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Texas Instruments AN-1622 LM49100 Evaluation Board (Rev. A) User guides
User's Guide
SNAA043A – October 2007 – Revised May 2013
AN-1622 LM49100 Evaluation Board»
1
Quick Start Guide
1. Connect the I2C signal generation and interface board to a computer’s parallel port.
2. Apply 2.7V to 5.5V power supply’s positive output to the “VDD” pin on jumper “VDD GND”. Connect
the power supply’s ground return to the “GND” pin also on the aforementioned jumper.
3. Connect the supplied 6-wire (one pin is a No Connect) cable between the I2C signal generation and
interface board and the 6-pin connector (I2C Interface; one pin is a No Connect) on the LM49100
demonstration board. If logic levels other than those set by VDD are required, jumper J1 needs to be
connected and a separate supply applied to the 2–pin header with the I2CVDD pin, with respect to
ground.
4. Headphone amplifier output mode: Apply a stereo input audio signal to jumpers Left Input and Right
Input. Apply the sources’ +input pins and GND pins, respectively, to the demonstration board.
5. Connect a load (≥16Ω) to header HPL (left headphone) and another load (≥16Ω) to header HPR (right
headphone). The HPL pin and HPR pin carries the output signals from the two amplifiers, and each of
the other pins connecting to ground making this configuration single-ended connections.
6. Differential mono amplifier output mode: Apply a mono differential input audio signal to jumper Mono
Input. Apply the sources’ +input and –input to the middle two pins of the 4-pin jumper. The two outer
pins are connected to ground, which are used when the mono input is configured as single-ended
instead of differential.
7. Connect the 32Ω load across the two pins (differential) of the Speaker jumper on the demonstration
board.
8. Apply power. Make measurements. Enjoy the sound.
2
Introduction
To help you investigate and evaluate the LM49100's performance and capabilities, a fully populated
demonstration board is available from the Texas Instruments Audio Products Group. This board is shown
in Figure 1. Connected to an external power supply (2.7V to 5.5V), a signal source and an I2C controller
(or signal source), the LM49100 demonstration board easily demonstrate the amplifier's features.
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General Description
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Figure 1. LM49100 Demonstration Board
3
General Description
The LM49100 is a fully integrated audio subsystem capable of delivering 1.275W of continuous average
power into a mono 8Ω bridged-tied load (BTL) with 1% THD + N and with a 5V power supply. The
LM49100 also has a stereo true-ground headphone amplifier capable of 50mW per channel of continuous
average power into a 32Ω single-ended (SE) loads with 1% THD + N.
The LM49100 has three input channels. One pair of SE inputs can be used with a stereo signal. The other
input channel is fully differential and may be used with a mono input signal. The LM49100 features a 32step digital volume control and ten distinct output modes. The mixer, volume control, and device mode
select are controlled through an I2C compatible interface.
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.
4
Operating Conditions
Temperature Range
TMIN ≤ TA ≤ TMAX
2
−40°C ≤ TA ≤ +85°C
Supply Voltage VDDLS
2.7V ≤ VDDLS ≤ 5.5V
Supply Voltage VDDHP
2.4 V ≤ VDDHP ≤ 2.9V
I2C Voltage (VDDI2C )
1.7V ≤ VDDI2C ≤ 5.5V
VDDHP ≤ VDDLS
VDDI2C ≤ VDDLS
Temperature Range
–40°C ≤ TA ≤ 85°C
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Board Features
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5
Board Features
The LM49100 demonstration board has all of the necessary connections, using 0.100” headers, to apply
the power supply voltage, the audio input signals, and the I2C signal inputs. The amplified audio signal is
available on both a stereo headphone jack and auxiliary output connections.
Also included with the demonstration board is an I2C signal generation board and software. With this
board and the software, the user can easily control the LM49100’s, shutdown function, mute, and stereo
volume control. Figure 2 shows the software’s graphical user interface.
Figure 2. LM49100 Software User's Interface
6
Schematic
Figure 3 shows the LM49100 Demonstration Board schematic. Refer to Table 1 for a list of the
connections and their functions.
