Datasheet

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LM1972

www.ti.com

SNAS094D –APRIL 1995–REVISED MARCH 2013

LM1972 μPot 2-Channel 78dB Audio Attenuator with Mute

Check for Samples: LM1972

FEATURES

DESCRIPTION

The LM1972 is a digitally controlled 2-channel 78dB

• 3-Wire Serial Interface

audio attenuator fabricated on a CMOS process.

• Daisy-Chain Capability

Each channel has attenuation steps of 0.5dB from

• 104dB Mute Attenuation

0dB–47.5dB, 1.0dB steps from 48dB–78dB, with a

mute function attenuating 104dB. Its logarithmic

• Pop and Click Free Attenuation Changes

attenuation curve can be customized through

software to fit the desired application.

APPLICATIONS

The performance of a μPot is demonstrated through

• Automated Studio Mixing Consoles

its excellent Signal-to-Noise Ratio, extremely low

• Music Reproduction Systems

(THD+N), and high channel separation. Each μPot

• Sound Reinforcement Systems

contains a mute function that disconnects the input

signal from the output, providing a minimum

• Electronic Music (MIDI)

attenuation of 96dB. Transitions between any

• Personal Computer Audio Control

attenuation settings are pop free.

The LM1972's 3-wire serial digital interface is TTL

KEY SPECIFICATIONS

and CMOS compatible; receiving data that selects a

• Total Harmonic Distortion +

channel and the desired attenuation level. The Data-

Noise: 0.003 % (max)

Out pin of the LM1972 allows multiple μPots to be

daisy-chained together, reducing the number of

• Frequency response: 100 kHz (−3dB) (min)

enable and data lines to be routed for a given

• Attenuation range (excluding

application.

mute): 78 dB (typ)

• Differential attenuation: ±0.25 dB (max)

• Signal-to-noise ratio

(ref. 4 Vrms): 110 dB (min)

• Channel separation: 100 dB (min)

Typical Application

Connection Diagram

Figure 1. Typical Audio Attenuator Application Figure 2. 20-Lead SOIC - Top View

Circuit

See DW 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.

2All 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.

Summary of content (20 pages)

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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 LM1972 μPot 2-Channel 78dB Audio Attenuator with Mute Check for Samples: LM1972 FEATURES DESCRIPTION • • • • The LM1972 is a digitally controlled 2-channel 78dB audio attenuator fabricated on a CMOS process. Each channel has attenuation steps of 0.5dB from 0dB–47.5dB, 1.0dB steps from 48dB–78dB, with a mute function attenuating 104dB. Its logarithmic attenuation curve can be customized through software to fit the desired application.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) (3) Supply Voltage (VDD–VSS) 15V VSS − 0.2V to VDD + 0.
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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 Electrical Characteristics (1) (2) The following specifications apply for all channels with VDD = +6V, VSS = −6V, VIN = 5.5 Vpk, and f = 1 kHz, unless otherwise specified. Limits apply for TA = 25°C. Digital inputs are TTL and CMOS compatible. Symbol Parameter Conditions LM1972 Typical (3) IS Supply Current Inputs are AC Grounded THD+N Total Harmonic Distortion plus Noise VIN = 0.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com Timing Diagram Figure 3. Timing Diagram PIN DESCRIPTIONS Signal Ground (3, 19): Each input has its own independent ground, GND1 and GND2. Signal Input (4, 20): There are 2 independent signal inputs, IN1 and IN2. Signal Output (2, 17): There are 2 independent signal outputs, OUT1 and OUT2. Voltage Supply (13, 15): Positive voltage supply pins, VDD1 and VDD2. Voltage Supply (7, 18): Negative voltage supply pins, VSS1 and VSS2.
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LM1972 www.ti.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics 6 Supply Current vs Supply Voltage Supply Current vs Temperature Figure 4. Figure 5. Noise Floor Spectrum by FFT Amplitude vs Frequency THD vs Freq by FFT VDD − VSS = 12V Figure 6. Figure 7. THD vs VOUT at 1 KHz by FFT VDD − VSS = 12V Crosstalk Test Figure 8. Figure 9.
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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 Typical Performance Characteristics (continued) THD + N vs Frequency and Amplitude FFT of 1 kHz THD Figure 10. Figure 11. FFT of 20 kHz THD THD + N vs Amplitude Figure 12. Figure 13. THD + N vs Amplitude THD + N vs Amplitude Figure 14. Figure 15.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com APPLICATION INFORMATION ATTENUATION STEP SCHEME The fundamental attenuation step scheme for the LM1972 μPot is shown in Figure 16. This attenuation step scheme, however, can be changed through programming techniques to fit different application requirements. One such example would be a constant logarithmic attenuation scheme of 1dB steps for a panning function as shown in Figure 17.
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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 LM1972 Channel Attenuation vs Digital Step Value (Programmed 2.0dB Steps) Figure 18. LM1972 2.0dB Attenuation Step Scheme Figure 19. Mono Panning Circuit INPUT IMPEDANCE The input impedance of a μPot is constant at a nominal 40 kΩ. To eliminate any unwanted DC components from propagating through the device it is common to use 1 μF input coupling caps. This is not necessary, however, if the dc offset from the previous stage is negligible.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com The mute function is obtained during power-up of the device or by sending any binary data of 01111111 and above (to 11111111) serially to the device. The device may be placed into mute from a previous attenuation setting by sending any of the above data. This allows the designer to place a mute button onto his system which could cause a microcontroller to send the appropriate data to a μPot and thus mute any or all channels.
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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 Table 1. LM1972 Micropot Attenuator Register Set Description (continued) MSB: LSB 0111 1100 76.0 0111 1101 77.0 0111 1110 78.0 0111 1111 100.0 (Mute) 1000 0000 100.0 (Mute) ::::: :: 1111 1110 100.0 (Mute) 1111 1111 100.0 (Mute) Figure 20. Serial Data Format Transfer Process μPot SYSTEM ARCHITECTURE The μPot's digital interface is essentially a shift register, where serial data is shifted in, latched, and then decoded.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com DIGITAL DATA-OUT PIN The DATA-OUT pin is available for daisy-chain system configurations where multiple μPots will be used. The use of the daisy-chain configuration allows the system designer to use only one DATA and one LOAD/SHIFT line per chain, thus simplifying PCB trace layouts.
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LM1972 www.ti.com SNAS094D – APRIL 1995 – REVISED MARCH 2013 CLICKS AND POPS So, why is that output buffer needed anyway? There are three answers to this question, all of which are important from a system point of view. The first reason to utilize a buffer/amplifier at the output of a μPot is to ensure that there are no audible clicks or pops due to attenuation step changes in the device.
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LM1972 SNAS094D – APRIL 1995 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision C (March 2013) to Revision D • 14 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 18-Oct-2013 continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM1972MX/NOPB Package Package Pins Type Drawing SOIC DW 20 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 1000 330.0 24.4 Pack Materials-Page 1 10.9 B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 13.3 3.25 12.0 24.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM1972MX/NOPB SOIC DW 20 1000 367.0 367.0 45.
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