MAX4295_V01 [MAXIM]
Mono, 2W, Switch-Mode (Class D) Audio Power Amplifier;
| 型号： | MAX4295_V01 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Mono, 2W, Switch-Mode (Class D) Audio Power Amplifier |
| 文件： | 总15页 (文件大小：537K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1746; Rev 3; 3/05
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
General Description
Features
The MAX4295 mono, switch-mode (Class D) audio
power amplifier operates from a single +2.7V to +5.5V
supply. The MAX4295 has >85% efficiency and is
capable of delivering 2W continuous power to a 4Ω
load, making it ideal for portable multimedia and gener-
al-purpose high-power audio applications.
♦ +2.7V to +5.5V Single-Supply Operation
♦ 2W/Channel Output Power at 5V
0.7W/Channel Output Power at 3V
♦ 87% Efficiency (R = 4Ω, P
= 2W)
OUT
L
♦ 0.4% THD+N (R = 4Ω, f
= 125kHz)
L
OSC
The MAX4295 features a total harmonic distortion plus
♦ Logic-Programmable PWM Frequency Selection
(125kHz, 250kHz, 500kHz, 1MHz)
noise (THD+N) of 0.4% (f
= 125kHz), low quiescent
OSC
current of 2.8mA, high efficiency, and clickless power-
up and shutdown. The SHDN input disables the device
and limits supply current to <1.5µA. Other features
include a 1A current limit, thermal protection, and
undervoltage lockout.
♦ Low-Power Shutdown Mode
♦ Clickless Transitions Into and Out of Shutdown
♦ 1A Current Limit and Thermal Protection
♦ Available in Space-Saving Packages
16-Pin QSOP or Narrow SO
The MAX4295 reduces the number of required external
components. Internal high-speed power-MOS transis-
tors allow operation as a bridge-tied load (BTL) amplifi-
er. The BTL configuration eliminates the need for
isolation capacitors on the output. The frequency-selec-
table pulse-width modulator (PWM) allows the user to
optimize the size and cost of the output filter.
Ordering Information
The MAX4295 is offered in a space-saving 16-pin
QSOP or narrow SO package.
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
MAX4295EEE
MAX4295ESE
Applications
16 Narrow SO
Palmtop/Notebook
Computers
Boom Boxes
AC Amplifiers
PDA Audio
Battery-Powered Speakers
Cordless Phones
Portable Equipment
Pin Configuration appears at end of data sheet.
Sound Cards
Game Cards
Typical Operating Circuit
R
F
AOUT
IN
OUT+
OUT-
C
IN
R
IN
AUDIO
INPUT
MAX4295
V
2.7V TO 5.5V
PV
CC
CC
2.7V TO 5.5V
PV
CC
GND
GND
PGND
PGND
VCM
ON
SHDN
OFF
SS
FS1
FS2
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
ABSOLUTE MAXIMUM RATINGS
V
, PV
to GND or PGND....................................-0.3V to +6V
Continuous Power Dissipation (T = +70°C)
A
CC
CC
PGND to GND..................................................................... 0.3V
PV to V ....................................................................... 0.3V
16-Pin QSOP (derate 8.30mW/°C above +70°C)........667mW
16-Pin Narrow SO (derate 8.7mW/°C above +70°C)......696mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
CC
CC
VCM, SS, AOUT, IN to GND.......................-0.3V to (V
+ 0.3V)
CC
SHDN, FS1, FS2 to GND ..........................................-0.3V to +6V
