NSC LM831M Lm831 low voltage audio power amplifier Datasheet

LM831 Low Voltage Audio Power Amplifier
General Description
Features
The LM831 is a dual audio power amplifier optimized for
very low voltage operation. The LM831 has two independent amplifiers, giving stereo or higher power bridge (BTL)
operation from two- or three-cell power supplies.
The LM831 uses a patented compensation technique to reduce high-frequency radiation for optimum performance in
AM radio applications. This compensation also results in
lower distortion and less wide-band noise.
The input is direct-coupled to the LM831, eliminating the
usual coupling capacitor. Voltage gain is adjustable with a
single resistor.
Y
Y
Y
Y
Y
Low voltage operation, 1.8V to 6.0V
High power, 440 mW, 8X, BTL, 3V
Low AM radiation
Low noise
Low THD
Applications
Y
Y
Y
Y
Portable tape recorders
Portable radios
Headphone stereo
Portable speakers
Typical Application
Dual Amplifier with Minimum Parts
TL/H/6754 – 1
AV e 46 dB,BW e 250 Hz to 35 kHz
POUT e 220 mW/Ch,RL e 4X
C1995 National Semiconductor Corporation
TL/H/6754
RRD-B30M115/Printed in U. S. A.
LM831 Low Voltage Audio Power Amplifier
December 1994
Absolute Maximum Ratings
Storage Temperature, Tstg
Junction Temperature, Tj
Lead Temp. (Soldering, 10 sec.), TL
Thermal Resistance
iJC (DIP)
iJA (DIP)
iJC (SO Package)
iJA (SO Package)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Supply Voltage, VS
Input Voltage, VIN
Power Dissipation (Note 1), PD
Operating Temperature (Note 1), Topr
7.5V
g 0.4V
1.3W (M Package)
1.4W (N Package)
b 40§ C to a 85§ C
b 65§ C to a 150§ C
a 150§ C
a 260§ C
27§ C/W
75§ C/W
20§ C/W
95§ C/W
Electrical Characteristics
Unless otherwise specified, TA e 25§ C, VS e 3V, f e 1 kHz, test circuit is dual or BTL amplifier with minimum parts.
Symbol
Parameter
Typ
Tested Limit
Unit (Limit)
3
3
1.8
6
V(Min)
V(Max)
VIN e 0, Dual Mode
VIN e 0, BTL Mode
5
6
10
15
mA (Max)
mA (Max)
VIN e 0, BTL Mode
10
50
mV (Max)
25
15
35
k (Min)
k (Max)
VIN e 2.25 mVrms, f e 1 kHz,
Dual Mode
46
44
48
dB (Min)
dB (Max)
Supply Rejection
VS e 3V a 200 mVrms
46
30
dB (Min)
Power Out
VS e 3V, RL e 4X,
10% THD, Dual Mode
220
150
mW (Min)
PODL
Power Out Low, VS
VS e 1.8V, RL e 4X,
10% THD, Dual Mode
45
10
mW (Min)
POB
Power Out
VS e 3V, RL e 8X,
10% THD, BTL Mode
440
300
mW (Min)
Power Out Low, VS
VS e 1.8V, RL e 8X,
90
20
mW (Min)
52
40
dB (Min)
1
2
mA (Max)
VS
Operating Voltage
IQ
Supply Current
VOS
Output DC Offset
RIN
Input Resistance
AV
Voltage Gain
PSRR
POD
POBL
Conditions
@
f e 1 kHz
10% THD, BTL Mode
Sep
Channel Separation
IB
Input Bias Current
Referenced to VO e 200 mVrms
En0
Output Noise
Wide Band (250 E 35 kHz)
250
500
mV (Max)
THD
Distortion
VS e 3V, PO e 50 mW,
f e 1 kHz, Dual
0.25
1
% (Max)
Note 1: For operation in ambient temperatures above 25§ C, the device must be derated based on a 150§ C maximum junction temperature and a thermal resistance
of 98§ C/W junction to ambient for the M package or 90§ C/W junction to ambient for the N package.
Connection Diagram
Dual-In-Line Package
TL/H/6754 – 2
Top View
Order Number LM831M or N
See NS Package Number M16B or N16E
2
Typical Performance Characteristics
Supply Current vs Supply Voltage
PSRR vs Supply Voltage
Supply Current vs Temperature
PSRR vs Supply Voltage
DC Output vs Supply Voltage
Separation vs Supply Voltage
TL/H/6754 – 4
3
Typical Performance Characteristics (Continued)
Separation vs Frequency
Power Output vs Supply Voltage
Gain vs Frequency
Power Output vs Temperature
Gain vs Frequency
Bandwidth vs BW Capacitance
TL/H/6754 – 5
4
Typical Performance Characteristics (Continued)
Dual Mode, RL e 4X Distortion vs Frequency
Dual Mode, RL e 8X Distortion vs Frequency
Distortion vs Power Output (Note 2)
Distortion vs Power Output (Note 2)
Power Dissipation vs Power Output
Power Dissipation vs Power Output
TL/H/6754 – 6
5
Typical Performance Characteristics (Continued)
BTL Mode, RL e 8X Distortion vs Frequency
Device Dissipation vs Ambient Temperature
Distortion vs Power Output (Note 2)
Supply Current vs Power Output
Power Dissipation vs Power Output
Note 2: 1 kHz curve is measured with 400 Hz–30 kHz Filter.
