LM49250 Evaluation Board
User Guide
National Semiconductor
Application Note 1680
Nisha Patel
March 9, 2010
Introduction
The LM49250 is a fully integrated audio subsystem designed
for stereo cell phone applications. The LM49250 combines
2.5W stereo Class D speaker drivers with stereo ground ref-
erenced headphone drivers, a class AB earpiece driver, Na-
tional 3D enhancement, volume control and input mixer into
a single device. The filterless class D amplifiers deliver
1.19W/channel into an 8
Ω
load with <1% THD+N from a 5V
supply.
The LM49250 features a new circuit technology that utilizes
a charge pump to generate a negative supply voltage. This
allows the outputs to be biased about ground, thereby elimi-
nating output-coupling capacitors typically used with normal
single-ended loads. To supply the required voltage level to
the ground referenced amplifier, an LDO has been integrated.
For improved noise immunity, the LM49250 features fully dif-
ferential left, right and mono inputs. The three inputs can be
mixed/multiplexed to either the loudspeaker, headphone or
earpiece amplifiers. The left and right differential inputs can
be used as separate single-ended inputs, mixing multiple
stereo audio sources. The mixer, volume control, and device
mode select are controlled through an I2C compatible inter-
face.
Output short circuit and thermal overload protection prevent
the device from being damaged during fault conditions. Su-
perior click and pop suppression eliminates audible transients
on power-up/down and during shutdown.
The LM49250 Evaluation board (shown in Figure 1) allows
the user to easily evaluate the performance and characteris-
tics of the LM49250 device. It provides connectors for audio
inputs, audio outputs, I
2
C control, power supply, and shut-
down control.
Quick Start
1. Connect a shunt across the center pin (I
2
C VDD) and VDD
pin of J9 (I
2
CVDD = VDD).
2. Connect a shunt across the center RESET pin and the “+”
terminal of J4 (I2C reset pin).
3. Connect a 4
Ω
or 8
Ω
speaker across the “+” and “-” pins of
J2 (left loudspeaker output) and J3 (right loudspeaker
output).
4. Connect stereo headphones to the headphone jack (U2).
5. Connect a 16
Ω
or 32
Ω
speaker across the “+” and “-” pins
of J1 (earpiece output).
6. Connect a 3.6V power supply to the VDD pin of J8, and the
power supply ground source to the GND pin of J8.
7. Apply a positive audio signal source to the “+” terminals of
J5 (right input), J6 (left input), and J7 (mono input), and a
negative audio signal source to the “-” terminals of J5 (right
input), J6 (left input), and J7 (mono input).
8. Connect the USB interface card to a PC with the USB cable.
Connect cable attached to USB interface card to the
I
2
C interface jumper (J10)on demo board.
9. Open LM49250 I
2
C interface software.
10. Turn on power supply and audio source.
11. In the LM49250 I
2
C interface software (see Figure 2)
select:
a. “ON” for Earpiece, Left Loudspeaker, Right Loudspeaker,
Left Headphone, and Right Headphone
b. Mode “2” for Loudspeaker Output Mode, Headphone
Output Mode, and Earpiece Output Mode
12. Select Chip Power to “ON” to enable the device.
13. Adjust the Left, Right, and Mono Volume Control to obtain
the desired output level.
Operating Conditions
• Temperature Range
–40°C
≤
T
A
≤
+85°C
• Supply Voltage
(V
DD
= V
DD(LS)
= V
DD(CP)
)
2.7V
≤
V
DD
≤
5.5V
• I
2
C Supply Voltage
1.7V
≤
I
2
CV
DD
≤
5.5V
I
2
CV
DD
≤
V
DD
© 2010 National Semiconductor Corporation
300291
www.national.com
LM49250 Evaluation Board User Guide
AN-1680
