NSC LM1971N, LM1971M, LM1971-NRE, LM1971MX Datasheet

LM1971

Overture

™

Audio Attenuator Series

Digitally Controlled 62 dB Audio Attenuator with/Mute

General Description

The LM1971 is a digitally controlled single channel audio at­tenuator fabricated on a CMOS process. Attenuation is vari­able in 1 dB steps from 0 dB to −62 dB. A mute function dis­connects the input from the output, providing over 100 dB of
attenuation.

The performance of the device is exhibited by its ability to
change attenuation levels without audible clicks or pops. In
addition, the LM1971 features a low Total Harmonic Distor­tion (THD) of 0.0008%, and a Dynamic Range of 115 dB,
making it suitable for digital audio needs. The LM1971 is
available in both 8-pin plastic DIP or SO packages.

The LM1971iscontrolled by a TTL/CMOS compatible 3-wire
serial digital interface. The active low LOAD line enables the
data input registers while the CLOCK line provides system
timing. Its DATApin receives serial data on the rising edge of
each CLOCK pulse, allowing the desired attenuation setting
to be selected.

Key Specifications

n Total harmonic distortion 0.0008%(typ)
n Frequency response

>

200 kHz (−3 dB) (typ)

n Attenuation range (excluding mute) 62 dB (typ)
n Dynamic range 115 dB (typ)
n Mute attenuation 102 dB (typ)

Features

n 3-wire serial interface
n Mute function
n Click and pop free attenuation changes
n 8-pin plastic DIP and SO packages available

Applications

n Communication systems
n Cellular Phones and Pagers
n Personal computer audio control
n Electronic music (MIDI)
n Sound reinforcement systems
n Audio mixing automation

Typical Application

Overture™is a trademark of National Semiconductor Corporation.

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FIGURE 1. Typical Audio Attenuator Application Circuit

May 1999

LM1971

Overture

Audio Attenuator Series Digitally Controlled 62 dB Audio Attenuator with Mute

© 1999 National Semiconductor Corporation DS012353 www.national.com

Connection Diagram

Dual-In-Line Plastic or Surface Mount Package

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Top View

Order Number LM1971M or LM1971N

See NS Package Number M08A or N08E

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Absolute Maximum Ratings (Notes 1, 2)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage, V

DD

15V

Voltage at any pin (GND −0.2V) to (V

DD

+0.2V)
ESD Susceptibility (Note 4) 3000V
Soldering Information

N Package (10s)
M Package

Vapor Phase (60s)
Infrared (15s)

260˚C
215˚C

220˚C

Power Dissipation (Note 3) 150 mW

Junction Temperature 150˚C
Storage Temperature −65˚C to +150˚C

Operating Ratings (Notes 1, 2)

Temperature Range

T

MIN

≤ TA≤ T

MAX

−20˚C ≤ TA≤ +85˚C

Thermal Resistance

M08A Package, θ

JA

167˚C/W

N08E Package, θ

JA

102˚C/W

Supply Voltage 4.5V to 12V

Electrical Characteristics (Notes 1, 2)

The following specifications apply for V

DD

=

+12V (V

REF

IN=+6V), V

IN

=

5.5 V

pk

, and f=1 kHz, unless otherwse specified.

Limits apply for T

A

=

25˚C. Digital inputs are TTL and CMOS compatible.

Symbol Parameter Conditions

LM1971

Units

(Limits)

Typical

(Note 5)

Limit

(Note 6)

I

S

Supply Current Digital Inputs Tied to 6V 1.8 3 mA (max)

THD Total Harmonic Distortion V

IN

= 0.5V

pk

@

0 dB Attenuation 0.0008 0.003

%

(max)

e

IN

Noise Input is AC Grounded

@

−12 dB Attenuation

A-Weighted (Note 7)

4.0 µV

DR Dynamic Range Referenced to Full Scale=+6 V

pk

115 dB

A

M

Mute Attenuation 102 96 dB (min)
Attenuation Step Size Error 0 dB to −62 dB 0.009 0.2 dB (max)
Absolute Attenuation Attenuation

