LM4675, LM4675SDBD, LM4675TLBD
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LM4675
SNAS353C – AUGUST 2006 – REVISED MAY 2013
Ultra-Low EMI, Filterless, 2.65W, Mono, Class D
Audio Power Amplifier with Spread Spectrum
Check for Samples: LM4675, LM4675SDBD, LM4675TLBD
FEATURES
DESCRIPTION
•
•
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The LM4675 is a single supply, high efficiency,
2.65W, mono, Class D audio amplifier. A spread
spectrum, filterless PWM architecture reduces EMI
and eliminates the output filter, reducing external
component count, board area consumption, system
cost, and simplifying design.
1
2
Spread Spectrum Architecture Reduces EMI
Mono Class D Operation
No Output Filter Required for Inductive Loads
Externally Configurable Gain
Very Fast Turn On Time: 17μs (typ)
Minimum External Components
"Click and Pop" Suppression Circuitry
Micro-Power Shutdown Mode
Available in Space-Saving 0.5mm Pitch
DSBGA and WSON Packages
APPLICATIONS
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Mobile Phones
PDAs
Portable Electronic Devices
KEY SPECIFICATIONS
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Efficiency at 3.6V, 400mW into 8Ω Speaker:
89% (typ)
Efficiency at 3.6V, 100mW into 8Ω Speaker:
80% (typ)
Efficiency at 5V, 1W into 8Ω Speaker: 89%
(typ)
Quiescent Current, 3.6V Supply: 2.2mA (typ)
Total Shutdown Power Supply Current: 0.01µA
(typ)
Single Supply Range: 2.4V to 5.5V
PSRR, f = 217Hz: 82dB
The LM4675 is designed to meet the demands of
mobile phones and other portable communication
devices. Operating on a single 5V supply, it is
capable of driving a 4Ω speaker load at a continuous
average output of 2.2W with less than 1% THD+N. Its
flexible power supply requirements allow operation
from 2.4V to 5.5V. The wide band spread spectrum
architecture of the LM4675 reduces EMI-radiated
emissions due to the modulator frequency.
The LM4675 has high efficiency with speaker loads
compared to a typical Class AB amplifier. With a 3.6V
supply driving an 8Ω speaker, the IC's efficiency for a
100mW power level is 80%, reaching 89% at 400mW
output power.
The LM4675 features a low-power consumption
shutdown mode. Shutdown may be enabled by
driving the Shutdown pin to a logic low (GND).
The gain of the LM4675 is externally configurable
which allows independent gain control from multiple
sources by summing the signals. Output short circuit
and thermal overload protection prevent the device
from damage during fault conditions.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006–2013, Texas Instruments Incorporated
LM4675, LM4675SDBD, LM4675TLBD
SNAS353C – AUGUST 2006 – REVISED MAY 2013
www.ti.com
50
FCC Class B Limit
AMPLITUDE (dbmV/m)
45
40
35
30
LM4675TL Output Spectrum
25
20
15
30
60
80
100 120 140 160 180
200 220 240 260 280 300
FREQUENCY (MHz)
Figure 1. LM4675 Rf Emissions — 6in cable
Typical Application
CS
4.7 PF
VDD
+
VDD
Input
Ri
PVDD
Internal
Oscillator
-IN
VO2
-
Spread Spectrum
PWM Modulator
+
Ri
Shutdown
Control
FET
Drivers
VO1
+IN
Shutdown
Click/Pop
Suppression
Bias
Circuit
GND
PGND
Figure 2. Typical Audio Amplifier Application Circuit
2
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SNAS353C – AUGUST 2006 – REVISED MAY 2013
Connection Diagrams
xxx
GND
IN+
A
Vo1
VDD
B
PGND
IN-
C
Vo2
1
2
SHUTDOWN
Figure 4. 8-Pin WSON - Top View
See NGQ0008A Package
3
PVDD
Figure 3. 9-Bump DSBGA - Top View
See YZR0009 Package
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings (1) (2) (3)
Supply Voltage (1)
6.0V
−65°C to +150°C
Storage Temperature
VDD + 0.3V ≥ V ≥ GND - 0.3V
Voltage at Any Input Pin
Power Dissipation
(4)
Internally Limited
ESD Susceptibility, all other pins (5)
2.0kV
ESD Susceptibility (6)
200V
Junction Temperature (TJMAX)
Thermal Resistance
150°C
θJA (DSBGA)
220°C/W
θJA (WSON)
73°C/W
Soldering Information
(1)
(2)
(3)
(4)
(5)
(6)
See (SNVA009) "microSMD Wafers Level Chip Scale
Package."
