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Texas Instruments AN-1680 LM49250 Evaluation Board (Rev. A) User guides
User's Guide
SNAA048A – March 2010 – Revised May 2013
AN-1680 LM49250 Evaluation Board
1
Introduction
The LM49250 evaluation board 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 referenced
headphone drivers, a class AB earpiece driver, TI 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 5 V 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 eliminating 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 differential 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 interface.
Output short circuit and thermal overload protection prevent the device from being damaged during fault
conditions. Superior 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 characteristics of the LM49250 device. It provides connectors for audio inputs, audio outputs, I2C
control, power supply, and shutdown control.
2
Quick Start
The following procedures are needed to begin the
1. Connect a shunt across the center pin (I2C VDD) and the VDD pin of J9 (I2CVDD = VDD).
2. Connect a shunt across the center RESET pin and the “+” terminal of J4 (I2C reset pin).
3. Connect a 4Ω or 8Ω 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 16Ω or 32Ω 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 I2C interface jumper (J10)on demo board.
9. Open LM49250 I2C interface software.
10. Turn on the power supply and audio source.
11. In the LM49250 I2C interface software (see Figure 2) select:
• “ON” for Earpiece, Left Loudspeaker, Right Loudspeaker, Left Headphone, and Right Headphone
• Mode “2” for Loudspeaker Output Mode, Headphone Output Mode, and Earpiece Output Mode
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1
Quick Start
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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.
Table 1. Operating Conditions
• Temperature Range
–40°C ≤ TA ≤ +85°C
• Supply Voltage
(VDD = VDD(LS) = VDD(CP))
2.7V ≤ VDD ≤ 5.5V
• I2C Supply Voltage
1.7V ≤ I2CVDD ≤ 5.5V
I2CVDD ≤ VDD
VDD
VDD
C12
C11
R1
0:
R2
0:
VDD GND
C13
C14
C15
4.7 PF
4.7 PF
4.7 PF
J8
C1
VDD(CP)
1 PF
+
IN_M
_
VDD GND GND
VDD(LS)
L3D1 L3D2 R3D1 R3D2
MIN+
EP+
MIN-
EP-
J7
J1
+
_EP
C2
J2
1 PF
C3
1 PF
+
IN_L
_
LLS+
+
LLS-
LS_L
_
J3
L1/LIN+
J6
L2/LINC4
RLS+
+
RLS-
_
LS_R
J11
1 PF
HP_R
GND
C5
1 PF
+
IN_R
_
HPR
R1/RIN+
J5
HPL
GND (HP)
R2/RIN-
J12
C6
1 PF
BYPASS
C7
4.7 PF
HP_L
VO (LDO)
GND (CP)
GND(LS)
2
I CVDD
SDA ADR SCL
C16
RESET
VSS(CP)
CCP+
U2
GND
C10
2.2 PF
CCP-
VDD
1 PF
C8
SCL I2CVDD
ADR
GND
SDA
J9
+
2.2 PF
t
J4
C9
2.2 PF
J10
Figure 1. Evaluation Board Schematic
Table 2. Board Connectors
2
Designator
Label
J1
EP
Function
Mono BTL earpiece audio output
J2
LS_L
Left loudspeaker class D audio output
J3
LS_R
Right loudspeaker class D audio output
J4
RESET
J5
IN_R
I2C Reset Pin - For normal operation short the center RESET pin to the “+” pin.
To reset the PWR_ON bit in the shutdown control register short the center
RESET pin to the “-” terminal.
Right, single ended or differential, audio input terminal
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I2C Software Interface
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Table 2. Board Connectors (continued)
Designator
Label
J6
IN_L
Left, single ended or differential, audio input terminal
J7
IN_M
Mono differential audio input terminal
J8
VDD GND
I2CVDD
J9
Function
Power Supply Connection
If a separate I2C power supply voltage is used: Connect the positive voltage
source to the center I2CVDD terminal and the ground source to the pin on J9
labeled GND. If a separate I2C power supply is not used: Connect the center
I2CVDD to the pin on J9 labeled VDD.
I2C signal terminals. Pin 1 is for the SCL signal, pin 2 is for the ADR signal, pin
3 is for the SDA signal, pin 4 is for I2C VDD, and pin 5 is ground (as labeled on
the evaluation board).
J10
J11
HP_R
Right ground referenced headphone output terminal
J12
HP_L
Left ground referenced headphone output terminal
Table 3. Evaluation Board Bill of Materials
3
Designator
Part Description
Manufacturer
Part Number
C1 – C6
Ceramic capacitor 1μF 16V X7R 1206 10%
muRata
GRM319R71C105KC11D
C7, C13, C14, C15
Ceramic capacitor 2.2μF 16V X5R 0805
muRata
GRM21BR61C225KA88L
C8, C9, C10
Ceramic capacitor 2.2μF 16V X5R 0805
muRata
GRM21BR61C225KA88L
C11, C12
Ceramic capacitor 68nF 16V X7R 0805
muRata
GRM188R71C683KA01D
C16
Ceramic capacitor 1μF 16V X7R 0805
muRata
GRM21BR71C105KA01L
R1, R2
Resistor 0W 1/8W 5% 0805 SMD
I2C Software Interface
The LM49250 evaluation board is controlled through an I2C compatible USB interface. The LM49250 I2C
interface software provides a user friendly interface to easily evaluate the functionality of the device. Each
button corresponds to bits in an I2C command byte. For detailed I2C information, see the LM49250 data
sheet.