@

0dB

Attenuation

@

−20 dB

Attenuation

@

−40 dB

Attenuation

@

−60 dB

Attenuation

@

−62 dB

0.1

−20.3

−40.5

−60.6

−62.6

0.5

−19.0

−38.0

−57.0

−59.0

dB (min)
dB (min)
dB (min)
dB (min)
dB (min)

I

LEAK

Analog Input Leakage Current Input is AC Grounded 5.8 100 nA (max)
Frequency Response 20 Hz–100 kHz

±

0.1 dB

R

IN

AC Input Impedance Pin 8, V

IN

=

1.0 V

pk

,f=1 kHz 40 20

60

kΩ (min)

kΩ (max)

I

IN

Input Current

@

Pins 4, 5, 6@0V<V

IN

<

5V 1.0 100 nA (max)

f

CLK

Clock Frequency 3 2 MHz (max)

V

IH

High-Level Input Voltage

@

Pins 4, 5, 6 2.0 V (min)

V

IL

Low-Level Input Voltage

@

Pins 4, 5, 6 0.8 V (max)

Note 1:

Absolute Maximum Ratings

indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits.

Electrical Characteristics

state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.

Note 2: All voltages are measured with respect to the GND pin (pin 3), unless otherwise specified.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T

JMAX

, θJA, and the ambient temperature TA. The maximum

allowable power dissipation is P

D

=

(T

JMAX–TA

)/θJAor the number given in the Absolute Maximum Ratings, whichever is lower. For the LM1971N and LM1971M,

T

JMAX

=

+150˚C, and the typical junction-to-ambient thermal resistance, θ

JA

, when board mounted is 102˚ C/W and 167˚ C/W, respectively.

Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Typicals are measured at 25˚C and represent the parametric norm.
Note 6: Limits are guarantees that all parts are tested in production to meet the stated values.
Note 7: Due to production test limitations, there is no limit for the Noise test. Please refer to the noise measurements in the Typical Performance Characteristics sec-

tion.

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Pin Description

V

REF

IN (1): The V

REF

IN pin provides the reference for the
analog input signal. This pin should be biased at half of
the supply voltage, V

DD

, as shown in

Figure 1

and

Figure

6

.

OUT (2): The attenuated analog output signal comes from
this pin.

GND (3): The GND pin references the digital input signals
and is the lower voltage reference for the IC. Typicallythis
pin would be labeled “V

SS

” but the ground reference for
the digital logic input control is tied to this same point. With
a higher pin-count there would generally be separate pins
for these functions; V

SS

and Logic Ground. It is intended
that the LM1971 always be operated using a single volt­age supply configuration, for which pin 3 (GND) should al­ways be at system ground. If a bipolar or split-supply con­figuration are desired, level shifting circuitry is needed for
the digital logic control pins as they would be referenced
through pin 3 which would be at the negative supply. It is
highly recommended, however, that the LM1971 be used
in a unipolar or single-supply configuration.

LOAD (4): The LOAD input accepts a TTL or CMOS level
signal. This is the enable pin of the device, allowing data
to be clocked in while this input is low (0V). The GND pin
is the reference for this signal.

DATA (5): The DATA input accepts a TTL or CMOS level
signal. This pin is used to accept serial data from a micro­controller that will be latched and decoded to change the
channel’s attenuation level. The GND pin is the reference
for this signal.

CLOCK (6): The CLOCK input accepts a TTL or CMOS
level signal. The clock input is used to load data into the
internal shift register on the rising edge of the input clock
waveform. The GND pin is the reference for this signal.

V

DD

(7): The positive voltage supply should be placed to

this pin.
IN (8): The analog input signal should be placed to this

pin.

Typical Performance
Characteristics

Supply Current vs
Supply Voltage

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Supply Current vs
Temperature

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Noise Floor
Analog Measurement

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THD+NvsFreq and Amp

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THD+NvsFreq and Amp

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Noise Floor Spectrum by FFT

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