All voltages are measured with respect to the ground pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature
TA. The maximum allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever
is lower. For the LM4675, TJMAX = 150°C. The typical θJA is 99.1°C/W for the DSBGA package.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF – 240pF discharged through all pins.
Operating Ratings (1) (2)
Temperature Range TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ 85°C
2.4V ≤ VDD ≤ 5.5V
Supply Voltage
(1)
(2)
All voltages are measured with respect to the ground pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
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Electrical Characteristics (1) (2)
The following specifications apply for AV = 2V/V (RI = 150kΩ), RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits
apply for TA = 25°C.
Symbol
Parameter
LM4675
Conditions
Typical (3)
Limit (4) (5)
Units
(Limits)
|VOS|
Differential Output Offset
Voltage
VI = 0V, AV = 2V/V,
VDD = 2.4V to 5.0V
|IIH|
Logic High Input Current
VDD = 5.0V, VI = 5.5V
17
100
μA (max)
|IIL|
Logic Low Input Current
VDD = 5.0V, VI = –0.3V
0.9
5
μA (max)
VIN = 0V, No Load, VDD = 5.0V
2.8
3.9
mA (max)
VIN = 0V, No Load, VDD = 3.6V
2.2
2.9
mA
VIN = 0V, No Load, VDD = 2.4V
1.6
2.3
mA (max)
VIN = 0V, RL = 8Ω, VDD = 5.0V
2.8
VIN = 0V, RL = 8Ω, VDD = 3.6V
2.2
VIN = 0V, RL = 8Ω, VDD = 2.4V
1.6
VSHUTDOWN = 0V
VDD = 2.4V to 5.0V
0.01
1.0
μA (max)
Quiescent Power Supply
Current
IDD
3
mV
ISD
Shutdown Current (6)
VSDIH
Shutdown voltage input high
1.4
V (min)
VSDIL
Shutdown voltage input low
0.4
V (max)
ROSD
Output Impedance
VSHUTDOWN = 0.4V
AV
Gain
RSD
Resistance from Shutdown Pin
to GND
fSW
Switching Frequency
RL = 15μH + 4Ω + 15μH
THD = 10% (max)
f = 1kHz, 22kHz BW
RL = 15μH + 4Ω + 15μH
THD = 1% (max)
f = 1kHz, 22kHz BW
PO
Output Power
RL = 15μH + 8Ω + 15μH
THD = 10% (max)
f = 1kHz, 22kHz BW
RL = 15μH + 8Ω + 15μH
THD = 1% (max)
f = 1kHz, 22kHz BW
VDD = 5V
(1)
(2)
(3)
(4)
(5)
(6)
4
Total Harmonic Distortion +
Noise
kΩ
300kΩ/RI
V/V (min)
V/V (max)
300
kΩ
300±30%
kHz
2.7
W
VDD = 3.6V
1.3
W
VDD = 2.5V
560
mW
VDD = 5V
2.2
W
VDD = 3.6V
1.08
W
VDD = 2.5V
450
mW
VDD = 5V
1.6
W
VDD = 3.6V
820
mW
VDD = 2.5V
350
mW
VDD = 5V
1.3
VDD = 3.6V
650
VDD = 2.5V
THD+N
100
W
600
mW
290
mW
VDD = 5V, PO = 0.1W, f = 1kHz
0.03
%
VDD = 3.6V, PO = 0.1W, f = 1kHz
0.02
%
VDD = 2.5V, PO = 0.1W, f = 1kHz
0.04
%
All voltages are measured with respect to the ground pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
Typical specifications are specified at 25°C and represent the parametric norm.
Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. The
Shutdown pin should be driven as close as possible to GND for minimal shutdown current and to VDD for the best THD performance in
PLAY mode. See the Application Information section under SHUTDOWN FUNCTION for more information.
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SNAS353C – AUGUST 2006 – REVISED MAY 2013
Electrical Characteristics(1)(2) (continued)
The following specifications apply for AV = 2V/V (RI = 150kΩ), RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits
apply for TA = 25°C.
Symbol
PSRR
SNR
εOUT
Parameter
Power Supply Rejection Ratio
(Input Referred)
Signal to Noise Ratio
Output Noise
(Input Referred)
Limit (4) (5)
Units
(Limits)
82
dB
VRipple = 200mVPP Sine,
fRipple = 1kHz, VDD = 3.6, 5V
Inputs to AC GND, CI = 2μF
80
dB
VDD = 5V, PO = 1WRMS
97
dB
VDD = 3.6V, f = 20Hz – 20kHz
Inputs to AC GND, CI = 2μF
No Weighting
28
μVRMS
VDD = 3.6V, Inputs to AC GND
CI = 2μF, A Weighted
22
μVRMS
80
dB
Common Mode Rejection
Ratio
(Input Referred)
VDD = 3.6V, VRipple = 1VPP Sine
fRipple = 217Hz
TWU
Wake-up Time
VDD = 3.6V
TSD
Shutdown Time
Efficiency
Typical (3)
VRipple = 200mVPP Sine,
fRipple = 217Hz, VDD = 3.6, 5V
Inputs to AC GND, CI = 2μF
CMRR
η
LM4675
Conditions
17
μs
140
μs
VDD = 3.6V, POUT = 400mW
RL = 8Ω
89
%
VDD = 5V, POUT = 1W
RL = 8Ω
89
%
External Components Description
(Figure 2)
Components
Functional Description
1.
CS
Supply bypass capacitor which provides power supply filtering. Refer to the POWER SUPPLY BYPASSING section
for information concerning proper placement and selection of the supply bypass capacitor.
2.
CI
Input AC coupling capacitor which blocks the DC voltage at the amplifier's input terminals.
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Typical Performance Characteristics
The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series
with the LC filter on the demo board.
THD + N vs Output Power
f = 1kHz, RL = 8Ω
100
VDD = 5V
10
VDD = 3.6V
THD+N (%)
THD+N (%)
V DD = 5V
10
VDD = 3.6V
V DD = 3.0V
1
THD + N vs Output Power
f = 1kHz, RL = 4Ω
100
VDD = 3.0V
1
0.1
0.1
0.01
0.001
0.01
0.1
1
0.01
0.001
10
0.01
Figure 6.
THD + N vs Frequency
VDD = 2.5V, POUT = 100mW, RL = 8Ω
THD + N vs Frequency
VDD = 3.6V, POUT = 150mW, RL = 8Ω
100
100
10
10
1
0.1
1
0.1
0.01
0.001
10
100
1000
10000
0.001
10
100000
1000
10000
100000
FREQUENCY (Hz)
Figure 7.
Figure 8.
THD + N vs Frequency
VDD = 5V, POUT = 200mW, RL = 8Ω
THD + N vs Frequency
VDD = 2.5V, POUT = 100mW, RL = 4Ω
100
10
10
THD+N (%)
1
0.1
0.01
0.001
10
100
FREQUENCY (Hz)
100
THD+N (%)
10
OUTPUT POWER (W)
0.01
1
0.1
0.01
100
1000
10000
FREQUENCY (Hz)
100000
0.001
10
100
1000
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10000
100000
FREQUENCY (Hz)
Figure 9.
6
1
Figure 5.
THD+N (%)
THD+N (%)
OUTPUT POWER (W)
0.1
Figure 10.
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Typical Performance Characteristics (continued)
The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series
with the LC filter on the demo board.