OUT_ to PGND.........................................-0.3V to (PV
Op Amp Output Short-Circuit
+ 0.3V)
CC
Duration (AOUT).........Indefinite Short Circuit to Either Supply
H-Bridge Short-Circuit
Duration (OUT_) ................Continuous Short Circuit to PGND,
PV
or between OUT+ and OUT-
CC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= PV
= +5V, SHDN = V , FS1 = GND, FS2 = V
(f
= 250kHz), input amplifier gain = -1V/V, T = T
to T , unless
MAX
CC
CC
CC
CC OSC
A
MIN
otherwise noted. Typical values are T = +25°C.) (Note 1)
A
PARAMETER
GENERAL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
(Note 2)
2.7
5.5
4
V
Quiescent Supply Current
Output load not connected
2.8
1.5
mA
Shutdown Supply Current
SHDN = GND
8
µA
0.285 × 0.3 × 0.315 ×
Voltage at VCM Pin
V
V
V
V
CC
CC
CC
FS1 = GND, FS2 = GND
105
210
420
840
125
250
145
290
FS1 = GND, FS2 = V
CC
PWM Frequency
kHz
FS1 = V , FS2 = GND
500
580
CC
FS1 = V , FS2 = V
1000
1160
CC
CC
PWM Frequency Change with
V
= 2.7V to 5.5V
1
3
kHz/V
%
CC
V
CC
V
V
V
V
= 0.06 × V
= 0.30 × V
= 0.54 × V
10.2
49.2
86.2
12
50
13.8
50.8
89.8
0.15
0.5
IN
IN
IN
IN
CC
CC
CC
Duty Cycle
88
Duty Cycle Change with V
= 0.3 × V , V = 2.7V to 5.5V
0.02
0.25
0.35
0
%/V
CC
CC CC
V
V
= 5V
CC
CC
Switch On-Resistance
(each power device)
I
= 150mA
Ω
OUT
= 2.7V
1.0
H-Bridge Output Leakage
H-Bridge Current Limit
SHDN = GND
5
µA
A
1
Soft-Start Capacitor Charging
Current
V
= 0V
0.75
1.8
1.35
1.95
2.6
µA
SS
Undervoltage Lockout
2.2
V
Thermal Shutdown Trip Point
145
°C
2
_______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
= PV
= +5V, SHDN = V , FS1 = GND, FS2 = V
(f
= 250kHz), input amplifier gain = -1V/V, T = T
to T , unless
MAX
CC
CC
CC
CC OSC
A
MIN
otherwise noted. Typical values are T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
0 to 0.6
x V
MAX
UNITS
Input Voltage Range
V
CC
R = 8Ω
0.4
L
V
V
= +3V, f = 1kHz
IN
CC
CC
R = 4Ω
L
0.7
1.2
2
Maximum Output Power
W
R = 8Ω
L
= +5V, f = 1kHz
IN
R = 4Ω
L
Total Harmonic Distortion Plus
Noise
R = 4Ω, f = 1kHz, P = 1W, f = 125kHz
OSC
0.4
87
%
%
L
IN
O
Efficiency
MAX4295, R = 4Ω, f = 1kHz, P = 2W
L
IN
O
LOGIC INPUTS (SHDN, FS1, FS2)
Logic Input Current
V
= 0 to V
1
100
nA
V
LOGIC
CC
0.7 ×
Logic Input High Voltage
V
CC
0.3 ×
Logic Input Low Voltage
V
V
CC
INPUT AMPLIFIER
Input Offset Voltage
0.5
5
4
mV
µV/°C
nA
V
Temp Coefficient
OS
Input Bias Current
(Note 3)
0.05
32
25
Input Noise-Voltage Density
Input Capacitance
f = 10kHz
nV/√Hz
pF
2.5
0.01
Output Resistance
Ω
AOUT Disabled Mode Leakage
Current
SHDN = GND, V
= 0 to V
0.1
1
µA
AOUT
CC
AOUT to GND
8
Short-Circuit Current
mA
dB
AOUT to V
65
CC
Large-Signal Voltage Gain
AOUT Voltage Swing
V
= 0.2V to 4.6V, R
= 10kΩ
78
66
115
40
OUT
L(OPAMP)
V
V
- V
250
100
CC
OL
OH
V
≥ 10mV,
DIFF
mV
R
= 10kΩ
L(OPAMP)
40
Gain-Bandwidth Product
Power-Supply Rejection
Maximum Capacitive Load
1.25
90
MHz
dB
V
= +2.7V to +5.5V
CC
No sustained oscillations
200
pF
Note 1: All devices are 100% production tested at T = 25°C. All temperature limits are guaranteed by design.
