LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
Copyright 2000
Rev. 1.1, 2000-12-01
A MICROSEMI COMPANY
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
Copyright 2000
Rev. 1.1, 2000-12-01
INTRODUCING LX1710/1711 AUDIOMAX
Thank you for your interest in the latest generation of AudioMAX products. The enclosed LXE1710 evaluation
board is a fully functional mono amplifier designed to demonstrate the “new and improved” Switching Class-D
Power Amplifier IC from Linfinity Microsemi. The LX1710/1711 is a completely new controller design with
superior performance over the LX1720 stereo controller IC. Key improvements include better SNR, lower noise
floor, and reduced THD therefore resulting in a much “quieter” and “cleaner” sounding amplifier.
The evaluation board has been configured w ith easy -to- use term inal block connections for power supply/battery hook
up and speaker connections. An RCA jack or separate audio +/- pins allow a quick interface to your audio source.
Jumpers are also provided to enable/disable the amplifier (Sleep control) and to turn off the audio input (Mute
control). With minimal setup, the user can be listening to the amplifier in a matter of a few minutes.
Both the LX1710 and LX1711 operate from a single supply voltage. The LXE1710 evaluation board can
!
e
LX1711 can handle a higher supply voltage (7V to 25V) and provides greater than 50W continuous output power
! " " ! "
change frequency response for other load optimization.
Thank you again for your interest in the new “quieter”, high efficiency Class-D Audio Amplifier from Linfinity
Microsemi. Please let us know what you think and stay tuned for future product releases to our AudioMAX family
of products.
Regards,
Linfinity Microsem i
http://www.linfinity.com
(714) 898-8121
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
Copyright 2000
Rev. 1.1, 2000-12-01
TABLE OF CONTENTS
LX1710 / 1710 AudioMAX Evaluation Board Feat ures and Ci rcui t Description .............................4
Input Compensation
Output Stage
Filter Stage
Quick Start Guide............................................................................................................................................5
Application Schematic...................................................................................................................................6
Electrical Characteristics..............................................................................................................................7
Performance Graphs......................................................................................................................................8
Application I nformat i on
Filter Design Tradeoffs (1-Stage vs. 2-Stage).............................................................................................9
LC Filter Design...........................................................................................................................................9
MOSFET Selection....................................................................................................................................10
Inductor Selection......................................................................................................................................12
Capacitor Selection ...................................................................................................................................13
Gate Resistor ............................................................................................................................................14
Oscillator Configuration.............................................................................................................................14
Multi Channel Requirements and Frequency Synchronization..................................................................14
PCB Layout ...............................................................................................................................................15
Board Layout..................................................................................................................................................16
Printed Circui t Board ................................................................................................................................... 17
Bill of Materials..............................................................................................................................................18
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
Copyright 2000
Rev. 1.1, 2000-12-01
Part Number Product Description
LX1710CDB AudioMAX High
Fidelity Controller IC VDD = 7V to 15V, Switching Class-D Mono
Power Amplifier IC, 28-Pin SSOP Package.
LX1711CDB AudioMAX High
Power Controller IC VDD = 7V to 25V, Switching Class-D Mono
Power Amplifier IC, 28-Pin SSOP Package.
LXE1710 LX1710 AudioMAX
Evaluation Board Fully Operational Mono Audio Amplifier.
LX1710/1711 AUDIOM AX EVALUATION BOARD FEATURES AND CIRCUIT DESCRIPTION
• Fully Assembled Mono Evaluation Board with
LX1710 Class-D Controller IC
• Improved SNR and Noise Floor Performance
• Output Power of 25W typical (LX1710, 15VDD,
• Output Power of 54W typical (LX1711, 25VDD,
• Supports Full Audio Bandwidth
•
• Terminal Block Connectors for Supply
Voltage and Speaker Connection
• RCA Plug for Audio Input Signal
The AudioMAX Evaluation Amplifier Board allows the
user to quickly connect and evaluate the LX1710
Switching Class-D Mono Controller IC. Easy-to-
connect terminal blocks and an RCA plug are
provided for inter facing to Power, Speaker , and Audio
Input connections. The single stage output filter has
been configured to drive a 4
audio bandwidth amplification (See Application
section LC filter design for component selection,
calculations, and suggested inductor and capacitor
values for other loads). The LXE1710 Evaluation
Board operates from a single supply voltage.