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Connections
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VDD
+
VDD
Audio
Input
CIN
1 PF
CIN
1 PF
Audio
Input
Class AB
+6 dB
Mono Input
-60 dB - +12 dB
MINN
0.22 PF
LIN
RIN
2
VDDI C
LS-
GND
Mixer
&
Mode Select
Left Input
-54 dB - +18 dB
0 dB
-12 dB
-18 dB
-24 dB
HPL
Right Input
-54 dB - +18 dB
0 dB
-12 dB
-18 dB
-24 dB
Bias
Click/Pop
Suppresion
BYPASS
+
VDDLS
LS+
0.22 PF
CIN
0.1 PF
MINP
Audio
Input
CIN
2.2 PF
CB
HPR
GNDS
VDDHP
2.2 PF
VDDCP
2
VDDI C
VDDCP
2
SDA
I2C
BUS
Charge Pump
I C
Interface
SCL
ADDR
VIH
GND
VSSHP
VSSCP
C1N
C1
+
C1P
4.7 PF
0.1 PF
GNDCP
CAVSS
VIL
2.2 PF
2.2 PF
Figure 3. LM49100 Demonstration Board Schematic
7
Connections
Connecting to the world is accomplished through the 0.100” headers on the LM49100 demonstration
board. The functions of the different headers are detailed in Table 1.
Table 1. LM49100 Demonstration Board Connections
Header or Jumper Designation
VDD/GND
VDDHP/GND
Headphone power supply for the headphone amplifier which creates split supplies: for the
positive voltage is converted by switch capacitor creating a negative voltage of equal
magnitude.
J1
A shorted J1 connects VDD directly to I2CVDD. An opened J1 disconnects VDD and I2CVDD. If
open, a separate power supply connected to I2CVDD/GND header must be applied.
I2CVDD
Right Input
Left Input
Mono Input
Address Setting
4
Function or Use
Main power supply and ground for the demonstration board.
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Header to apply an independent I2C power supply when J1 is open.
This is the connection to the amplifier’s single-ended right channel input.
This is the connection to the amplifier’s single-ended left channel input.
This is the connection to the amplifier’s differential or single-ended left/right mono input.
The center two pins are the differential inputs, or single-ended inputs, while the outside
pins are the grounds.
Used to set the address of the device. Normally set at “Low” on the demonstration board.
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Power Supply Sequencing
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Table 1. LM49100 Demonstration Board Connections (continued)
Header or Jumper Designation
8
Function or Use
I2C Interface
This is the input connection for the I2C serial clock and serial data signals. The
demonstration board has an adjacent I2C label identifying each pin.
Speaker
Two-pin header used to connect the “+” and “-“ terminals of the mono speaker.
HPR
This is the connection to the amplifier’s single-ended, ground referenced right channel
output. The “HPR” label refers to the output pin and “GND” is the corresponding ground.
HPL
This is the connection to the amplifier’s single-ended, ground referenced left channel
output. The “HPL” label refers to the output pin and “GND” is the corresponding ground.
Power Supply Sequencing
The LM49100 uses two power supply voltages: VDD for the analog circuitry and I2CVDD, which defines the
digital control logic high voltage level. To ensure proper functionality, apply VDD first, followed by I2CVDD. If
one power supply is used, VDD and I2CVDD can be connected together. The part will power-up with both
channels shutdown, the volume control set to minimum, and the mute function active.
9
I2C Signal Generation Board and Software
The I2C signal generation and interface board, along with the LM49100 software, will generate the address
byte and the data byte used in the I2C control data transaction. To use the I2C signal generation and
interface board, please plug it into a PC’s parallel port (on either a notebook or a desktop computer).
The software comes with an installer. To install, unzip the file titled “LM49100_Software.” After the file
unzips, double-click the “setup.exe” file. After it launches, follow the installer’s instructions. Setup will
create a folder named “LM49100” in the “Program” folder on the “C” disk (if the default is used) along with
a shortcut of the same name in the “Programs” folder in the “Start” menu.
The LM49100 program includes controls for the amplifier’s volume control, individual channel shutdown,
and the mute function. The control program's on-screen user interface is shown in Figure 2.
The Default button is used to return the LM49100 to its power-on reset state: minimum volume setting,
shutdown on both amplifiers active, and mute active.
The LM49100’s stereo VOLUME CONTROL has 32 steps and a gain range of –76dB to 18dB. It is
controlled using the slider located at the bottom of the program’s window. Each time the slider is moved
from one tick mark to another, the program updates the amplifier’s volume control.