A
Note 2: Supply Voltage Range guaranteed by PSRR of input amplifier, frequency, duty cycle, and H-bridge on-resistance.
Note 3: Guaranteed by design, not production tested.
_______________________________________________________________________________________
3
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Typical Operating Characteristics
(V = PV
= +3V, input amplifier gain = -1, SHDN = V , T = +25°C, unless otherwise noted.)
CC A
CC
CC
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 2.5V
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 2.5V
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 2.5V
)
P-P
IN
)
P-P
)
P-P
IN
IN
10
1
10
1
10
1
V
= +5V
CC
V
= +5V
V
= +5V
CC
L
CC
R = 8Ω
L
R = 4Ω
L
R = 32Ω
1MHz
125kHz
125kHz
1MHz
1MHz
125kHz
250kHz
500kHz
0.1
0.01
0.1
0.01
0.1
0.01
500kHz
250kHz
500kHz
250kHz
10
1k
INPUT FREQUENCY (Hz)
100k
10
1k
INPUT FREQUENCY (Hz)
100k
10
1k
INPUT FREQUENCY (Hz)
100k
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (f = 1kHz)
vs. OUTPUT POWER (f = 1kHz)
vs. OUTPUT POWER (f = 1kHz)
IN
IN
IN
100
10
1
100
10
1
100
10
1
V
= +5V
V
= +5V
CC
CC
V
= +5V
CC
R = 32Ω
L
R = 4Ω
L
R = 8Ω
L
1MHz
500kHz
125kHz
1MHz
250kHz
1MHz
250kHz
125kHz
500kHz
0.1
0.1
0.1
250kHz
1.2
500kHz
0.9
125kHz
0.10
0.10
0.10
0
0.1
0.2
0.3
0.4
0.5
0
0.5
1.0
1.5
2.0
2.5
0
0.3
0.6
1.5
1.8
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (f = 20kHz)
vs. OUTPUT POWER (f = 20kHz)
vs. OUTPUT POWER (f = 20kHz)
IN
IN
IN
100
10
1
100
10
1
10
V
= +5V
V
= +5V
CC
L
V
= +5V
CC
L
CC
R = 4Ω
R = 32Ω
R = 8Ω
L
1MHz
1MHz
1
1MHz
125kHz
125kHz
125kHz
250kHz
0.1
0.01
250kHz
500kHz
0.1
0.1
250kHz
1.5
500kHz
500kHz
0.10
0.10
0
0.5
1.0
1.5
2.0
2.5
0
0.1
0.2
0.3
0.4
0.5
0
0.3
0.6
0.9
1.2
1.8
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
4
_______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Typical Operating Characteristics (continued)
(V = PV
= +3V, input amplifier gain = -1, SHDN = V , T = +25°C, unless otherwise noted.)
CC A
CC
CC
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 1.5V
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 1.5V
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT FREQUENCY (V = 1.5V
)
)
)
P-P
IN
P-P
IN
P-P
IN
10
1
10
10
1
V
= +3V
V
= +3V
V
= +3V
CC
CC
CC
R = 8Ω
L
R = 4Ω
L
R = 32Ω
L
1MHz
1MHz
125kHz
500kHz
1MHz
125kHz
125kHz
500kHz
1
0.1
0.01
0.1
0.01
0.1
0.01
250kHz
250kHz
500kHz
250kHz
10
1k
INPUT FREQUENCY (Hz)
100k
10
1k
INPUT FREQUENCY (Hz)
100k
10
1k
INPUT FREQUENCY (Hz)
100k
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (f = 1kHz)
vs. OUTPUT POWER (f = 1kHz)
vs. OUTPUT POWER (f = 1kHz)
IN
IN
IN
100
10
1
100
10
1
100
10
1
V
= +3V
V
= +3V
CC
CC
V
= +3V
CC
R = 4Ω
L
R = 8Ω
L
R = 32Ω
L
1MHz
1MHz
1MHz
500kHz
500kHz
250kHz
125kHz
500kHz
125kHz
250kHz
0.1
0.1
250kHz
125kHz
0.1
0.10
0.10
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
OUTPUT POWER (W)
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
OUTPUT POWER (W)
0
0.05
0.10
0.15
0.20
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (f = 20kHz)
IN
vs. OUTPUT POWER (f = 20kHz)
vs. OUTPUT POWER (f = 20kHz)
IN
IN
100
10
1
100
10
1
100
10
1
V
= +3V
V
= +3V
V
= +3V
CC
CC
L
CC
R = 4Ω
L
R = 8Ω
R = 32Ω
L
1MHz
1MHz
1MHz
250kHz
125kHz
125kHz
500kHz
500kHz
250kHz
0.1
0.1
0.1
125kHz
250kHz
500kHz
0.10
0.10
0.10
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
OUTPUT POWER (W)
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
OUTPUT POWER (W)
0
0.05
0.10
0.15
0.20
OUTPUT POWER (W)
_______________________________________________________________________________________
5
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Typical Operating Characteristics (continued)
(V = PV
CC
= +3V, input amplifier gain = -1, SHDN = V , T = +25°C, unless otherwise noted.)