The Class-D Amplifier Controller IC requires a
minimal number of external components to create a
com plete amplif ier solution. See LXE1710 Evaluation
Board Schematic and Bill of Materials for circuit
specifics. A Class-D Amplifier is a “switching”
amplifier that converts a low-level, analog audio input
signal into a high power, pulse-width modulated
(PWM) output. The switching frequency (500kHz
typical but can be adjusted) is much higher than the
audio bandwidth (20Hz to 20kHz), and is easily
filtered out with a simple LC filter. The support
circuitry can be generally grouped into three areas
(input circuit, output power stage, and output filter).
INPUT COMPENSATION
The first group is the compensation network and
control setting components. These resistors and
capacitors set up the controller operating frequency,
response characteristics, and comparator ramp
fundamental to Class-D operation.
OUTPUT STAGE
The next section is the output stage. The controller
IC generates a PWM output by controlling external
FETs connec ted in a f ull br idge c onf iguration. The f ull
bridge configuration is connected between the single
supply voltage (PVDD) and ground (PGND) with the
output of the bridge driving the LC filter stage.
Because the FETs are either fully “on” or fully “off”,
Class-D topology is extremely efficient (up to 85%
typical), circuit power dissipation is minimal, and
maximum power is delivered to the speaker. The
bridge output also drives the RC low pass filter, which
provides the f eedback for the control loop through the
FBK+ and FBK- inputs.
FILTER STAGE
The single stage, second order LC filter is used to
remove the switching frequency. The frequency
response and corner frequency can be easily
adjusted for optimization of various loads. The LC
evaluation board component values have been
chosen for a 4
! " # $
for component selection.
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
Copyright 2000
Rev. 1.1, 2000-12-01
QUICK START GUIDE
The LXE1710 Evaluation Board is a fully functional,
Class-D Amplifier. Connection to a single supply
voltage (VDD from either a battery or power supply),
speakers, and your audio source is all that is required
to begin evaluating the amplif ier and listening to music .
The following outlines the necessary connections and
control jumpers.
1) Verify contents of Evaluation Kit: The easy-to-
use am plifier is all c ontained on a single board.
Visually inspect to see if the board or any
components were damaged during shipping.
All components are located on the top side of
the PCB except for the decoupling capacitor,
C17. A copy of the LX1710/1711 Datasheet
should also be enclosed or a PDF version can
be downloaded from the Microsemi.com
website
(http://www.microsemi.com/datasheets/MSC1580.PDF).
2) Power and Ground Connections: The voltage
supply and ground connections are made
through terminal block TB1. Connect your “+”
(+7V to +15V) power supply or battery to the
+V input of TB1. Connect your supply or
battery ground to the GND input of TB1.
Please ensure the correct positive and ground
connections are made before turning on the
power supply.
3) Speaker Connection: The amplifier is designed
$ ! #"
“+” and “-“ to the +OUT and –OUT input of
terminal block TB2 respectively. The amplifier
can be used to drive other speaker loads but
frequency response may not be optimal. See
LC filter design section for recommended
inductor and capacitor modifications.
4) Audio Input Connection: Connect your audio
source to the RCA Jack CN1, Audio In. For
other type interfaces, the audio input signal c an
also be connected to the amplifier board using
the J3 (In- and In+) location. Strip Line Plugs
can be inserted into J3 for connectivity.
5) Jumper Selection Controls: The “on/off” or
enable to the module is controlled with the
SLEEP/ signal. Jumper J1 connects the
SLEEP/ to “on” or “ off”. SLEEP/ is an active
Low control. Jumper J2 connects the MUTE
control which enables/disables the audio input
to the amplif ier . MUT E is an ac tive High s ignal.
See table below.
6) Power Source: If a power supply is being used,
make sure it is set to the correct voltage level
and turn the power supply on.
7) Audio Source: Make sure the audio source
signal is se t to a minim um level. Start or “play”
audio source and adjust source volume to
desired level.
8) Listen to AudioMAX: If the amplifier is not
operating properly, verify preceding steps or
contact Linfinity for technical assistance (714)
898-8121.