LEFT CHANNEL, BOTH CHANNELS, and RIGHT CHANNEL controls each have two buttons. For the
left and right channel control, the “ON” button activates its respective channel, whereas the “OFF” button
places its respective channel in shutdown mode. Selecting the BOTH CHANNELS “ON” button
simultaneously activates both channels, whereas selecting the “OFF” button places channels in shutdown
mode.
10
PCB Layout Guidelines
This section provides general practical guidelines for PCB layouts that use various power and ground
traces. Designers should note that these are only "rule-of-thumb" recommendations and the actual results
are predicated on the final layout.
10.1 Power and Ground Circuits
Star trace routing techniques (returning individual traces back to a central point rather than daisy chaining
traces together in a serial manner) can have a major positive impact on low-level signal performance. Star
trace routing refers to using individual traces that radiate from a signal point to feed power and ground to
each circuit or even device. This technique may require greater design time, but should not increase the
final price of the board.
For good THD + N and low noise performance and to ensure correct power-on behavior at the maximum
allowed supply voltage, a local 2.2μF power supply bypass capacitor should be connected as physically
close as possible to the VDDLS pin.
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Bill of Materials
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10.2 Avoiding Typical Design/Layout Problems
Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same
PCB layer. When traces must cross over each other, do so at 90 degrees. Running digital and analog
traces at 90 degrees to each other from the top to the bottom side as much as possible will minimize
capacitive noise coupling and crosstalk.
11
Bill of Materials
Designator
Part Description
Value
Package Type
C1
Tantalum Capacitor
2.2μF
1206
CAVSS
Tantalum Capacitor
2.2μF
1206
CBYPASS
Tantalum Capacitor
2.2μF
1206
CCPUMP1
Tantalum Capacitor
4.7μF
1206
CCPUMP2
Multilayer Ceramic Capacitor
0.1μF
0805
CINL
Multilayer Ceramic Capacitor
0.22μF
0805
CINR
Multilayer Ceramic Capacitor
2.2μF
0805
CMINN
Multilayer Ceramic Capacitor
1μF
0805
CMINP
Multilayer Ceramic Capacitor
1μF
0805
1206
CSUPPLY1
Tantalum Capacitor
2.2μF
CSUPPLY2
Multilayer Ceramic Capacitor
0.1μF
Manufacturer
Manufacturer's
Part Number
Texas Instruments
LM49100
0805
HPL
2–pin header, 100 mil pitch
1x2 Header
HPR
2–pin header, 100 mil pitch
1x2 Header
I2C 6–pin
Header
6–pin header, 100 mil pitch
2x3 Header
Left Input
2–pin header, 100 mil pitch
1x2 Header
Mono Input
4–pin header, 100 mil pitch
1x2 Header
Right Input
2–pin header, 100 mil pitch
1x2 Header
Speaker
2–pin header, 100 mil pitch
1x2 Header
Stereo
Headphone Jack
Headphone Jack
12
VDD
2–pin header, 100 mil pitch
U1
Mono Class AB Audio Subsystem
with a True-Ground Headphone
Amplifier
1x2 Header
Demonstration Board PCB Layout
NOTE: The LM49100 is controlled through an I2C compatible interface. The I2C chip address is 0xF8
(ADR pin = 0) or 0xFAh (ADDR pin = 1).
Figure 4 through Figure 9 show the different layers used to create the LM49100 four-layer demonstration
board. Figure 4 is the silkscreen that shows parts location, Figure 5 is the top layer, Figure 6 is the upper
inner layer, Figure 7 is the lower middle layer, Figure 8 is the bottom layer, and Figure 9 is the bottom
silkscreen layer.
6
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Demonstration Board PCB Layout
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Figure 4. Top Overlay
Figure 5. Top Layer
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Demonstration Board PCB Layout
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Figure 6. Upper Inner Layer
Figure 7. Lower Middle Layer
8
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Demonstration Board PCB Layout
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Figure 8. Bottom Layer
Figure 9. Bottom Overlay
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Typical Demonstration Board Audio Performance
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Typical Demonstration Board Audio Performance
Typical THD + N versus Frequency performance curves at VDD = 3.6V, 3V, and 5V for 8Ω and 32Ω are
shown in Figure 10 through Figure 15, respectively. Typical THD + N versus Output Power performance
curves at VDD = 3V, 3.6V, and 5V for 32Ω and 8Ω are shown in Figure 16 and Figure 17, respectively.
