LM48310 [NSC]
Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S; 超低EMI ，无需滤波， 2.6W ，单声道， D类音频功率放大器E2S
| 型号： | LM48310 |
| 厂家： | 
National Semiconductor |
| 描述： | Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S |
| 文件： | 总20页 (文件大小：476K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
March 4, 2008
LM48310ꢀ
Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio
Power Amplifier with E2S
General Description
Key Specifications
The LM48310 is a single supply, high efficiency, mono, 2.6W,
filterless switching audio amplifier. The LM48310 features
National’s Enhanced Emissions Suppression (E2S) system,
that features a unique patent-pending ultra low EMI, spread
spectrum, PWM architecture, that significantly reduces RF
emissions while preserving audio quality and efficiency. The
E2S system improves battery life, reduces external compo-
nent count, board area consumption, system cost, and sim-
plifying design.
■ꢀEfficiency at 3.6V, 400mW into 8Ω
■ꢀEfficiency at 5V, 1W into 8Ω
■ꢀQuiescent Power Supply Current at 5V
■ꢀPower Output at VDD = 5V,
RL = 4Ω, THD+N ≤ 10%
85% (typ)
88% (typ)
3.2mA
2.6W (typ)
■ꢀPower Output at VDD = 5V,
RL = 8Ω, THD+N ≤ 10%
1.6W (typ)
The LM48310 is designed to meet the demands of portable
multimedia devices. Operating from a single 5V supply, the
device is capable of delivering 2.6W of continuous output
power to a 4Ω load with less than 10% THD+N. Flexible power
supply requirements allow operation from 2.4V to 5.5V. The
LM48310 offers two logic selectable modulation schemes,
fixed frequency mode, and an EMI suppressing spread spec-
trum mode. The E2S system includes an advanced, patent-
pending edge rate control (ERC) architecture that further
reduce emissions by minimizing the high frequency compo-
nent of the device output, while maintaining high quality audio
reproduction (THD+N = 0.03%) and high efficiency (η = 88%).
0.01μA (typ)
■ꢀShutdown current
Features
Passes FCC Class B Radiated Emissions with 20 inches
of cable
■
E2S System Reduces EMI while Preserving Audio Quality
and Efficiency
■
Output Short Circuit Protection with Auto-Recovery
Stereo Class D operation
■
■
■
■
■
■
■
■
■
■
No output filter required
The LM48310 also features
a SYNC_IN input and
SYNC_OUT, which allows multiple devices to operate with
the same switching frequency, eliminating beat frequencies
and any other interference caused by clock intermodulation.
Internally Configured Gain (12dB)
Synchronizable Oscillator for Multi-Channel operation
Low power shutdown mode
The LM48310 features high efficiency compared to conven-
tional Class AB amplifiers, and other low EMI Class D ampli-
fiers. When driving and 8Ω speaker from a 5V supply, the
device operates with 88% efficiency at PO = 1W. The gain of
the LM48310 is internally set to 12dB, further reducing exter-
nal component count. A low power shutdown mode reduces
supply current consumption to 0.01μA.
Advanced output short circuit protection with auto-recovery
prevents the device from being damaged during fault condi-
tions. Superior click and pop suppression eliminates audible
transients on power-up/down and during shutdown.
Minimum external components
"Click and pop" suppression
Micro-power shutdown
Available in space-saving LLP package
Applications
Mobile phones
■
■
■
PDAs
Laptops
EMI Graph 20in of Speaker Cable
300374a0
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation
300374
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Typical Application
30037459
FIGURE 1. Typical Audio Amplifier Application Circuit
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Connection Diagram
LLP Package
3mm x 3mm x 0.8mm
30037458
Top View
Order Number LM48310SD
See NS Package Number SDA010
Pin Descriptions
TABLE 1.
Pin
1
Name
IN+
Description
Non-Inverting Input
2
IN-
Inverting Input
Power Supply
3
VDD
SD
4
Active Low Shutdown Input. Connect to VDD for normal operation.
