LX1790 E
VALUATION
B
OARD
U
SER
G
UIDE
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
F
EATURES AND
C
IRCUIT
D
ESCRIPTION
•
Fully Assembled Mono Evaluation Board
with LX1790 Class-D Audio Amplifier
•
Supports hearing aid bandwidth (100Hz -
10kHz)
•
Three gain settings (14dB, 20dB, 26dB)
•
Three output impedance settings (10
Ω
,
15
Ω
, 34
Ω
)
•
Optimized to drive 200
Ω
speaker load
The LX1790 Evaluation Board allows the user to
quickly connect and evaluate the LX1790
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 LX1790 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.
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.
•
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
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
LX1790 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 LX1790 can be
directly connected to a speaker.
I
NPUT
S
ELECT
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
S
ELECT
Three different gain settings are available with the
LX1790 amplifier. A slide switch is provided on
the evaluation board to allow the user to choose
between gain settings of 14dB, 20dB, and 26dB.
I
MPEDANCE
S
ELECT
Three different output impedances are available
with the LX1790. A slide switch allows users to
choose between an output
impedance of 10
Ω
, 15
Ω
,
and 34
Ω
. The higher output impedance settings
reduce current consumption of the LX1790.
O
UTPUT
S
ELECT
The LX1790 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
if the user wants to connect the amplifier to a
custom load on the breadboard.