10
10
1
THD+N (%)
THD+N (%)
1
0.1
0.1
0.01
0.01
0.001
20
200
2k
0.001
20
20k
FREQUENCY (Hz)
10
1
THD+N (%)
THD+N (%)
1
0.1
0.1
0.01
0.01
0.001
200
2k
20
20k
FREQUENCY (Hz)
2k
20k
Figure 13. THD+N vs Frequency
VDD = 3V, RL = 32Ω, PO = 25mW
BW = 22kHz, HP, Mode 4, 7
10
10
1
1
THD+N (%)
THD+N (%)
200
FREQUENCY (Hz)
Figure 12. THD+N vs Frequency
VDD = 3V, RL = 8Ω, PO = 215mW
BW = 22kHz, LS, Mode 1
0.1
0.01
0.1
0.01
200
2k
20k
0.001
20
Figure 14. THD+N vs Frequency
VDD = 5V, RL = 8Ω, PO = 630mW
BW = 22kHz, Loudspeaker, Mode 1
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200
2k
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
10
20k
Figure 11. THD+N vs Frequency
VDD = 3.6V, RL = 32Ω, PO = 25mW
BW = 22kHz, HP, Mode 4, 7
10
0.001
20
2k
FREQUENCY (Hz)
Figure 10. THD+N vs Frequency
VDD = 3.6V, RL = 8Ω, PO = 320mW
BW = 22kHz, LS, Mode 1
0.001
20
200
Figure 15. THD+N vs Frequency
VDD = 5V, RL = 32Ω, PO = 25mW
BW = 22kHz, Headphone, Mode 4, 7
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Typical Demonstration Board Audio Performance
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10
10
+3.6V
+3V
+5V
+3V
+3.6V
1
+5V
0.1
THD+N (%)
THD+N (%)
1
0.1
0.01
1
2
5
10
20
50
100
0.01
10
Figure 16. THD+N vs Output Power
RL = 32Ω, f = 1kHz
BW = 22kHz, HP, Mode 4
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100
1000
10000
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 17. THD+N vs Output Power
RL = 8Ω, f = 1kHz
BW = 22kHz, LS , Mode 1
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11
LM49100 Control Tables
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LM49100 Control Tables
NOTE: The LM49100 is controlled through an I2C compatible interface. The I2C chip address is 0xF8
(ADR pin = 0) or 0xFAh (ADDR pin = 1).
Table 2. I2C Control Register Table
D7
D6
D5
D4
D3
D2
D1
D0
Modes Control
0
0
1
1
MC3
MC2
MC1
MC0
HP Volume (Gain)
Control
0
1
INPUT_MUTE
0
0
HPR_SD
HPVC1
HPVC0
Mono Volume
Control
1
0
0
MV4
MV3
MV2
MV1
MV0
Left Volume (Gain)
Control
1
1
0
LV4
LV3
LV2
LV1
LV0
Right Volume (Gain)
Control
1
1
1
RV4
RV3
RV2
RV1
RV0
Table 3. Headphone Attenuation Control (1)
(1)
Gain Select
HPVC1
HPVC0
Gain, dB
0
0
0
0
1
0
1
−12
2
1
0
−18
3
1
1
−24
These bits have added for extra headphone output attenuation.