CC A
CC
EFFICIENCY
vs. OUTPUT POWER (f = 1kHz)
EFFICIENCY
vs. OUTPUT POWER (f = 1kHz)
EFFICIENCY
vs. OUTPUT POWER (f = 1kHz)
IN
IN
IN
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
250kHz
500kHz
500kHz
250kHz
1MHz
250kHz
1MHz
500kHz
1MHz
125kHz
125kHz
125kHz
V
= +5V
V
CC
= +5V
CC
V
= +5V
CC
R = 4Ω
R = 32Ω
L
L
R = 8Ω
L
0
0
0.5
2.5
0
0.3
0.6
0.9
1.2
1.5
1.8
0
0.1
0.2
0.3
0.4
0.5
1.0
1.5
2.0
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
EFFICIENCY
EFFICIENCY
vs. OUTPUT POWER (f = 1kHz)
vs. OUTPUT POWER (f = 1kHz)
IN
IN
100
90
80
70
60
50
40
30
20
10
0
100
500kHz
500kHz
90
80
70
60
50
40
30
20
10
0
250kHz
1MHz
250kHz
1MHz
125kHz
125kHz
V
= +3V
CC
V
CC
= +3V
R = 4Ω
L
R = 8Ω
L
0
0.2
0.4
0.6
0.8
0
0.2
0.4
0.6
0.8
OUTPUT POWER (W)
OUTPUT POWER (W)
EFFICIENCY
vs. OUTPUT POWER (f = 1kHz)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
IN
100
90
80
70
60
50
40
30
20
10
0
10
8
A: f
= 125kHz
OSC
OSC
OSC
OSC
250kHz
D
B: f
C: f
D: f
= 250kHz
= 500kHz
= 1MHz
500kHz
1MHz
6
4
C
B
125kHz
2
0
V
= +3V
CC
A
R = 32Ω
L
2
0
0.05
0.10
0.15
0.20
0
1
3
4
5
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
6
_______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Typical Operating Characteristics (continued)
(V = PV
= +3V, input amplifier gain = -1, SHDN = V , T = +25°C, unless otherwise noted.)
CC A
CC
CC
OSCILLATOR FREQUENCY DEVIATION
vs. SUPPLY VOLTAGE
STARTUP/SHUTDOWN
WAVEFORM
MAX4295 toc27
0.015
0.010
0.005
0
125kHz
4V/div
V
OUT
-0.005
-0.010
-0.015
-0.020
-0.025
250kHz
500kHz
R = 4Ω
OSC
2.5V/div
SHDN
L
f
f
= 250kHz
= 10kHz
IN
1MHz
C
SS
= 560pF
2.5
3.0
3.5
4.0
4.5
5.0
5.5
400µs/div
SUPPLY VOLTAGE (V)
Pin Description
PIN
NAME
GND
PV
FUNCTION
1, 12
2, 15
3
Analog Ground
H-Bridge Power Supply
Positive H-Bridge Output
Power Ground
CC
OUT+
PGND
4, 13
5
V
Analog Power Supply
CC
6
VCM
Audio Input Common-Mode Voltage. Do not connect. Minimize parasitic coupling to this pin.