Jumper
toward
OFF
Jumper
toward
ON
Jumper
floating
J1 Jumper:
SLEEP/
Amplifier
enabled
(SLEEP/ is
OFF)
Amplifier
disabled
(SLEEP/ is
ON)
Amplifier
disabled
(SLEEP/ is
ON)
J2 Jumper:
MUTE
Audio Input
enabled
(MUTE is
OFF)
Audio Input
disabled
(MUTE is ON)
Audio Input
enabled
(MUTE is
OFF)
Jumper Settings
To Power Supply +V
7V-15V for LX1710
7V-25V for LX1711
To Speaker + To Speaker -
To Power Supply
Ground
Optional
Audio In -
Optional
Audio In +
To Audio
Source
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
Copyright 2000
Rev. 1.1, 2000-12-01
SCHEMATIC
VDD
PVDD
CP
RPWM
CPWM
VREF
V25
GND
SLEEP
MUTE
INAMPOUT
INPUT+
INPUT-
EAOUT
EAIN
FAOUT STATUS
CLOCK
P+
PGND
CN
FBK+
FBK-
N+
P-
N-
IS-
R5 34.8K
R1 56.2K
R2 10K
C11
4.7µF
C3
470nF
C14
470nF
C4
150pF
C5
18pF
R8 10K
R9 10K
C26
330pF
C2
1µF
C1
1µF
C16
100pF
MUTE
SLEEP
VIN7V to 15V
C22
.1µF
R11
10 ohm
R6
10 ohm
R10
10 ohm
R12
10 ohm
Q3
Q2
Q4
C8
.1µF
50V
RS1
.0347
C17
220µF
25V
Q1
C12
.1µF
C10
4.7µF
R13
15 ohm
1W
L1 15µH
L2 15µH
C20
.68µF
C21
.68µF C19
.47µF
C18
.47µF
R3
24.3K
C7
220pF
R4
24.3K
C6
220pF
LX1710
NC
NC
AUDIO
INPUT
NC
25
24
26
5
6
1
4
2
10
11
9
7
8
14
13
15
28
27
23
22
20
21
19
18
16
17
12
NC
3
C9
0.1µF
35V
C13
2.2µF +
+
+
+
– Evaluation Board Schematic
LXE 1710 EVALUATION BOARD U
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Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
Copyright 2000
Rev. 1.1, 2000-12-01
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C<TA<70°C.
For test circuit, see LXE1710 Evaluation Board Schematic diagram.
PARAMETER SYMBOL TEST CONDITIONS MIN. TYP. MAX UNITS
Supply Voltage LX1710 VDD 7 15 V
Supply Current IDD VIN=15V, PO=38W, RL
THD+N=1% 3 A
Quiescent Current IQ V IN=15V, No Input 43 mA
VIN=15V, RL
10Hz to 22kHz 14 W
VIN=15V, RL
10Hz to 22kHz 25 W
Output Power PO
VIN=15V, RL
10Hz to 22kHz 38 W
VIN=15V, fIN=1kHz, PO=10W 82 %
Efficiency
VIN=15V, fIN=1kHz, PO=20W 85 %
fIN=1kHz, PO=1W 0.05 %
Total Harmonic Dis tortion Plus
Noise THD+N fIN=20Hz to 20kHz, PO=1W 0.3 %
Signal-To-Noise Ratio SNR 81 dBV
Power Supply Rejec tion Ratio PSRR VIN=15V, VRIPPLE=1VRMS,
10Hz to 10kHz -70 dB
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
Copyright 2000
Rev. 1.1, 2000-12-01
PERFORMANCE GRAPHS
45%
50%
55%
60%
65%
70%
75%
80%
85%
90%
0 5 10 15 20 25 30
Output Power (W)
Efficency (%)
0
10
20
30
40
50
60
611162126
Supply Voltage ( VIN)
Output Power (W)
VIN = 15V fIN=1kHz
RL
%
THD+N=1%
-20
+20
-15
-10
-5
+
5
+10
+15
-0.08
-0.59
Voltage A mplifica tion (dBr)
10 80k
50 100 200 500 1k 2k 5k 10k 50k
17.88k
18.2 Frequency (Hz)
0.001
100
0.002
0.005
0.01
0.02
0.1
0.5
1
2
5
10
20
50
0.26
0.04
THD + N (%)
50m 30
100m 200m 500m 2 5 10 20 24.56
1.13
Output Powe r (W)
VIN=15V
RL
%
RO=1WRMS
VIN=15V
fIN=1kHz
RL
%
LXE 1710 EVALUATION BOARD U
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Microsemi
Linfini ty Microelectronics Di vi sion
11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
Copyright 2000
Rev. 1.1, 2000-12-01
APPLICATION INFORMATION
! &' (
LX1710 Filter Implementation, 1-stage vs. 2- stage
0.001
100
0.002
0.005
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
10
20
50
0.55626
0.12572
Percent (%)
50m 30
100m 200m 500m 1 2 5 10 20
25.04
1.15
Watts(W)
2-Stage
1-Stage
FILTER DESIGN TRADEOFFS (1-STAGE VS. 2-STAGE)
A 1-stage or 2-stage filter may be used depending on
your application and performance targets. The main
tradeoff in this selection is price (number of
components, component costs, PCB area) vs.