Table 4. Output Mode Selection (1)
(1)
12
Output
Mode
Number
MC3
MC2
MC1
MC0
0
0
0
0
1
0
0
0
2
0
0
1
3
0
0
1
4
0
1
5
0
6
7
Handsfree Mono Output
Right HP Output
Left HP Output
0
SD
SD
SD
1
2 × GM × M
SD
SD
0
SD
GHP × (GM × M)
GHP × (GM × M)
1
2 × (GL × L + GR × R)
SD
SD
0
0
SD
GHP × (GR × R)
GHP × (GL × L)
1
0
1
2 × (GL × L + GR × R +
GM × M)
SD
SD
0
1
1
0
SD
GHP × (GR × R + GM × M)
GHP × (GL × L + GM × M)
0
1
1
1
2 × (GL × L + GR × R)
GHP × (GR × R)
GHP × (GL × L)
10
1
0
1
0
2 × (GL × L + GR × R)
GHP × (GM × M)
GHP × (GM × M)
14
1
1
1
0
2 × (GL × L + GR × R)
GHP × (GR × R + GM × M)
GHP × (GL × L + GM × M)
GL= Left channel gain; GR = Right channel gain; GM = Mono channel gain; GHP = Headphone Amplifier gain;
R = Right input signal; L = Left input signal; SD = Shutdown; M = Mono input signal
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LM49100 Control Tables
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Table 5. Mono/Stereo Left/Stereo Right Input Gain Control
Volume Step
MV4/LV4/RV4
MV3/LV3/RV3
MV2/LV2/RV2
MV1/LV1/RV1
MV0/LV0/RV0
R/L Gain
(dB)
MonoGain
(dB)
1
0
0
0
0
0
−54
−60
2
0
0
0
0
1
−47
−53
3
0
0
0
1
0
−40.5
−46.5
4
0
0
0
1
1
−34.5
−40.5
5
0
0
1
0
0
−30.0
−36
6
0
0
1
0
1
−27
−33
7
0
0
1
1
0
−24
−30
8
0
0
1
1
1
−21
−27
9
0
1
0
0
0
−18
−24
10
0
1
0
0
1
−15
−21
11
0
1
0
1
0
−13.5
−19.5
12
0
1
0
1
1
−12
−18
13
0
1
1
0
0
−10.5
−16.5
14
0
1
1
0
1
−9
−15
15
0
1
1
1
0
−7.5
−13.5
16
0
1
1
1
1
−6
−12
17
1
0
0
0
0
−4.5
−10.5
18
1
0
0
0
1
−3
−9
19
1
0
0
1
0
−1.5
−7.5
20
1
0
0
1
1
0
−6
21
1
0
1
0
0
1.5
−4.5
22
1
0
1
0
1
3
−3
23
1
0
1
1
0
4.5
−1.5
24
1
0
1
1
1
6
0
25
1
1
0
0
0
7.5
1.5
26
1
1
0
0
1
9
3
27
1
1
0
1
0
10.5
4.5
28
1
1
0
1
1
12
6
29
1
1
1
0
0
13.5
7.5
30
1
1
1
0
1
15
9
31
1
1
1
1
0
16.5
10.5
32
1
1
1
1
1
18
12
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Application Information
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Application Information
15.1 Minimizing Click and Pop
To minimize the audible click and pop heard through a headphone, maximize the input signal through the
corresponding volume (gain) control registers and adjust the output amplifier gain accordingly to achieve
the your desired signal gain. For example, setting the output of the headphone amplifier to -24dB and
setting the input volume control gain to 24dB will reduce the output offset from 7mV (typical) to 2.2mV
(typical). This will reduce the audible click and pop noise significantly while maintaining a 0dB signal gain.
15.2 Signal Ground Noise
The LM49100 has proprietary suppression circuitry, which provides an additional -50dB (typical)
attenuation of the headphone ground noise and its incursion into the headphone. For optimum utilization
of this feature, the headphone jack ground should connect to the AGND (E3) bump.
HPL
HPR
AGND
Figure 18. Suppression Circuitry
15.3 I2C Pin Description
SDA: This is the serial data input pin.
SCL: This is the clock input pin.
ADDR: This is the address select input pin.
15.4 I2C Compatible Interface
The LM49100 uses a serial bus which conforms to the I2C protocol to control the chip's functions with two
wires: clock (SCL) and data (SDA). The clock line is uni-directional. The data line is bi-directional (opencollector). The LM49100's I2C compatible interface supports standard (100kHz) and fast (400kHz) I2C
modes. In this discussion, the master is the controlling microcontroller and the slave is the LM49100.
The I2C address for the LM49100 is determined using the ADDR pin. The LM49100's two possible I2C chip
addresses are of the form 111110X10 (binary), where X1 = 0, if ADDR pin is logic LOW; and X1 = 1, if
ADDR pin is logic HIGH. If the I2C interface is used to address a number of chips in a system, the
LM49100's chip address can be changed to avoid any possible address conflicts.
The bus format for the I2C interface is shown in Figure 19 and the timing diagram is shown in Figure 20.
The bus format diagram is broken up into six major sections:
• The "start" signal is generated by lowering the data signal while the clock signal is HIGH. The start
signal will alert all devices attached to the I2C bus to check the incoming address against their own
address.