Mode Select and External Oscillator Input.
SYNC_IN = VDD: Spread spectrum mode with fS = 300kHz ± 30%
SYNC_IN = GND: Fixed frequency mode with fS = 300kHz
SYNC_IN = Clocked: fS = external clock frequency
5
SYNC_IN
6
7
SYNC_OUT Clock Output
OUTB
GND
Inverting Output
Ground
8
9
PVDD
OUTA
H-Bridge Power Supply
Non-Inverting Output
10
3
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Junction Temperature
Thermal Resistance
ꢁθJC
150°C
Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
49.2°C/W
8.2°C/W
ꢁθJA
Supply Voltage
Storage Temperature
Input Voltage
6.0V
−65°C to +150°C
− 0.3V to VDD +0.3V
Internally Limited
2000V
Operating Ratings (Notes 1, 2)
Temperature Range
Power Dissipation (Note 3)
ESD Rating (Note 4)
ESD Rating (Note 5)
TMIN ≤ TA ≤ TMAX
Supply Voltage
−40°C ≤ TA ≤ +85°C
2.4V ≤ VDD ≤ 5.5V
200V
Electrical Characteristics VDD = PVDD = 5V (Notes 2, 8)
The following specifications apply for AV = 12dB, (RL = 8Ω, SYNC_IN = VDD (Spread Spectrum mode), f = 1kHz, unless otherwise
specified. Limits apply for TA = 25°C.
LM48310
Units
Symbol
VOS
Parameter
Conditions
Typical
(Note 6)
1
Limit
(Notes 7, 8)
3
(Limits)
mV (max)
mA (max)
VIN = 0
Differential Output Offset Voltage
VIN = 0, RL = ∞
2.7
3.2
3.9
4.4
VDD = 3.6V
IDD
Quiescent Power Supply Current
Quiescent Power Supply Current
VIN = 0, RL = ∞
mA (max)
VDD = 5V
VIN = 0, VDD = 3.6V
VIN = 0, VDD = 5V
VSD = GND
2.7
3.2
mA
mA
IDD
ISD
Shutdown Current
0.01
1.0
1.4
0.4
μA
VIH
VIL
SD input, VDD = 3.6V
SD input, VDD = 3.6V
Logic Input High Voltage
Logic Input Low Voltage
Wake Up Time
V (min)
V (max)
ms
TWU
7.5
300±30
300
SYNC_IN = VDD (Spread Spectrum)
SYNC_IN = GND (Fixed Frequency)
kHz
kHz
SYNC_IN = External Clock
Minimum Frequency
fSW
Switching Frequency
200
kHz
kHz
SYNC_IN = External Clock
Maximum Frequency
1000
11
13
dB (min)
dB (max)
AV
Gain
12
20
RIN
Input Resistance
17
kΩ (min)
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LM48310
Typical
Units
(Limits)
Symbol
Parameter
Conditions
Limit
(Note 6)
(Notes 7, 8)
RL = 4Ω, THD = 10%
f = 1kHz, 22kHz BW
VDD = 5V
2.6
1.3
W
W
VDD = 3.6V
VDD = 2.5V
555
mW
RL = 8Ω, THD = 10% (max)
f = 1kHz, 22kHz BW
VDD = 5V
1.6
800
354
W
mW
mW
VDD = 3.6V
VDD = 2.5V
PO
Output Power
RL = 4Ω, THD = 1% (max)
f = 1kHz, 22kHz BW
VDD = 5V
2.1
1
W
W
VDD = 3.6V
VDD = 2.5V
446
mW
RL = 8Ω, THD = 1% (max)
f = 1kHz, 22kHz BW
VDD = 5V
1.1
1.3
640
286
W (min)
mW
mW
VDD = 3.6V
VDD = 2.5V
PO = 200mW, RL = 8Ω, f = 1kHz
PO = 100mW, RL = 8Ω, f = 1kHz
0.03
0.03
% (max)
%
THD+N
PSRR
Total Harmonic Distortion + Noise
VRIPPLE = 200mVP-P Sine,
fRIPPLE = 217Hz, Inputs AC GND,
CIN = 1μF, Input referred
82
80
dB
dB
Power Supply Rejection Ratio
(Input Referred)
VRIPPLE = 200mVP-P Sine,
fRIPPLE = 1kHz, Inputs AC GND,
CIN = 1μF, Input referred
VRIPPLE = 1VP-P
fRIPPLE = 217Hz
CMRR
Common Mode Rejection Ratio
Efficiency
70
88
dB