performance. The primary advantage of the single
stage f ilter is lower cost whereas the m ain benefit to a
2-stage filter is that it will provide steeper attenuation.
This allows the c orner frequency to be selected f urther
outside of the audio band (to minimize the effects of
impedance variations in the passband) and still
provide adequate RF attenuation.
Single Stage Filter Advantages
• Low Cost: The 1-stage LC filter uses one half
the number of inductors/c apacitors resulting in
a substantial cost savings over a 2-stage
design. Key parameters such as THD+N,
frequency response, and nose performance
do not change significantly.
• Power Loss: Since current will flow in two
inductors and not f our, the inductor power loss
will be less in the single stage design. The
overall amplifier will have a wider dynamic
range and improved efficiency.
• Filter Design: This easy-to-design filter can
limit audio signal changes within +/- 3dB
across the audio band with impedance
vari
" ) *+ ,!
a steeper rolloff with the 2-stage filter,
impedance changes could result in a +/- 6dB
change.
• THD: There are minimal differences between
the 1-stage and 2-stage implementations with
other parameters such as THD+N as seen in
the above graph.
Single Stage Filter Disadvantages
• EMI and Switching Frequency: For the 1-
stage, the switching frequency must be higher
than 400kHz to ensure the corner frequency
will provide adequate amplifier performance in
the high end of the audio frequency range. If
fS < 400kHz, then fC < fS /10 = 40kHz which is
too close to the desired audio band. A higher
oscillation frequency could translate into
greater MOSFET switching losses, slightly
lower efficiency, and increased EMI effects.
With a 2-stage 4th order filter, the switching
frequency fS can be reduced to 120kHz. If fS =
120kHz, then fC = fS /3 = 40kHz. The lower
oscillation frequency could help minimize EMI
issues.
LC FILTER DESIGN
The output filter helps to reconstruct the amplified
audio signal and filter out the switching frequency.
The design of the filter depends on the type of
attenuation and frequency response desired at the
output. The output filter designed into the LXE1710
LXE 1710 EVALUATION BOARD U
SER GUIDE
Microsemi
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11861 Western A venue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
Copyright 2000
Rev. 1.1, 2000-12-01
evaluation board is a second order, LC type filter as
shown below. Tradeoffs between performance and
com ponent cost m ust be cons idered when determining
the complexity or type of filter selected.
OUT+
OUT-
L 15µH
L 15µH
C
0.68µF
C
0.68µF
R
Its Laplace Transform function is:
ω
ω
ω
ω
RCQ
LC
S
Q
S
C
S
LC
S
RC
S
C
S
=
=
++
=
++
=
1
Where
11
H(S) 222
The Class-D amplifier evaluation board design has a
pass-band of 20Hz to 20kHz to support the audio
frequenc y range and is configured to utilize a switching
or oscillator frequency fs = 500kHz. Depending on the
application, this oscillator frequency may be adjusted
(see section on Oscillator Configuration) to optimize
amplifier performance or modified for other
considerations such as EMI effects. Further
requirements of the filter are that the pass band
attenuation of switching frequency fs should be lower
than 40dB and the corner frequency of the LC filter
should be set higher than 20kHz to avoid attenuating
audio signals in the desired audio band by more than
1dB. A speaker DC impedance o
'-
C =
50kHz corner frequency are defined for the evaluation
board.