7
8
IN
Audio Input
AOUT
Input Amplifier Output
9
SHDN
Active-Low Shutdown Input. Connect to V
for normal operation. Do not leave floating.
CC
10
11
14
16
FS1
FS2
OUT-
SS
Frequency Select Input 1
Frequency Select Input 2
Negative H-Bridge Output
Soft-Start
_______________________________________________________________________________________
7
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
AOUT
PV
CC
MAX4295
IN
OUT+
GATE
DRIVE
PGND
✕
0.3
V
CC
(VCM)
PV
CC
GATE
DRIVE
OUT-
FS1
FS2
PWM
OSC
V
CC
SS
PGND
POWER MANAGEMENT
AND PROTECTION
GND
CSS
Figure 1. Functional Diagram
mum input frequencies so that intermodulation products
are outside the input signal bandwidth. Higher switching
frequencies also simplify the filtering requirements.
Detailed Description
The MAX4295 switch-mode, Class D audio power
amplifier is intended for portable multimedia and gener-
al-purpose audio applications. Linear amplifiers in the
1W to 2W output range are inefficient; they overheat
when operated near rated output power levels. The effi-
ciency of linear amplifiers is <50% when the output
voltage is equal to 1/2 the supply. The MAX4295 Class
D amplifier achieves efficiencies of 87% or greater and
is capable of delivering up to 2W of continuous maxi-
mum power to a 4Ω load. The lost power is due mainly
to the on-resistance of the power switches and ripple
current in the output.
The MAX4295 consists of an inverting input operational
amplifier, a PWM ramp oscillator, a controller that con-
verts the analog input to a variable pulse-width signal,
and a MOSFET H-bridge power stage (Figure 1). The
control signal is generated by the PWM comparator; its
pulse width is proportional to the input voltage. Ideally
the pulse width varies linearly between 0% for a 0V
input signal and 100% for full-scale input voltages
(Figure 2). This signal controls the H-bridge. The
switches work in pairs to reverse the polarity of the sig-
nal in the load. Break-before-make switching of the H-
bridge MOSFETs by the driver circuit keeps supply
current glitches and crowbar current in the MOSFETs at
a low level. The output swing of the H-bridge is a direct
function of the supply voltage. Varying the oscillator
swing in proportion to the supply voltage maintains
constant gain with varying supply voltage.
In a Class D amplifier, a PWM controller converts the
analog input to a variable pulse-width signal. The pulse
width is proportional to the input voltage, ideally 0% for
a 0V input signal and 100% for full-scale input voltages.
A passive lowpass LC network filters the PWM output
waveform to reconstruct the analog signal. The switch-
ing frequency is selected much higher than the maxi-
8
_______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
bridge transistors. The H-bridge transistors are
enabled after the IC’s junction temperature cools by
10°C. This results in a pulsating output under continu-
ous thermal overload conditions. Junction temperature
does not exceed the thermal overload trip point in nor-
mal operation, but only in the event of fault conditions,
such as when the H-bridge outputs are short circuited.
Undervoltage Lockout
At low supply voltages, the MOSFETs in the H-bridge
V
IN
may have inadequate gate drive thus dissipating
excessive power. The undervoltage lockout circuit pre-
vents the device from operating at supply voltages
below +2.2V.
V
RAMP
Low-Power Shutdown Mode
The MAX4295 has a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low disables the H-bridge, turns off the circuit,
and places the MAX4295 in a low-power shutdown
+5V
V
OUT
0V
Figure 2. PWM Waveforms
mode. Connect SHDN to V
for normal operation.
CC
Applications Information
FS1 and FS2 program the oscillator to a frequency of
125kHz, 250kHz, 500kHz, and 1MHz. The sawtooth
Component Selection
✕
oscillator swings between GND and 0.6
V
. The
CC
Gain Setting
input signal is typically AC-coupled to the internal input
op amp, whose gain can be controlled through exter-
nal feedback components. The common-mode voltage
✕
External feedback components set the gain of the
MAX4295. Resistors R and R set the gain of the
F
IN
input amplifier to -(R /R ). The amplifier’s noninverting
F
IN
of the input amplifier is 0.3
V
and is internally gen-
CC
✕
input is connected to the internally generated 0.3
(VCM) that sets the amplifier’s common-mode voltage.
