VCOMIN voltage. The analog outputs will be shifted to the VCOMIN level, while the analog inputs will be shifted to approximately VCOMIN − 0.65V, due to the offset that normally exists on the input pins. The level shifting will limit the input and output swing of the PGA2500, reducing the overall signal-to-noise ratio and degrading the THD+N performance. Figure 8 illustrates a typical PGA2500 to audio ADC interface utilizing AC-coupling. In addition to the coupling capacitors, a passive RC filter is required as an anti-alias 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 will also allow the PGA2500 to operate near full signal swing without overdriving the ADC inputs. Given VCOMIN = +2.5V and gains of 10dB through 65dB, the output swing is limited to less than one-half that specified in the Electrical Characteristics table. The output will hard-clip at approximately a diode drop below the VA+ supply rail and a diode drop above analog ground. Figure 9 illustrates an application where the VCOMIN pin of the PGA2500 is connected to the common-mode DC output of the audio ADC, with a DC-coupled interface between the PGA2500 analog outputs and the ADC analog inputs. 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 will result in a substantial increase in distortion. PGA2500 Coupling Capacitors VOUT+ PGA R 2R + VOUT− VCOMIN CC1 + A/D Converter(1) CC2 C ADC Serial Data Output PCM or DSD R Attenuation and Anti−Alias Filter NOTE: (1) PCM1804, PCM4202, or PCM4204. Figure 8. PGA2500 Analog Output to ADC Analog Input Interface, AC-Coupled 13 " #$%% www.ti.com SBOS289A − NOVEMBER 2003 − REVISED DECEMBER 2003 A/D Converter(1) PGA2500 VOUT+ R C PGA VOUT− VCOMIN ADC Serial Data Output PCM or DSD R Anti−Alias Filter VCOM Output 0.1µF NOTE: (1) PCM1804, PCM4202, or PCM4204. Figure 9. PGA2500 Analog Output to ADC Analog Input Interface, DC-Coupled 14 PACKAGE OPTION ADDENDUM www.ti.com 6-Dec-2006 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty PGA2500IDB ACTIVE SSOP DB 28 48 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR PGA2500IDBG4 ACTIVE SSOP DB 28 48 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR PGA2500IDBR ACTIVE SSOP DB 28 1000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR PGA2500IDBRG4 ACTIVE SSOP DB 28 1000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR Lead/Ball Finish MSL Peak Temp (3) (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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. 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Addendum-Page 1 MECHANICAL DATA MSSO002E – JANUARY 1995 – REVISED DECEMBER 2001 DB (R-PDSO-G**) PLASTIC SMALL-OUTLINE 28 PINS SHOWN 0,38 0,22 0,65 28 0,15 M 15 0,25 0,09 8,20 7,40 5,60 5,00 Gage Plane 1 14 0,25 A 0°–ā8° 0,95 0,55 Seating Plane 2,00 MAX 0,10 0,05 MIN PINS ** 14 16 20 24 28 30 38 A MAX 6,50 6,50 7,50 8,50 10,50 10,50 12,90 A MIN 5,90 5,90 6,90 7,90 9,90 9,90 12,30 DIM 4040065 /E 12/01 NOTES: A. B. C. D. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0,15. Falls within JEDEC MO-150 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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