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Obsolete
LX1792 Eval CLASS-D AUDIO
AMPLIFIER
EVALUATION BOARD
USER GUIDE
Copyright © 2002
Rev 0.3, 3/4/2002
INTEGRATED PRODUCTS
Power Management
Page 2
Obsolete
LX1792 E
LX1792 Evaluation Board Features and Circuit Description .........................................................2
Input Select
Gain Set
Impedance Select
Output Select
Filter Stage
Breadboard
Quick Start Guide ............................................................................................................................4
Evaluation Board Schematic ...........................................................................................................6
Bill of Materials ................................................................................................................................7
VALUATION BOARD USER GUIDE
TABLE OF CONTENTS
Copyright © 2002 Microsemi Page 2
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
Obsolete
LX1792 E
VALUATION BOARD USER GUIDE
FEATURES AND CIRCUIT DESCRIPTION
• Fully Assembled Mono Evaluation Board
with LX1792 Class-D Audio Amplifier
• Supports hearing aid bandwidth (100Hz -
10kHz)
• Gain set by 2 external resistors
• Three output impedance settings (10Ω,
15Ω, 34Ω)
• Optimized to drive 200Ω speaker load
The LX1792 Evaluation Board allows the user to
quickly connect and evaluate the LX1792
Switching Class-D Mono IC. Banana jacks are
provided for power supply connections. A RCA
jack is supplied to input an audio signal, and a BNC
connector is provided for a signal generator input.
A slide switch is provided for easy selection
between the two inputs. A ¼" audio jack is
provided to connect headphones to the amplifier
output. A single-ended, low-pass filtered output is
also available through a BNC connector. This
allows the user to connect the LX1792 output to
either a spectrum analyzer or an oscilloscope.
Breadboard space is also provided on the evaluation
board to offer the user the opportunity to attach a
different filter and/or load.
• Banana jacks for power supply connections
• RCA jack for audio input
• BNC jack for signal generator input
• ¼" Audio jack for headphone connection
• Single-ended output for measurement and
analysis
The Class-D amplifier generates a Pulse Width
Modulated output by controlling FETs that are
connected in a H-Bridge configuration. The full
bridge configuration is connected between the
single supply voltage (VDD) and ground (VSS),
with the output of the bridge driving a speaker or an
equivalent load.
Because the FETs have an extremely low "on"
resistance and an extremely high "off" resistance,
the majority (95% typical) of the power is delivered
to the load, making it a highly efficient amplifier.
The only external component required by the
LX1792 is an input AC coupling capacitor. The
evaluation board contains two power supply filter
capacitors, however, these are not mandatory for
operation. The output of the LX1792 can be directly
connected to a speaker.
I
NPUT SELECT
The Evaluation Board provides two input
connection options: a BNC connector and a RCA
connector. The BNC connector should be used
when inputting a signal from a function generator.
The RCA connector should be used when inputting
a signal from an audio source. A slide switch is
provided to choose between these two input
connectors.
G
AIN SET
Gain in the LX1792 amplifier can be set to a
maximum total gain of 40dB. The preamp gain is
set by the ratio of the external resistors (R2/R1).
There is an additional 10dB gain in the H-bridge.
I
MPEDANCE SELECT
Three different output impedances are available
with the LX1792. A slide switch allows users to
choose between an output impedance of 10W, 15W,
and 34W. The higher output impedance settings
reduce current consumption of the LX1792.
O
UTPUT SELECT
The LX1792 evaluation board provides a slide
switch that allows the user to choose between three
different output options. When the switch is in the
"Headphone" position, the differential output of the
amplifier is applied directly to the headphone jack.
If the "Single-Ended" option is chosen, the
differential output is converted to a single ended
output with a transformer, and then low-pass
filtered. The "Unloaded" option removes the load
from the amplifier output. This option can be used
Copyright © 2002 Microsemi Page 3
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
Obsolete
LX1792 E
VALUATION BOARD USER GUIDE
if the user wants to connect the amplifier to a
custom load on the breadboard.
F
ILTER STAGE
If the single-ended output is chosen, the amplifier
output is connected to a transformer and then to a
first order RC low-pass filter, with a cutoff
frequency of 20kHz. This filter removes the
200kHz switching frequency from the signal.
B
READBOARD
The LX1792 gives the user the option of connecting
the amplifier to a custom filter and load. The
differential output of the LX1792 is wired directly
to the breadboard. These signals are labeled
"OUTP" and "OUTN" for the positive and negative
outputs, respectively. The breadboard is also wired
with ground for convenience. A BNC connector is
provided to access the breadboard output.
Copyright © 2002 Microsemi Page 4
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
Obsolete
LX1792 E
VALUATION BOARD USER GUIDE
QUICK START GUIDE
The LX1792 Evaluation Board is a fully
functional, Class-D Amplifier. To begin evaluation
of the LX1792, just follow these simple steps.
1) Visually inspect the board to make sure
that components were not damaged during
shipping.
transformer and convert it to a singleended signal. The single-ended signal is
then low-pass filtered with a cutoff
frequency of 20kHz. The output of the
low-pass filter is connected to BNC jack
J5. The "Unloaded" setting will
disconnect the amplifier fro m either load.
2) Power and Ground Connections
power and ground connections are made
through banana jacks J3 and J4. Connect
the positive terminal of the power supply
or battery to J3, which is labeled "VDD".
Connect the negative terminal of the
supply or battery to J4, which is labeled
"VSS". Make sure the correct connections
are made before turning on power supply.