Figure 2. LM49250 I2C Software Interface
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Default
4
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Default
The DEFAULT button sets the LM49250 and the interface software to its default state. In the default state
all output amplifiers, spread spectrum, and 3D controls are off, all output modes are set to 0, the fully
differential input mode is selected, all input gains are set to -64dB, right and left loudspeaker output gain is
6dB, and headphone and earpiece output gain are set to 0dB. Each time the power supply to the device is
cycled, the interface must be reset to its default state.
5
Chip Power
The Chip Power button enables or disables the entire device. Even if an individual amplifier channel is
enabled, the device will not output any audio if the Chip Power button is set to “OFF”.
6
LDOH
The LDOH button enables and disables the internal LDO. The LDO is used to drive the ground referenced
headphone amplifiers. This allows the speaker and headphone amplifiers to operate from separate power
supplies. The separate power supplies allow the speaker amplifiers to operate from a higher voltage for
maximum headroom, while the headphone amplifiers operate from a lower voltage, improving power
dissipation.
If the LDO and the Chip Power is enabled, 2.25V will be seen at the VO(LDO) pin. However, if the LDO is
disabled but either headphone output is enabled, 2.25V will be seen at the VO(LDO) pin (see Table 3).
Table 4. LDO Disabling Options
7
LDOH
HPR_ON/HPL_ON
PWR_ON
VO(LDO) (V)
0
0
X
0
0
1
1
2.25
1
X
0
VDD
1
1
0
2.25
0
1
0
Spread Spectrum
The LM49250 features a filterless spread spectrum modulation scheme. The switching frequency varies
which reduces the wideband spectral content. This improves EMI emissions radiated by the speaker and
associated cables and traces. The spread spectrum function can be turned on and off through the “SS”
section of the interface software.
8
Input Audio Signal Selection
The LM49250 has a single mono differential input and left and right stereo inputs that can be configured
for both single-ended and differential audio signals. The stereo input configurations can be set in the
“STEREO INPUT CONFIGURATION” portion of the software interface.
• Select “FULLY DIFFERENTIAL INPUT MODE” to configure the left and right inputs for differential
operation.
• Select “L2 and R2 SINGLE-ENDED STEREO PAIR” to configure the device to accept single ended
audio inputs connected to L2 and R2.
• Select “L1 and R1 SINGLE-ENDED STEREO PAIR” to configure the device to accept single ended
audio inputs connected to L1 and R2.
• Select “(L1 mix L2) and (R1 mix R2) SINGLE ENDED STEREO PAIR” to configure the device to
accept two single ended stereo sources, connected to both input pairs.
4
AN-1680 LM49250 Evaluation Board
SNAA048A – March 2010 – Revised May 2013
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Volume Control and Gain Setting
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9
Volume Control and Gain Setting
Each channel of the LM49250 has two separate gain stages. Each input stage (mono, left and right)
features a 32 step volume control that can be configured through the “INPUT VOLUME CONTROL”
section of the interface software. The output gain settings can be set under the “Output Gain Settings” tab
in the interface software. The loudspeaker output gain for the left and right channels are set
independently, while the headphone gain is the same for both left and right channels.
The earpiece output stage has two gain settings, 0dB and 6dB. Each loud speaker output stage has two
gain settings, 6dB and 12dB. The headphone output stage has 8 gain settings, 0dB, -1.2dB, -2.5dB, -4dB,
-6dB, -8.5dB, -12dB and -18dB. In single-ended input mode with only one stereo signal applied, the
loudspeaker and headphone output stage gain settings are increased by 6dB. The total gain for a given
signal path can be calculated by adding the input volume control gain to the output gain setting.
10
Demonstration Board Layout
Figure 3. Top Silkscreen
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Demonstration Board Layout
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Figure 4. Top Layer
Figure 5. Layer 2
6
AN-1680 LM49250 Evaluation Board
SNAA048A – March 2010 – Revised May 2013
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Copyright © 2010–2013, Texas Instruments Incorporated
Revision History
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Figure 6. Layer 3
Figure 7. Bottom Layer
11
Revision History
Rev
Date
Description
1.0
03/09/10
Initial WEB released.
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Revision History
8
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AN-1680 LM49250 Evaluation Board
SNAA048A – March 2010 – Revised May 2013
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Copyright © 2010–2013, Texas Instruments Incorporated
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