LM1971

Overture

Audio Attenuator Series

Digitally Controlled 62 dB Audio Attenuator with/Mute

General Description

The LM1971 is a digitally controlled single channel audio at-
tenuator fabricated on a CMOS process. Attenuation is vari-
able in 1 dB steps from 0 dB to -62 dB. A mute function dis-
connects 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 Distor-
tion (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 LM1971 is controlled 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 DATA pin receives serial data on the rising edge of
each CLOCK pulse, allowing the desired attenuation setting
to be selected.

Key Specifications

Total harmonic distortion

0.0008% (typ)

Frequency response

200 kHz (-3 dB) (typ)

Attenuation range (excluding mute)

62 dB (typ)

Dynamic range

115 dB (typ)

Mute attenuation

102 dB (typ)

Features

3-wire serial interface

Mute function

Click and pop free attenuation changes

8-pin plastic DIP and SO packages available

Applications

Communication systems

Cellular Phones and Pagers

Personal computer audio control

Electronic music (MIDI)

Sound reinforcement systems

Audio mixing automation

Typical Application

Overture

is a trademark of National Semiconductor Corporation.

DS012353-1

FIGURE 1. Typical Audio Attenuator Application Circuit

May 1999

LM1971

Overture

Audio

Attenuator

Series

Digitally

Controlled

Audio

Attenuator

with

Mute

DS012353

www.national.com

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

15V

Voltage at any pin

(GND -0.2V) to (V

+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

MIN

MAX

-20°C

+85°C

Thermal Resistance

M08A Package,

167°C/W

N08E Package,

102°C/W

Supply Voltage

4.5V to 12V

Electrical Characteristics

(Notes 1, 2)

The following specifications apply for V

= +12V (V

REF

IN = +6V), V

= 5.5 V

, and f = 1 kHz, unless otherwse specified.

Limits apply for T

= 25°C. Digital inputs are TTL and CMOS compatible.

Symbol

Parameter

Conditions

LM1971

Units

(Limits)

Typical

(Note 5)

Limit

(Note 6)

Supply Current

Digital Inputs Tied to 6V

1.8

mA (max)

THD

Total Harmonic Distortion

= 0.5V

0 dB Attenuation

0.0008

0.003

% (max)

Noise

Input is AC Grounded

-12 dB Attenuation

A-Weighted (Note 7)

4.0

µV

Dynamic Range

Referenced to Full Scale = +6 V

115

Mute Attenuation

102

dB (min)

Attenuation Step Size Error

0 dB to -62 dB

0.009

0.2

dB (max)

Absolute Attenuation

Attenuation

0 dB

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)

LEAK

Analog Input Leakage Current

Input is AC Grounded

5.8

100

nA (max)

Frequency Response

20 Hz100 kHz

0.1

AC Input Impedance

Pin 8, V

= 1.0 V

, f = 1 kHz

20
60

(min)

(max)

Input Current

Pins 4, 5, 6

1.0

100

nA (max)

CLK

Clock Frequency

MHz (max)

High-Level Input Voltage

Pins 4, 5, 6

2.0

V (min)

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

, and the ambient temperature T

. The maximum

allowable power dissipation is P

= (T

JMAX

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

JMAX

= +150°C, and the typical junction-to-ambient thermal resistance,

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

Note 4: Human body model, 100 pF discharged through a 1.5 k

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.

www.national.com

Pin Description

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

, as shown in

Figure 1 and Figure

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. Typically this
pin would be labeled "V

" 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

and Logic Ground. It is intended

that the LM1971 always be operated using a single volt-
age supply configuration, for which pin 3 (GND) should al-
ways be at system ground. If a bipolar or split-supply con-
figuration 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 micro-
controller 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.

(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

DS012353-10

Supply Current vs
Temperature

DS012353-11

Noise Floor
Analog Measurement

DS012353-12

THD + N vs Freq and Amp

DS012353-13

THD + N vs Freq and Amp

DS012353-14

Noise Floor Spectrum by FFT

DS012353-15

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