THD + N vs Frequency
VDD = 5V, POUT = 150mW, RL = 4Ω
100
100
10
10
THD+N (%)
THD+N (%)
THD + N vs Frequency
VDD = 3.6V, POUT = 100mW, RL = 4Ω
1
0.1
0.01
1
0.1
0.01
0.001
10
100
1000
10000
100000
0.001
10
100
FREQUENCY (Hz)
100000
FREQUENCY (Hz)
Figure 12.
Efficiency vs. Output Power
RL = 4Ω, f = 1kHz
Efficiency vs. Output Power
RL = 8Ω, f = 1kHz
100
V DD = 5V
90
90
80
80
70
70
V DD = 2.5V
60
EFFICIENCY (%)
EFFICIENCY (%)
10000
Figure 11.
100
V DD = 3.6V
50
40
30
V DD = 3.6V
V DD = 2.5V
V DD = 5V
60
50
40
30
20
20
10
10
0
0
0
500
1000
1500
0
2000
500
1000
1500
2000
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 13.
Figure 14.
Power Dissipation vs. Output Power
RL = 4Ω, f = 1kHz
Power Dissipation vs. Output Power
RL = 8Ω, f = 1kHz
500
250
POWER DISSIPATION (mW)
POWER DISSIPATION (mW)
1000
400
V DD = 5V
300
V DD = 3.6V
200
V DD = 2.5V
100
200
V DD = 5V
150
V DD = 3.6V
100
V DD = 2.5V
50
0
0
0
500
1000
1500
OUTPUT POWER (mW)
2000
0
250
500
1000
1250
1500
OUTPUT POWER (mW)
Figure 15.
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750
Figure 16.
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Typical Performance Characteristics (continued)
The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series
with the LC filter on the demo board.
Output Power vs. Supply Voltage
RL = 8Ω, f = 1kHz
4
2
3
1.5
OUTPUT POWER (W)
OUTPUT POWER (W)
Output Power vs. Supply Voltage
RL = 4Ω, f = 1kHz
THD+N = 10%
2
THD+N = 1%
1
0
2.5
THD+N = 10%
1
THD+N = 1%
0.5
0
3
3.5
4
4.5
5
5.5
2.5
3
SUPPLY VOLTAGE (V)
5
5.5
Figure 18.
PSRR vs. Frequency
VDD = 3.6V ,VRIPPLE = 200mVP-P, RL = 8Ω
CMRR vs. Frequency
VDD = 3.6V, VCM = 1VP-P, RL = 8Ω
0
0
-10
-10
-20
-20
-30
CMRR(dB)
PSRR (dB)
4.5
SUPPLY VOLTAGE (V)
-40
-50
-60
-40
-50
-60
-70
-70
-80
-80
-90
-90
10
100
1000
10000
-100
10
100000
100
FREQUENCY (Hz)
1000
10000
100000
FREQUENCY (Hz)
Figure 19.
Figure 20.
Supply Current vs. Supply Voltage
No Load
Shutdown Supply Current vs. Supply Voltage
No Load
0.05
SUPPLY CURRENT (PA)
5
4
3
2
0.04
0.03
0.02
0.01
1
0
2.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
5.5
0
2.5
3
3.5
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4
4.5
5
5.5
SUPPLY VOLTAGE (V)
Figure 21.
8
4
Figure 17.
-30
SUPPLY CURRENT (mA)
3.5
Figure 22.
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Typical Performance Characteristics (continued)
The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series
with the LC filter on the demo board.
0 dB
0
Fixed Frequency FFT
VDD = 3.6V
Spread Spectrum FFT
VDD = 3.6V
0 dB
-10
-10
-20
-20
-30
-30
-40
-40
0
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
-100
20 Hz
10 MHz
-100
20 Hz
10 MHz
Figure 23.
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Figure 24.
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APPLICATION INFORMATION
GENERAL AMPLIFIER FUNCTION
The LM4675 features a filterless modulation scheme. The differential outputs of the device switch at 300kHz from
VDD to GND. When there is no input signal applied, the two outputs (VO1 and VO2) switch with a 50% duty cycle,
with both outputs in phase. Because the outputs of the LM4675 are differential, the two signals cancel each
other. This results in no net voltage across the speaker, thus there is no load current during an idle state,
conserving power.