V
CC
erated from the same resistive divider used to generate
✕
the 0.6
V
reference for the PWM oscillator.
CC
The amplifier’s input bias current is low, 50pA, and
does not affect the choice of feedback resistors. The
Current Limit
A current-limiting circuit in the H-bridge monitors the
current in the H-bridge transistors and disables the H-
bridge if the current in any of the H-bridge transistors
exceeds 1A. The H-bridge is enabled after a period of
100µs. A continuous short circuit at the output results
in a pulsating output.
noise in the circuit increases as the value of R
increases.
F
The optimum impedance seen by the inverting input is
between 5kΩ and 20kΩ. The effective impedance is
✕
given by (R
R )/(R + R ). For values of R >
IN F IN F
F
50kΩ, a small capacitor (≈3pF) connected across R
F
compensates for the pole formed by the input capaci-
Thermal Overload Protection
Thermal overload protection limits total power dissipa-
tion in the MAX4295. When the junction temperature
exceeds +145°C, the thermal detection disables the H-
tance and the effective resistance at the inverting input.
_______________________________________________________________________________________
9
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Soft-Start (Clickless Startup)
The H-bridge is disabled under any of the following
conditions:
Frequency Selection
The MAX4295 has an internal logic-programmable
oscillator controlled by FS1 and FS2 (Table 1). The
oscillator can be programmed to frequencies of
125kHz, 250kHz, 500kHz, and 1MHz. The frequency
should be chosen to best fit the application. As a rule of
• SHDN low
• H-bridge current exceeds the 1A current limit
• Thermal overload
thumb, choose f
to be 10 times the audio band-
OSC
• Undervoltage lockout
width. A lower switching frequency offers higher ampli-
fier efficiency and lower THD but requires larger
external filter components. A higher switching frequen-
cy reduces the size and cost of the filter components at
the expense of THD and efficiency. In most applica-
The circuit re-enters normal operation if none of the
above conditions are present. A soft-start function pre-
vents an audible pop on restart. An external capacitor
connected to SS is charged by an internal 1.2µA cur-
rent source and controls the soft-start rate. V is held
SS
tions, the optimal f
is 250kHz.
OSC
low while the H-bridge is disabled and allowed to ramp
✕
up to begin a soft-start. Until V reaches 0.3
V
,
CC
SS
the H-bridge output is limited to a 50% duty cycle,
independent of the input voltage. The H-bridge duty
cycle is then gradually allowed to track the input signal
at a rate determined by the ramp on SS. The soft-start
✕
Table 1. Frequency Select Logic
FS1
1
FS2
1
FREQUENCY (Hz)
1M
cycle is complete after V reaches 0.6
V
. If the
CC
SS
0
1
500k
250k
125k
soft-start capacitor is omitted, the device starts up in
approximately 100µs.
1
0
0
0
Input Filter
High-fidelity audio applications require gain flatness
between 20Hz to 20kHz. Set the low-frequency cutoff
point with an AC-coupling capacitor in series with the
input resistor of the amplifier, creating a highpass filter
(Figure 3). Assuming the input node of the amplifier is a
virtual ground, the -3dB point of the highpass filter is
R
F
AOUT
C
IN
INPUT
R
IN
IN
✕
✕
determined by: f
= 1/(2π
R
C ), where R is
IN IN
IN
LO
the input resistor, and C is the AC-coupling capaci-
IN
tor. Choose R as described in the Gain Setting sec-
IN
VCM
tion. Choose C such that the corner frequency is
IN
below 20Hz.
Figure 3. Input Amplifier Configuration
10 ______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
• Balanced 2-Pole (Figure 4b):
Output Filter
A balanced 2-pole filter does not have the common-
mode swing problem of the single-ended filter.