• The 8-bit chip address is sent next, most significant bit first. The data is latched in on the rising edge of
the clock. Each address bit must be stable while the clock level is HIGH.
• After the last bit of the address bit is sent, the master releases the data line HIGH (through a pull-up
resistor). Then the master sends an acknowledge clock pulse. If the LM49100 has received the
address correctly, then it holds the data line LOW during the clock pulse. If the data line is not held
LOW during the acknowledge clock pulse, then the master should abort the rest of the data transfer to
the LM49100.
• The 8 bits of data are sent next, most significant bit first. Each data bit should be valid while the clock
level is stable HIGH.
14
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•
•
•
After the data byte is sent, the master must check for another acknowledge to determine if the
LM49100 received the data.
If the master has more data bytes to send to the LM49100, then the master can repeat the previous
two steps until all data bytes have been sent.
The "stop" signal ends the transfer. To signal "stop", the data signal goes HIGH while the clock signal
is HIGH. The data line should be held HIGH when not in use.
Figure 19. I2C Bus Format
Figure 20. I2C Timing Diagram
15.5 I2C Interface Power Supply Pin (VDDI2C)
The LM49100's I2C interface is powered up through theVDD I2C pin. The LM49100's I2C interface operates
at a voltage level set by the VDD I2C pin which can be set independent to that of the main power supply pin
VDD. This is ideal whenever logic levels for the I2C interface are dictated by a microcontroller or
microprocessor that is operating at a lower supply voltage than the main battery of a portable system.
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15.6 PCB Layout and Supply Regulation Considerations for Driving 8Ω Load
Power dissipated by a load is a function of the voltage swing across the load and the load's impedance.
As load impedance decreases, load dissipation becomes increasingly dependent on the interconnect
(PCB trace and wire) resistance between the amplifier output pins and the load's connections. Residual
trace resistance causes a voltage drop, which results in power dissipated in the trace and not in the load
as desired. For example, 0.1Ω trace resistance reduces the output power dissipated by an 8Ω load from
158.3mW to 156.4mW. The problem of decreased load dissipation is exacerbated as load impedance
decreases. Therefore, to maintain the highest load dissipation and widest output voltage swing, PCB
traces that connect the output pins to a load must be as wide as possible.
Poor power supply regulation adversely affects maximum output power. A poorly regulated supply's output
voltage decreases with increasing load current. Reduced supply voltage causes decreased headroom,
output signal clipping, and reduced output power. Even with tightly regulated supplies, trace resistance
creates the same effects as poor supply regulation. Therefore, making the power supply traces as wide as
possible helps maintain full output voltage swing.
15.7 Bridge Configuration Explanation
The LM49100 drives a load, such as a loudspeaker, connected between outputs, LS+ and LS-.
This results in both amplifiers producing signals identical in magnitude, but 180° out of phase. Taking
advantage of this phase difference, a load is placed between LS- and LS+ and driven differentially
(commonly referred to as ”bridge mode”).
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a
single amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage
over the single-ended configuration: its differential output doubles the voltage swing across the load.
Theoretically, this produces four times the output power when compared to a single-ended amplifier under
the same conditions. This increase in attainable output power assumes that the amplifier is not current
limited and that the output signal is not clipped.
Another advantage of the differential bridge output is no net DC voltage across the load. This is
accomplished by biasing LS- and LS+ outputs at half-supply. This eliminates the coupling capacitor that
single supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a typical singleended configuration forces a single-supply amplifier's half-supply bias voltage across the load. This
increases internal IC power dissipation and may permanently damage loads such as loudspeakers.
15.8 Power Dissipation
Power dissipation is a major concern when designing a successful single-ended or bridged amplifier.
A direct consequence of the increased power delivered to the load by a bridge amplifier is higher internal
power dissipation. The LM49100 has a pair of bridged-tied amplifiers driving a handsfree loudspeaker, LS.
The maximum internal power dissipation operating in the bridge mode is twice that of a single-ended
amplifier. From Equation 1, assuming a 5V power supply and an 8Ω load, the maximum MONO power
dissipation is 634mW.
PDMAX-LS = 4(VDD)2/ (2π2 RL): Bridge Mode
(1)
The LM49100 also has a pair of single-ended amplifiers driving stereo headphones, HPR and HPL. The
maximum internal power dissipation for HPR and HPL is given by Equation 2. Assuming a 2.8V power
supply and a 32Ω load, the maximum power dissipation for LOUT and ROUT is 49mW, or 99mW total.