With an input signal applied, the duty cycle (pulse width) of the LM4675 outputs changes. For increasing output
voltages, the duty cycle of VO1 increases, while the duty cycle of VO2 decreases. For decreasing output voltages,
the converse occurs, the duty cycle of VO2 increases while the duty cycle of VO1 decreases. The difference
between the two pulse widths yields the differential output voltage.
SPREAD SPECTRUM MODULATION
The LM4675 features a fitlerless spread spectrum modulation scheme that eliminates the need for output filters,
ferrite beads or chokes. The switching frequency varies by ±30% about a 300kHz center frequency, reducing the
wideband spectral contend, improving EMI emissions radiated by the speaker and associated cables and traces.
Where a fixed frequency class D exhibits large amounts of spectral energy at multiples of the switching
frequency, the spread spectrum architecture of the LM4675 spreads that energy over a larger bandwidth. The
cycle-to-cycle variation of the switching period does not affect the audio reproduction of efficiency.
POWER DISSIPATION AND EFFICIENCY
In general terms, efficiency is considered to be the ratio of useful work output divided by the total energy required
to produce it with the difference being the power dissipated, typically, in the IC. The key here is “useful” work. For
audio systems, the energy delivered in the audible bands is considered useful including the distortion products of
the input signal. Sub-sonic (DC) and super-sonic components (>22kHz) are not useful. The difference between
the power flowing from the power supply and the audio band power being transduced is dissipated in the
LM4675 and in the transducer load. The amount of power dissipation in the LM4675 is very low. This is because
the ON resistance of the switches used to form the output waveforms is typically less than 0.25Ω. This leaves
only the transducer load as a potential "sink" for the small excess of input power over audio band output power.
The LM4675 dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to
act as a heat sink.
DIFFERENTIAL AMPLIFIER EXPLANATION
As logic supply voltages continue to shrink, designers are increasingly turning to differential analog signal
handling to preserve signal to noise ratios with restricted voltage swing. The LM4675 is a fully differential
amplifier that features differential input and output stages. A differential amplifier amplifies the difference between
the two input signals. Traditional audio power amplifiers have typically offered only single-ended inputs resulting
in a 6dB reduction in signal to noise ratio relative to differential inputs. The LM4675 also offers the possibility of
DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The LM4675 can be
used, however, as a single ended input amplifier while still retaining it's fully differential benefits. In fact,
completely unrelated signals may be placed on the input pins. The LM4675 simply amplifies the difference
between the signals. A major benefit of a differential amplifier is the improved common mode rejection ratio
(CMRR) over single input amplifiers. The common-mode rejection characteristic of the differential amplifier
reduces sensitivity to ground offset related noise injection, especially important in high noise applications.
PCB LAYOUT CONSIDERATIONS
As output power increases, interconnect resistance (PCB traces and wires) between the amplifier, load and
power supply create a voltage drop. The voltage loss on the traces between the LM4675 and the load results is
lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4675 has
the same effect as a poorly regulated supply, increased ripple on the supply line also reducing the peak output
power. The effects of residual trace resistance increases as output current increases due to higher output power,
decreased load impedance or both. To maintain the highest output voltage swing and corresponding peak output
power, the PCB traces that connect the output pins to the load and the supply pins to the power supply should
be as wide as possible to minimize trace resistance.
10
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The use of power and ground planes will give the best THD+N performance. While reducing trace resistance, the
use of power planes also creates parasite capacitors that help to filter the power supply line.
The inductive nature of the transducer load can also result in overshoot on one or both edges, clamped by the
parasitic diodes to GND and VDD in each case. From an EMI standpoint, this is an aggressive waveform that can
radiate or conduct to other components in the system and cause interference. It is essential to keep the power
and output traces short and well shielded if possible. Use of ground planes, beads, and micro-strip layout
techniques are all useful in preventing unwanted interference.
As the distance from the LM4675 and the speaker increase, the amount of EMI radiation will increase since the
output wires or traces acting as antenna become more efficient with length. What is acceptable EMI is highly
application specific. Ferrite chip inductors placed close to the LM4675 may be needed to reduce EMI radiation.