An output filter is required to attenuate the PWM switch-
ing frequency. Without the filter, the ripple in the load
can substantially degrade efficiency and may cause
interference problems with other electronic equipment.
✕
✕
✕
✕
C = 2 / (√2
R
L
ω ), L = (√2 R )/(2 ω ); choosing
o L o
f = 30kHz and R = 4Ω, C1a = C1b = 2.0µF, L1a =
L1b = 15µH.
o
L
A Butterworth lowpass filter is chosen for its flat
passband and nice phase response, though other filter
implementations may also be used. Three examples
are presented below. The filter parameters for bal-
anced 2-pole (Figure 4b) and 4-pole (Figure 4d)
Butterworth filters are taken from Electronic Filter
Design Handbook by Arthur B. Williams, McGraw Hill,
Inc. These filter designs assume that the load is purely
resistive and load impedance is constant over frequen-
cy. Calculation of filter component values should
include the DC resistance of the inductors and take into
account the worst-case load scenario:
A single capacitor connected across R , with a value of
L
✕
✕
C = 1/(√2
L
R
ω ), can be used in place of C1a and
L
o
C1b. However, the configuration as shown gives an
improved rejection to common-mode signal compo-
nents of OUT+_ and OUT-_. If the single capacitor
scheme is used, additional capacitors (Ca and Cb) can
be added from each side of R , providing a high-fre-
L
quency short to ground (Figure 4c). These capacitors
✕
should be approximately 0.2 C .
L
• Balanced 4-Pole Filter (Figure 4d)
A balanced 4-pole filter is more effective in suppress-
ing the switching frequency and its harmonics.
• Single Ended 2-Pole Filter (Figure 4a)
✕
✕
✕
C = 1 / (√2
R
f
ω ), L = √2 R / ω
o L o
L
For the 4-pole Butterworth filter, the normalized values
✕
✕
where ω = 2
π
(f = filter cutoff frequency);
o
o
o
are: L1 = 1.5307, L2 = 1.0824, C1 = 1.5772, C2 =
N
N
N
N
choosing f = 30kHz and R = 4Ω, C = 0.937µF, L =
o
L
0.3827.
30µH.
The actual inductance and capacitance values for f
=
O
A single-ended 2-pole filter uses the minimum number
of external components, but the load (speaker) sees
the large common-mode switching voltage, which can
increase power dissipation and cause EMI problems.
30kHz and a bridge-tied load of R = 4Ω are given by:
L
✕
✕
✕
L1 = (L1
R ) / (2 ω ) = 16.24µH, L2 = (L2
R ) /
L
N
L
o
N
✕
✕
(2 ω ) = 11.5µH, C1 = C1 / (R
ω ) = 2.1µF, C2a =
o
N
L
o
✕
✕
C2b = (2 C2 ) / (R
N
ω ) = 1.0µF.
o
L
L1
L
OUT+
OUT-
OUT+
Ca
Cb
C
L
R
L
R
L
C
OUT-
L2
Figure 4c. Alternate Balanced 2-Pole Filter
Figure 4a. Single-Ended 2-Pole Filter
L2a
L1a
L1
OUT+
OUT+
C2a
C2b
C1a
C1b
C1
R
R
L
L
OUT-
OUT-
L1b
L2b
L2
Figure 4d. Balanced 4-Pole Filter
Figure 4b. Balanced 2-Pole Filter
______________________________________________________________________________________ 11
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Filter Components
Total Harmonic Distortion
The MAX4295 exhibits typical THD+N of <1% for input
frequencies <10kHz. The PWM frequency affects THD
performance. THD can be reduced by limiting the input
bandwidth through the input highpass filter, choosing
The inductor current rating should be higher than the
peak current for a given output power requirement and
should have relatively constant inductance over tem-
perature and frequency. Typically, an open-core induc-
tor is desirable since these types of inductors are more
linear. Toroidal inductors without an air gap are not rec-
ommended. Q-shielded inductors may be required if
the amplifier is placed in an EMI-sensitive system. The
series resistance of the inductors will reduce the atten-
uation of the switching frequency and reduce efficiency
due to the ripple current in the inductor.
the lowest f
possible, and carefully selecting the
OSC
output filter and its components.