The Q (selectivity factor or ratio of the center
frequency divided by the bandwidth) of the filter must
also be consider ed when designing a filter . Too high a
Q will result in a boost of the audio signal across the
audio band whereas a low Q will cause too much
attenuation of the signal. A Q value of 0.707 provides
the required audio response and is used in the
calculation below.
Board Evaluation in the used is µF68.0
µ56.0
)50000)(2(4 707.0
)f2(
=
====
C
F
RQ
R
Q
CC
ππω
To Compute the Inductor Value:
Board Evaluation in the used is µH15
µ9.14
)µ68(.)]50000)(2[(
1
)f2(
11 222
=
====
L
H
CC
LC
ππω
LXE1710 Evaluation Board
Frequency Response
-15
+15
-12.5
-10
-7.5
-5
-2.5
+0
+2.5
+5
+7.5
+10
+12.5
Voltage Am plif icati on (dBr)
10 80
k
20 50 10 20 50 1
k
2k 5k 10
k
20
k
50
k
Frequency (Hz)
Frequency response of the audio amplifier was
$ " )
,! - $- + - -
"" ' . ! - ,
) " + )/ .
–4dB
attenuation respectively. Therefore, to improve
frequency response performance for other loads, the
value of Q must be increased/decreased by changing
the capacitor. Since a different value C will affect the
corner frequency, values for L and C must be
recalculated. Below are recommended inductor and
capacitor values for 2
, -
single stage LC filter design.
Capacitor C (µF) Inductor L (µH)
1.0 10
0.68 15
0.47 22
Filter Component Values
Please note: These recommended values are guidelines
for speaker loads. Actual speakers have varying
impedances, which may require revised filter calculations
and optimization. Furthermore, your application may have
different design goals than those chosen for the LX1710
evaluation board.
LXE 1710 EVALUATION BOARD U
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Rev. 1.1, 2000-12-01
MOSFET SELECTION
As seen in previous sections, the user can design the
output filter of the amplifier to meet performance or
costs targets. In addition, the amplifier’s power stage
(selection of MOSFET s ) c an be s elect ed depending on
these tradeoffs. The efficiency of the amplifier circuit
can be approximated by the following equation.
CROSSLINDPDSNDS
L
IN
OUT
PRRRRI RI
P
P++++
== ])(2[
2
2
Where
RL = DC Resistance of Speaker
RNDS = n-channel MOSFET on-resistance
RPDS = p-channel MOSFET on-resistance
RIND = DC Resistance of Inductor
PCROSS = MOSFET Switching Loss
The overall efficiency is a function of primarily the
MOSFETs and output filter inductors. The “Inductor”
section’s contribution will be considered later. The
MOSFET Power los s is a function of the on-resistance
and gate charge.
A
R
P
I
WP
RRIP
O
PDSNDSDS
5.2
4
25
Then
4at 25If
)](2[LossPower MOSFET 2
===
Ω= +==
The LX1710 Evaluation Board is designed using
FDS4953 p-channel and FDS6612A n-channel
MOSFETS.
WP
RR
DS
PDSNDS
56.1)]095.003.0(2[)5.2(
095.0 ,03.0
2=+= Ω=Ω=
MOSFET power loss is proportional to on-resistance.
nfCVPS
CROSS 2
Loss Switching MOSFET ==
Where
C = Input Capacitance
V = Supply Voltage
fS = Switching Frequency
n = Number of MOSFETS
Assume C = 1000pF
V = 15VDC
fS = 500kHz
WPCROSS 45.0)4)(10500)(15)(101( 329 =××= −
MOSFET switching loss is proportional to total gate
charge, supply voltage, and switching frequency.
There are a few other important parameters to
consider when selecting the output power components
besides the on-resistance and gate charge of the
MOSFETs. The drain-source voltage must provide
ample margin for circuit noise and high speed
switching transients. Since the amplifier configuration
requires output bridge operation at the supply voltage,
the MOSFETs should have a drain-source voltage of
at least 50% greater than the supply voltage. The
power dissipation of the MOSFETs should also be
able to dissipate the heat generated by the internal
losses and be greater than the sum of P DS and PCROSS.
Linfinity recommends that in selecting MOSFETs, RDS
0 1!1 2
g <10nC. The table below provides
several MOSFET options.