TL/H/6754 – 7
6
Typical Applications
BTL Amplifier with Minimum Parts
TL/H/6754 – 8
AV e 52 dB, BW e 250 Hz to 25 kHz
POUT e 440 mW, RL e 8X
BTL Amplifier for Hi-Fi Quality
TL/H/6754 – 9
AV e 40 dB, BW e 20 Hz to 20 kHz
POUT e 440 mW, RL e 8X
(Dynamic Range Over 80 dB)
7
Typical Applications (Continued)
Dual Amplifier for Hi-Fi Quality
TL/H/6754 – 10
AV e 34 dB, BW e 50 Hz to 20 kHz
POUT e 220 mW/Ch, RL e 4X
(Dynamic Range Over 80 dB)
Low-Cost Power Amplifier (No Bootstrap)
TL/H/6754 – 11
POUT e 150 mW/Ch, BW e 300 Hz to 35 kHz
BTL Mode is also possible
*For 3-cell applications, the 120k resistor should be changed to 20K.
8
LM831 Circuit Description Refer to the external component diagram and equivalent schematic.
The capacitor CNF on Pin 2 provides unity DC gain for maximum DC accuracy.
Q2 provides voltage gain and the rest of the devices buffer
the output load from Q2’s collector.
Bootstrapping of Pin 5 by CBS allows maximum output
swing and improved supply rejection.
R5 is provided for bridge (BTL) operation.
The power supply is applied to Pin 9 and is filtered by resistor R1 and capacitor CBY on Pin 16. This filtered voltage at
Pin 16 is used to bias all of the LM831 circuits except the
power output stage. Resistor R0 generates a biasing current
that sets the output DC voltage for optimum output power
for any given supply voltage.
Feedback is provided to the input transistor Q1 emitter by
R6 and R7.
External Component Diagram
TL/H/6754 – 12
9
LM831 Equivalent Schematic
TL/H/6754 – 13
LM831 Circuit Description (Continued)
10
External Components (Refer to External Component Diagram)
Component
Min
Max
CO
Required to stabilize output stage.
Comments
0.33 mF
1 mF
Cc
Output coupling capacitors for Dual Mode. Sets a low-frequency pole in
the frequency response.
1
fL e
2qCcRL
100 mF
10,000 mF
CBS
Bootstrap capacitors. Sets a low-frequency pole in the power BW.
Recommended value is
1
CBS e
10 # 2q # fL # RL
22 mF or
(short Pins
4 & 12 to 9)
470 mF
CS
Supply bypass. Larger values improve low-battery performance by
reducing supply ripple.
47 mF
10,000 mF
CBY
Filters the supply for improved low-voltage operation. Also sets
turn-on delay.
47 mF
470 mF
CNF
Sets a low-frequency response. Also affects turn-on delay.
1
fL e
2q # CNF # (RAV a 80)
10 mF
100 mF
0.1 mF
1 mF
In BTL Mode, CNF on Pin 15 can be reduced without affecting the
frequency response. However, the turn-on ‘‘POP‘‘ will be worsened.
CBTL
Used only in the Bridge Mode. Connects the output of the first amplifier to
the inverting input of the other through an internal resistor. Sets a lowfrequency pole in one-half the frequency response.
1
fL e
2q # CBTL # 16k
CBW
Improves clipping waveform and sets the high-frequency bandwidth.
Works with an internal 16k resistor. (This equation applies for RAV i 0.
For 46 dB application, see BW–CBW curve.)
1
fH e
2q # CBW # 16k
See table below
RAV
Used to reduce the gain and improve the distortion and signal to noise. If
this is desired, CBW must also be used.
See table below
Typical AV
CBW
RAV
Min
Max
Short
Open
4700 pF
40 dB
82
100 pF
4700 pF
34 dB
240
270 pF
4700 pF
28 dB
560
500 pF
4700 pF
46 dB
11
Printed Circuit Layout for LM831N (Foil Side View) Refer to External Component Diagram
TL/H/6754 – 14
Note: Power ground pattern should be as wide as possible. Supply bypass capacitor should be as close to the IC as possible. Output compensation capacitors
should also be close to the IC.
12
Physical Dimensions inches (millimeters)
Molded SO Package (M)
Order Number LM831M
NS Package Number M16B
13
LM831 Low Voltage Audio Power Amplifier
Physical Dimensions inches (millimeters) (Continued)
Molded Dual-In-Line Package (N)
Order Number LM831N
NS Package Number N16E
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