PDMAX-HPL = 4(VDDHP)2 / (2π2 RL): Single-ended Mode
(2)
The maximum internal power dissipation of the LM49100 occurs when all three amplifiers pairs are
simultaneously on; and is given by:
PDMAX-TOTAL = PDMAX-LS + PDMAX-HPL + PDMAX-HPR
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(3)
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The maximum power dissipation point given by Equation 3 must not exceed the power dissipation given
by:
PDMAX = (TJMAX - TA) / θJA
(4)
The LM49100's TJMAX = 150°C. In the csBGA package, the LM49100's θJA is 50.2°C/W. At any given
ambient temperature TA, use Equation 4 to find the maximum internal power dissipation supported by the
IC packaging. Rearranging Equation 4 and substituting PDMAX-TOTAL for PDMAX results in Equation 5. This
equation gives the maximum ambient temperature that still allows maximum stereo power dissipation
without violating the LM49100's maximum junction temperature.
TA = TJMAX - PDMAX-TOTAL θJA
(5)
For a typical application with a 5V power supply and an 8Ω load, the maximum ambient temperature that
allows maximum mono power dissipation without exceeding the maximum junction temperature is
approximately 114°C for the csBGA package.
Equation 6 gives the maximum junction temperature TJMAX. If the result violates the LM49100's 150°C,
reduce the maximum junction temperature by reducing the power supply voltage or increasing the load
resistance. Further allowance should be made for increased ambient temperatures.
TJMAX = PDMAX-TOTAL θJA + TA
(6)
The previous examples assume that a device is a surface mount part operating around the maximum
power dissipation point. Since internal power dissipation is a function of output power, higher ambient
temperatures are allowed as output power or duty cycle decreases. If the result of Equation 3 is greater
than that of Equation 4, then decrease the supply voltage, increase the load impedance, or reduce the
ambient temperature. If these measures are insufficient, a heat sink can be added to reduce θJA. The heat
sink can be created using additional copper area around the package, with connections to the ground
pin(s), supply pin and amplifier output pins.
15.9 Power Supply Bypassing
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power
supply rejection. Applications that employ a 5V regulator typically use a 1µF in parallel with a 0.1µF filter
capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's
transient response. However, their presence does not eliminate the need for a local 4.7µF tantalum
bypass capacitor and a parallel 0.1µF ceramic capacitor connected between the LM49100's supply pin
and ground. Keep the length of leads and traces that connect capacitors between the LM49100's power
supply pin and ground as short as possible.
15.10 Selecting External Components
15.10.1 Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value input coupling capacitor (CIN in Figure 1). A
high value capacitor can be expensive and may compromise space efficiency in portable designs. In many
cases, however, the loudspeakers used in portable systems, whether internal or external, have little ability
to reproduce signals below 150Hz. Applications using loudspeakers and headphones with this limited
frequency response reap little improvement by using large input capacitor.
The internal input resistor (Ri), typical 12.5kΩ, and the input capacitor (CIN) produce a high pass filter
cutoff frequency that is found using:
fc = 1 / (2πRiCIN)
(7)
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Micro SMD Wafer Level Chip Scale Package: PCB, Layout, and Mounting Considerations
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15.10.2 Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consideration should be paid to value of CB, the
capacitor connected to the BYPASS pin. Since CB determines how fast the LM49100 settles to quiescent
operation, its value is critical when minimizing turn-on pops. Choosing CB equal to 2.2µF along with a
small value of Ci (in the range of 0.1µF to 0.33µF), produces a click-less and pop-less shutdown function.
As discussed above, choosing CIN no larger than necessary for the desired bandwidth helps minimize
clicks and pops. CB's value should be in the range of 4 to 5 times the value of CIN . This ensures that
output transients are eliminated when power is first applied or the LM49100 resumes operation after
shutdown.
16
Micro SMD Wafer Level Chip Scale Package: PCB, Layout, and Mounting
Considerations
Please refer to AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009) for possible updates to the
μSMD package information.
17
Demo Board Schematic
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Revision History
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Revision History
Rev
Date
1.0
10/1907
Description
SNAA043A – October 2007 – Revised May 2013
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