3) Input Connection
To input a function generator signal,
connect source to jack J1, labeled "BNC
IN". To input an audio signal, connect
source to jack J2, labeled "RCA IN".
4) Input Selection
If using the BNC jack, set Input Select
switch SW1 to the "BNC" position. If
using the RCA jack, set SW1 to the
"RCA" position.
5) Gain Set
Choose the gain by selecting the external
resistors (R1>25Kohms). Gain = 10dB +
20log(R2/R1)
6) Output Impedance Selection
For most Evaluation Board applications,
the Impedance Select switch SW2 should
be set to 10Ω. The other impedance
settings reduce current consumption with
the tradeoff of increasing switch output
impedance.
The
8) Output Connection
To listen to the output of the amplifier,
connect headphones to J7, labeled
"Headphone OUT", and verify that the
Output Select is set to "Headphone".
Headphones with a minimum impedance
of 150Ω should be used. To view the
amplifier output on either a spectrum
analyzer or an oscilloscope, connect to
BNC connector J5, labeled "Single-Ended
OUT", and verify SW4 is set to "SingleEnded".
9) Breadboard
The differential output signal is directly
available on the breadboard. The positive
output is labeled "OUTP", and the
negative output is labeled "OUTN". The
power supply ground is also available on
the breadboard, and is labeled "GND".
BNC connector J6 is provided to access
the breadboard output, which is labeled
"BREADBOARD OUT". The positive
output pin of J6 is wired to the breadboard,
and is labeled "BB OUT". When using the
breadboard, make sure the Output Select
switch is set to "Unloaded".
10) Power Source
If using a power supply, verify that it is set
to 1.25V before connecting it to the
Evaluation Board. A "C" (1.5V) battery
can also be used.
7) Output Select
The "Headphone" setting will directly
connect the differential output of the
amplifier to the headphone jack. The
"Single-Ended" setting will connect the
differential amplifier output to a
Copyright © 2002 Microsemi Page 5
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
11) Signal Generator Source
Set the signal generator to the appropriate
level for best results (see examples in table
below).
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LX1792 E
VALUATION BOARD USER GUIDE
Vin Gain Setting
50mVrms 20dB
25mVrms 26dB
13mVrms 32dB
6mVrms 38dB
12) Audio Source
Verify that a low level audio source is
being used, and set it to the minimum
level. Start or "play" audio source and
adjust volume to desired level.
13) Listen
If the LX1792 is not operating properly,
verify the preceding steps or contact
Microsemi MicroPower for technical
assistance (760) 431-5490.
Copyright © 2002 Microsemi Page 6
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
Obsolete
LX1792 E
VALUATION BOARD USER GUIDE
EVAL SCHEMATIC
Out M
Out P
Breadboard
BNC
1
2
Impedence Select
5678
1234
15Ω
30Ω
BNC
IN
2
RCA
IN
2
1
BNC
1
RCA
SW2
10Ω
12
6
Output
Single Ended
Headphone
Unloaded
LX1790
U1
1
2
3
4
5
6
7
Input
Select
R1 R2
C5
3
45
Selector
4
3
2
1
14
13
12
11
10
9
8
5
6
7
8
Figure 1 – Evaluation Board Schematic
Single Ended
1
2
3
J3
Banana
J4
Banana
OUT BNC
C6
Headphone
OUT
2
1
2
34
C1
C2
R3
61
5
Copyright © 2002 Microsemi Page 7
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
Obsolete
LX1792 E
VALUATION BOARD USER GUIDE
BILL OF MATERIALS
MISCELLANEOUS COMPON
Line
Item
1 Class-D Amplifier IC
2 Banana Jack, Black
3 Banana Jack, Red
4 BNC Connector
5 DPDT Slide Switch
6 DP3T Slide Switch
7 RCA Jack, Red
8 Transformer
9 14 Pin Cerdip Socket
10 ¼” Stereo Jack
Line
Item
1 Capacitor, 5mF, Electrolytic C1 1
2 Capacitor, 1nF C6 1
3 Capacitor, 100nF Ceramic C2, C5
Line
Item
1
2 Resistor, >25kW R1 1
3 Resistor (Sets gain) R2 1
* Evaluation Board contains 1 LX1792CN part, order additional samples separately.
Part Description Manufacturer & Part # Case
Part Description Part Description Case
Part Description Part Description Case
Resistor, 5.1kΩ
MISCELLANEOUS COMPONENTS
MISCELLANEOUS COMPONMISCELLANEOUS COMPON
M
ICROSEMI LX1792CN *
M
OUSER 164-6218
M
OUSER 164-6219
M
OUSER 523-31-5486-1010
M
OUSER 612-EG2201
M
OUSER 612-EG2301
M
OUSER 161-0096
M
OUSER 42TL016
M
OUSER 571-26403574
M
OUSER 161-0030
CAPACITORS
CAPACITORS
CAPACITORSCAPACITORS
RESISTORS
RESISTORS
RESISTORSRESISTORS
R3 1
ENTS
ENTSENTS
Reference
Designators
U1 1
TH J4 1
TH J3 1
J1, J5, J6 3
SW1 1
SW2, SW3, SW4 3
J2 1
T1 1
U1 1
J7 1
Reference
Designators
Reference
Designators
Qty
Qty
Qty
Copyright © 2002 Microsemi Page 8
Rev 0.2, 3/4/2002 Integrated Products – Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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