The value of the ferrite chip is very application specific.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor (CS) location should be as close as possible to the LM4675. Typical
applications employ a voltage regulator with a 10µF and a 0.1µF bypass capacitors that increase supply stability.
These capacitors do not eliminate the need for bypassing on the supply pin of the LM4675. A 4.7µF tantalum
capacitor is recommended.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4675 contains shutdown circuitry that reduces
current draw to less than 0.01µA. The trigger point for shutdown is shown as a typical value in the Electrical
Characteristics Tables and in the Shutdown Hysteresis Voltage graphs found in the Typical Performance
Characteristics section. It is best to switch between ground and supply for minimum current usage while in the
shutdown state. While the LM4675 may be disabled with shutdown voltages in between ground and supply, the
idle current will be greater than the typical 0.01µA value.
The LM4675 has an internal resistor connected between GND and Shutdown pins. The purpose of this resistor is
to eliminate any unwanted state changes when the Shutdown pin is floating. The LM4675 will enter the shutdown
state when the Shutdown pin is left floating or if not floating, when the shutdown voltage has crossed the
threshold. To minimize the supply current while in the shutdown state, the Shutdown pin should be driven to
GND or left floating. If the Shutdown pin is not driven to GND, the amount of additional resistor current due to the
internal shutdown resistor can be found by Equation 1 below.
(VSD - GND) / 300kΩ
(1)
With only a 0.5V difference, an additional 1.7µA of current will be drawn while in the shutdown state.
PROPER SELECTION OF EXTERNAL COMPONENTS
The gain of the LM4675 is set by the external resistors, Ri in Figure 2, The Gain is given by Equation 2 below.
Best THD+N performance is achieved with a gain of 2V/V (6dB).
AV = 2 * 150 kΩ / Ri
(V/V)
(2)
It is recommended that resistors with 1% tolerance or better be used to set the gain of the LM4675. The Ri
resistors should be placed close to the input pins of the LM4675. Keeping the input traces close to each other
and of the same length in a high noise environment will aid in noise rejection due to the good CMRR of the
LM4675. Noise coupled onto input traces which are physically close to each other will be common mode and
easily rejected by the LM4675.
Input capacitors may be needed for some applications or when the source is single-ended (see Figure 26,
Figure 28). Input capacitors are needed to block any DC voltage at the source so that the DC voltage seen
between the input terminals of the LM4675 is 0V. Input capacitors create a high-pass filter with the input
resistors, Ri. The –3dB point of the high-pass filter is found using Equation 3 below.
fC = 1 / (2πRi Ci )
(Hz)
(3)
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The input capacitors may also be used to remove low audio frequencies. Small speakers cannot reproduce low
bass frequencies so filtering may be desired . When the LM4675 is using a single-ended source, power supply
noise on the ground is seen as an input signal by the +IN input pin that is capacitor coupled to ground (See
Figure 28 – Figure 30). Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a
GSM phone, for example, will filter out this noise so it is not amplified and heard on the output. Capacitors with a
tolerance of 10% or better are recommended for impedance matching.
DIFFERENTIAL CIRCUIT CONFIGURATIONS
The LM4675 can be used in many different circuit configurations. The simplest and best performing is the DC
coupled, differential input configuration shown in Figure 25. Equation 2 above is used to determine the value of
the Ri resistors for a desired gain.
Input capacitors can be used in a differential configuration as shown in Figure 26. Equation 3 above is used to
determine the value of the Ci capacitors for a desired frequency response due to the high-pass filter created by
Ci and Ri. Equation 2 above is used to determine the value of the Ri resistors for a desired gain.
The LM4675 can be used to amplify more than one audio source. Figure 27 shows a dual differential input
configuration. The gain for each input can be independently set for maximum design flexibility using the Ri
resistors for each input and Equation 2. Input capacitors can be used with one or more sources as well to have
different frequency responses depending on the source or if a DC voltage needs to be blocked from a source.