FDS6612A FDS4953 Si4532ADY IRF7105
n-channel p-channel n-channel p-channel n-channel p-channel
Drain-Source On-Resistance RDS(ON)@VGS = +/-10V
0.022 0.053 0.053 0.08 0.10 0.25
Drain-Source Voltage VDSS (V) 30 -30 30 -30 25 -25
Drain Current (continuous) ID(continuous) (A) 8.4 -5 4.9 -3.9 3.5 -2.3
Total Gate Charge Qg (typi c al ) (nC) 9 8 8 10 9.4 10
Manufacturer Fairchild Fairchild
Vishay
Siliconix
Vishay
Siliconix
International
Rectifier
International
Rectifier
MOSFET Component Opti ons
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Rev. 1.1, 2000-12-01
INDUCTOR SELECTION
The output filter inductors are key elements in the
performance of the Class-D audio power amplifier.
Inductor selection criteria also involves tradeoffs
between performance (efficiency) and component
costs. The critical specifications for the inductor are
the DC resistance, DC current, and peak current
ratings. The inductors should be able to handle the
amplifier’s power as well as operate within its linear
region. Saturating the inductors could decrease
performance (increase THD) and even produce a
short, which may damage either the circuit or the
speaker.
Other variables when selecting an inductor depend on
the switching frequency of the designed amplifier. A
higher switching frequency implies that the corner
frequency of the LC filter is higher. With a higher fC,
the inductor value is smaller.
The amplifier’s application and design constraints will
help determine whether the inductors are selected for
size, power, or performance. Various inductors such
as those that are s hielded may also have diff erent EMI
effects and distortion performance.
The overall ef f iciency (
) of the amplif ier cir c uit is given
in the previous MOSFET section. The inductor’s
power loss contribution is a function of the inductor’s
DC resistance, RIND.
))(2)(( LossPower Inductor 2INDIND RIP ==
The LX1710 Evaluation board utilizes two 15µH radial
leaded R.F. inductors from Inductor Supply, Inc. (ISI).
When evaluating component options, inductors such
as from Coilcraft can be used for other performance /
price tradeoffs. See inductor table below.
WPIND 7.0)056)(.2)(5.2( 2==
The efficiency approximation can now be completed.
%2.90
2545.7.56.1 25
])(2[
2
2
2
2
=
+++
=
+++
=
++++
==
LCROSSINDDS
L
CROSSLINDPDSNDS
L
IN
OUT
RIPPP
RI
PRRRRI
RI
P
P
The efficiency is a function of the power and switching
loss in the MOSFETs and inductors.
Manufacturer Part Number Inductance
Q min Test
Frequency DC Resistance
DC Current
max (ARMS)
Self Resonant
Frequency min
(MHz)
ISI RL622-150K 15.0 50 2.520MHz 56 2.50 12.0
Coilcraft
DO5022P-153HC 15.0 100kHz 32 4.4 20
Inductor Component Opt i ons
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Rev. 1.1, 2000-12-01
CAPACITOR SELECTION
The LC filter design section discusses filter options
and the calculation of component values. However,
the specification of capacitor type depends on the
application in the circuit. The table provides
descriptions and guidelines for capacitors in the
AudioMAX amplifier board.
Reference
Designator Capacitor Comments
C10, C11 FET gate drive These
! "#! $! $ "! % #! &'!
C3 C14 Audio input path Thes e decoupling capac i tors are used f or t he audi o i nput +/- signal s.
C18, C19,
C20, C21 Output fi l ter The output filter metal film capacitors (low ESR, 5% tolerance) work well to set an accurate
corner frequenc y at a low cost .
C8, C12 FET bypass These metal film capacitors are used for the power supply bypass for the FETs. Place
adjacent to the FETs or consider lower value ESR solutions depending on the PCB
com ponent pl acement .
C22 LX1710 bypass The metal f i l m capac i tor is a high f requency bypass f or t he LX1710 IC.
C9, C13 VDD,
PVDD bypas s These tantalum capacitors provide the bypass for the IC supply voltage and output driver
supply voltage utilizing a minimal footprint area.
C17 Output power stage The electrolyti c filt er capaci tor sm oothes out ripple current and should be plac ed close t o the
output FETs .