Bypassing and Layout Considerations
Distortion caused by supply ripple due to H-bridge
switching can be reduced through proper bypassing of
PV . For optimal performance, a 330µF, low-ESR
CC
POSCAP capacitor to PGND and a 1µF ceramic capac-
The capacitors should have a voltage rating 2 to 3
times the maximum expected RMS voltage—allowing
for high peak voltages and transient spikes—and be
stable over temperature. Good quality capacitors with
low equivalent series resistance (ESR) and equivalent
series inductance (ESL) are necessary to achieve opti-
mum performance. Low-ESR capacitors will decrease
power dissipation. High ESL will shift the cutoff frequen-
cy, and high ESR will reduce filter rolloff.
itor to GND at each PV
input is suggested. Place the
CC
1µF capacitor close to the PV
pin. Bypass V
with
CC
CC
a 10µF capacitor in parallel with a 1µF capacitor to
GND. Ceramic capacitors are recommended due to
their low ESR.
Good PC board layout techniques optimize perfor-
mance by decreasing the amount of stray capacitance
at the amplifier’s inputs and outputs. To decrease stray
capacitance, minimize trace lengths by placing exter-
nal components as close as possible to the amplifier.
Surface-mount components are recommended.
Bridge-Tied Load/Single-Ended
Configuration
The MAX4295 can be used as either a BTL or single-
ended configured amplifier. The BTL configuration offers
several advantages over a single-ended configuration.
By driving the load differentially, the output voltage swing
is doubled and the output power is quadrupled in com-
parison to a single-ended configuration. Because the dif-
ferential outputs are biased at half supply, there is no DC
voltage across the load, eliminating the need for large
DC-blocking capacitors at the output.
The MAX4295 requires two separate ground planes to
prevent switching noise from the MOSFETs in the H-
bridge from coupling into the rest of the circuit. PGND,
the power ground, is utilized by the H-bridge and any
external output components, while GND is used by the
rest of the circuit. Connect the PGND and GND planes
at only one point, as close to the power supply as pos-
sible. Any external components associated with the
output of the MAX4295 must be connected to the
PGND plane where applicable. Use the Typical
Operating Circuit diagram as a reference. Refer to the
evaluation kit manual for suggested component values,
component suppliers, and layout.
The MAX4295 can be configured as a single-ended
amplifier. In such a case, the load must be capacitively
coupled to the filter to block the half-supply DC voltage
from the load. The unused output pin must also be left
open (Figure 5). Do not connect the unused output pin
to ground.
C
c
L1a
1
OUT+
OUT-
C1
R
L
MAX4295
16
Figure 5. MAX4295 Single-Ended Configuration
12 ______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Pin Configuration
Chip Information
TRANSISTOR COUNT: 846
PROCESS: BiCMOS
TOP VIEW
GND
1
2
3
4
5
6
7
8
16 SS
15 PV
PV
CC
CC
OUT+
14 OUT-
13 PGND
12 GND
11 FS2
PGND
MAX4295
V
CC
VCM
IN
10 FS1
AOUT
9
SHDN
SO/QSOP
______________________________________________________________________________________ 13
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
1
21-0055
E
1
14 ______________________________________________________________________________________
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
INCHES
MILLIMETERS
DIM
A
MIN
MAX
0.069
0.010
0.019
0.010
MIN
1.35
0.10
0.35
0.19
MAX
1.75
0.25
0.49
0.25
0.053
0.004
0.014
0.007
N
A1
B
C
e
0.050 BSC
1.27 BSC
E
0.150
0.228
0.016
0.157
0.244
0.050
3.80
5.80
0.40
4.00
6.20
1.27
E
H
H
L
VARIATIONS:
INCHES
1
MILLIMETERS
DIM
D
MIN
MAX
0.197
0.344
0.394
MIN
4.80
8.55
9.80
MAX
5.00
N
8
MS012
AA
TOP VIEW
0.189
0.337
0.386
D
8.75 14
10.00 16
AB
D
AC
D
C
A
B
0∞-8∞
e
A1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0041
B
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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