SINGLE-ENDED CIRCUIT CONFIGURATIONS
The LM4675 can also be used with single-ended sources but input capacitors will be needed to block any DC at
the input terminals. Figure 28 shows the typical single-ended application configuration. The equations for Gain,
Equation 2, and frequency response, Equation 3, hold for the single-ended configuration as shown in Figure 28.
When using more than one single-ended source as shown in Figure 29, the impedance seen from each input
terminal should be equal. To find the correct values for Ci3 and Ri3 connected to the +IN input pin the equivalent
impedance of all the single-ended sources are calculated. The single-ended sources are in parallel to each other.
The equivalent capacitor and resistor, Ci3 and Ri3, are found by calculating the parallel combination of all
Civalues and then all Ri values. Equation 4 and Equation 5 below are for any number of single-ended sources.
Ci3 = Ci1 + Ci2 + Cin (F)
Ri3 = 1 / (1/Ri1 + 1/Ri2 + 1/Rin)
(4)
(5)
(Ω)
The LM4675 may also use a combination of single-ended and differential sources. A typical application with one
single-ended source and one differential source is shown in Figure 30. Using the principle of superposition, the
external component values can be determined with the above equations corresponding to the configuration.
Figure 25. Differential Input Configuration
12
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Figure 26. Differential Input Configuration with Input Capacitors
Figure 27. Dual Differential Input Configuration
Figure 28. Single-Ended Input Configuration
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Figure 29. Dual Single-Ended Input Configuration
Figure 30. Dual Input with a Single-Ended Input and a Differential Input
14
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SNAS353C – AUGUST 2006 – REVISED MAY 2013
REFERENCE DESIGN BOARD SCHEMATIC
In addition to the minimal parts required for the application circuit, a measurement filter is provided on the
evaluation circuit board so that conventional audio measurements can be conveniently made without additional
equipment. This is a balanced input, grounded differential output low pass filter with a 3dB frequency of
approximately 35kHz and an on board termination resistor of 300Ω (see schematic). Note that the capacitive load
elements are returned to ground. This is not optimal for common mode rejection purposes, but due to the
independent pulse format at each output there is a significant amount of high frequency common mode
component on the outputs. The grounded capacitive filter elements attenuate this component at the board to
reduce the high frequency CMRR requirement placed on the analysis instruments.
Even with the grounded filter the audio signal is still differential, necessitating a differential input on any analysis
instrument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential
responding because the ring of the BNC is usually grounded.
The commonly used Audio Precision analyzer is differential, but its ability to accurately reject high frequency
signals is questionable necessitating the on board measurement filter. When in doubt or when the signal needs
to be single-ended, use an audio signal transformer to convert the differential output to a single ended output.
Depending on the audio transformer's characteristics, there may be some attenuation of the audio signal which
needs to be taken into account for correct measurement of performance.
Measurements made at the output of the measurement filter suffer attenuation relative to the primary, unfiltered
outputs even at audio frequencies. This is due to the resistance of the inductors interacting with the termination
resistor (300Ω) and is typically about -0.25dB (3%). In other words, the voltage levels (and corresponding power
levels) indicated through the measurement filter are slightly lower than those that actually occur at the load
placed on the unfiltered outputs. This small loss in the filter for measurement gives a lower output power reading
than what is really occurring on the unfiltered outputs and its load.
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REVISION HISTORY
Rev
Date
1.0
08/16/06
Initial release.
Description
1.1
09/01/06
Added the DSBGA (YZR009) package.
1.2
10/12/06
Text edit (X-axis label) on Rf Emissions on page 1.
1.3
07/02/08
Text edits.
Changes from Revision B (May 2013) to Revision C
•
16
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 15
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM4675SD/NOPB
ACTIVE
WSON
NGQ
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
L4675
LM4675SDX/NOPB
ACTIVE
WSON
NGQ
8
4500
RoHS & Green
SN
Level-1-260C-UNLIM
L4675
LM4675TL/NOPB
ACTIVE
DSBGA
YZR
9
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
G
H8
LM4675TLX/NOPB
ACTIVE
DSBGA
YZR
9
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
G
H8
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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