C16 Oscillator frequency The timing c apacitor (5% tolerance) sets t he oscillator frequency.
C6, C7 Feedback f i l t er These (5%) c apacitors are used in the RC fi l ter to provide feedback for t he c ontrol loop.
C4, C5 Error ampl i fier These (5%) capacitors create the compensation network. Make sure the appropriate
“temperature grade” is used to ensure stability.
C1, C2 Voltage ref erences The filt er c apacitors provi de the bypass f or the 5V and 2.5V references.
C26 Audio input filter The RC filt er minimizes high frequency noise to the am pl i f i er.
Capacitor Descripti on
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GATE RESISTOR
Series resistors (R6, R10, R11, R12) can be added to
the gate of MOSFETs (Q1 to Q4) to control the
switching transition times. This reduces signal
distortion as seen in the THD+N vs. Output Power
graph below. The slower switching speeds will
however, increase power dissipation and therefore
slightly decrease the overall efficiency of the amplifier.
P+
N+
OUT+
VIN
Q1
Q2
R12
10 Ω
R11
10 Ω
- 3451 . 1 $
resistors, which improves (decreases) the THD+N
from 0.1% to 0.05% with a slight impact on efficiency
of appr oxim ately 2%. T he recom m ended gate resistor
1 6!
OSCILLATOR CONFIGURATION
The oscillator is programmed by the external timing
components RPWM and CPWM. For a nominal
frequency of 333kHz, RPWM and CPWM should be
set to 49.9kOhms and 100pF respectively. Note that
in order to keep the slope of the PWM ramp voltage
proportional to the supply voltage, both the ramp peak
and valley voltages, and the charge and discharge
currents are proportional to the supply voltage. This
keeps the frequency relatively constant while keeping
the slope of the PWM ram p proportional to the voltage
on the VDD pin. For operating frequencies other than
333kHz, the frequency can be approximated by the
following equation:
nsCR PWMPWM 320))()(577.0( 1
Frequency +
=
MULTI CHANNEL REQUIREMENTS AND FREQUENCY
SYNCHRONIZATION
For applications that require more than a single
channel, the oscillators of multiple LX1710/1711
controllers can be configured for synchronous
operation. One unit, the master, is programmed for
the desired frequency with the RPWM and CPWM as
usual. Additional units will be slave units, and their
oscillators will be disabled by leaving the RPWM pin
disconnected. The CLOCK pin and the CPWM pin of
the slave units should be tied to the CLOCK pin and
the CPW M pin of the master unit respectively. In this
configur ation, the CLOCK pins of the slave units begin
receiving instead of transmitting clock pulses. Also,
the CPWM pins quit driving the PWM capacitor in the
slave units. Note that for optimum performance, all
slave units should be located within a f ew inches of the
master unit.
Gate Resistor Impact On THD+N
0.001
100
0.005
0.01
0.1
1
2
10
20
50
0.26978
0.04675
THD+N (%)
50m 30
100m 200m 500m 1 2 5 10 20 24.56
1.131
O utput P ower (W)
N o Ga te R e s is to r
With 1 0 Ω G ate Resistor
VIN = 15V fIN = 1kHz RL
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Page 15
Copyright 2000
Rev. 1.1, 2000-12-01
PCB LAYOUT RECOMMENDATIONS
Like most analog circuits, component placement,
signal routing, and power/ground isolation can affect
the overall performance of the design. The layout
should utilize individual ground traces/planes for the
audio amplifier whenever possible. The audio input
and controller ground, FET ground, and output filter
ground are routed using a “star” connection in the
LXE1710 evaluation board. See PCB layer views.
The power to the controller IC should be routed using
separate traces that do not carry high current pulses
from the switching circuit. In general, minimizing the
high frequency, high power currents from flowing
through the same copper as the audio signal
references are recommended. Signal traces that
could be sensitive to noise should be node to node
connections ( no “ shar ed” traces ). Str ay capacitance at
the controller pins RPW M, EAOUT , EAIN, and FAOUT
can affect the circuit performance and components
associated with these pins should be placed as close
to the controller IC as possible.
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Rev. 1.1, 2000-12-01
PRINTED CIRCUIT BOA RD LAYOUT
Silkscreen Layer
CN1: RCA Jack
Audio In J3: Optio nal Connections
Audio In +, Audio In - TB1: Power Supply Terminal Block
+V, GND
J2: Mute Jum
p
er
J1: Sleep Jumper TB2: Audio Outp ut Terminal Block
+ OUT, - OUT
LXE 1710 EVALUATION BOARD U
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Copyright 2000
Rev. 1.1, 2000-12-01
PRINTED CIRCUIT BOARD
Bottom Layer
Top Layer
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Page 18
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Rev. 1.1, 2000-12-01
BILL OF MATERIALS
Line
Item Part Description Manufacturer & Part # Case Reference
Designators Qty
1 Controller
LX1710 SSOP 28 U1 1
2 N-Channel MOSFET
FDS6612A SO-8 Q2, Q4 2
3 P-Channel MOSFET
FDS4953 SO-8 Q1, Q3 2
4 Printed Circui t Board
SGE2758 REV.X 1
5 Inductor, 15uH
RL622-150K TH L1, L2 2
6 Phono Jacks, 90° Nickel Plated, Wht
161-4214 TH CN1 1
7 Strip Line Pl ugs, Strai ght, Singl e Row .100"
CA-S36-24B-44 TH J1, J2 2
8 Shorting Jumpers, Open Top, Black
151-8030 TH J1 1
9 Terminal Bl ock 2 pos 5mm
301-021-1000 TH TB1, TB2 2
Line
Item Part Description Part Description Case Reference
Designators Qty
1 Capacitor, COG, 18pF, 50V, 5%
1206N180J500NT
12065C180JAT2A 1206 C5 1
2 Capacitor, COG, 150pF, 50V, 5%
1206N151J500NT
12065C151JAT2A 1206 C4 1
3 Capacitor, COG, 220pF, 50V, 5%
12065C221JAT2A 1206 C6, C7 2
4 Capacitor, X7R, 330pF, 50V, 10%
ECU-V1H331KBM 1206 C26 1
5 Capacitor, X7R, .47uF, 16V , 20%
1206B474M160NT
1206YC474MAT2A 1206 C3, C14 2
6 Capacitor, X7R, 1uF, 50V, 10%
1206B105K500NT
12065C105KAT2A 1206 C1, C2 2
7 Capacitor, COG, 100pF, 50V, 5%
0805N101J500NT
08055C101JAT2A 0805 C16 1
8 Capacitor Tant 0. 1uF 35V 20%
TAJA104M035R 3216 C9 1
9 Capacitor Tant 2. 2uF 25V 20%
!
T491A225M025AS 3216 C13 1
10 Capacitor, Tant , 4.7uF, 16V, 20%
!
T491A475M016AS
TAJA475M016R 3216 C10, C11 2
11 Capacitor Stacked MF 0.1uF 50V 5%
ECQ-V1H104JL TH C8, C12, C22 3
12 Capacitor Stacked MF 0.47uF 50V 5%
ECQ-V1H474JL TH C18, C19 2
13 Capacitor Stacked MF 0.68uF 50V 5%
ECQ-V1H684JL TH C20, C21 2
14 Capacitor, Elect 220uF, 25V, 20%
"
RV-25V221MH10-R NT C17 1
Line
Item
Part Description Part Description Case Reference
Designators Qty
1 Resistor, 10K, 5%, 1/4W
#
CR32J103T 1206 R2 1
2 Resistor, 24. 3K, 1%, 1/ 4W
#
CR32F2432T 1206 R3, R4 2
3 Resistor, 10 Ohm, 5% , 1/8W
#
CR J100T 0805 R6, R10, R11, R12 4
4 Resistor, 10K, 5%, 1/8W
#
CR21J103T 0805 R8, R9 2
5 Resistor, 34.8K, 1%, 1/8W
#
CR21F3482T 0805 R5 1
6 Resistor, 20K, 5%, 1/8W
#
CR J203T 0805 R7 1
7 Resistor, 56.2K, 1%, 1/8W
#
CR21F5622T 0805 R1 1
8 Resistor, 15 Ohm 5% 1W
$
RM73B3A150J
%!
MCR100JZHJ150 2512 R13 1
9 Resistor, Low Value Fl at .0374
%
LR2010-01-R0374-F 2512 RS1 1