%
VDD = 5V, POUT = 1W
RL = 8Ω, f = 1kHz
η
VDD = 3.6V, POUT = 400mW
RL = 8Ω, f = 1kHz
85
97
97
%
VDD = 5V, PO = 1W,
Fixed Frequency Mode
VDD = 5V, PO = 1W,
Spread Spectrum Mode
dB
dB
SNR
Signal to Noise Ratio
Output Noise
Input referred,
Fixed Frequency Mode,
A-weighted Filter
14
28
μV
μV
εOS
Input referred,
Spread Spectrum Mode,
Unweighted
5
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Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability
and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in
the Recommended Operating Conditions is not implied. The Recommended Operating Conditionsindicate conditions at which the device is functional and the
device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified
or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.
Note 3: 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.
Note 4: Human body model, applicable std. JESD22-A114C.
Note 5: Machine model, applicable std. JESD22-A115-A.
Note 6: Typical values represent most likely parametric norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product
characterization and are not guaranteed.
Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis.
Note 8: RL is a resistive load in series with two inductors to simulate an actual speaker load. For RL = 8Ω, the load is 15µH + 8Ω, +15µH. For RL = 4Ω, the load
is 15µH + 4Ω + 15µH.
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Typical Performance Characteristics
THD+N vs Frequency
VDD = 2.5V, POUT = 300mW, RL = 4Ω
THD+N vs Frequency
VDD = 3.6V, POUT = 700mW, RL = 4Ω
30037466
30037467
THD+N vs Frequency
VDD = 5.0V, POUT = 1.2W, RL = 4Ω
THD+N vs Frequency
VDD = 2.5V, POUT = 150mW, RL = 8Ω
30037468
30037469
THD+N vs Frequency
VDD = 3.6V, POUT = 400mW, RL = 8Ω
THD+N vs Frequency
VDD = 5V, POUT = 650mW, RL = 8Ω
30037470
30037471
7
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THD+N vs Output Power
THD+N vs Output Power
f = 1kHz, RL = 4Ω
f = 1kHz, RL = 8Ω
30037464
30037465
Efficiency vs Output Power
Efficiency vs Output Power
f = 1kHz, RL = 4Ω
f = 1kHz, RL = 8Ω
30037473
30037472
Power Dissipation vs Output Power
Power Dissipation vs Output Power
f = 1kHz, RL = 4Ω
f = 1kHz, RL = 8Ω
30037475
30037474
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Output Power vs Supply Voltage
Output Power vs Supply Voltage
f = 1kHz, RL = 4Ω
f = 1kHz, RL = 8Ω
30037476
30037477
PSRR vs Frequency
VDD = 3.6V, VRIPPLE = 200mVP-P, RL = 8Ω
PSRR vs Frequency
VDD = 5.0V, VRIPPLE = 200mVP-P, RL = 8Ω
30037498
30037497
CMRR vs Frequency
VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω
CMRR vs Frequency
VDD = 5.0V, VRIPPLE = 1VP-P, RL = 8Ω
30037463
30037480
9
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Fixed Frequency Output Spectrum vs Frequency
Spread Spectrum Output Spectrum vs Frequency
VDD = 5.0V, VIN = 1VRMS, RL = 8Ω
VDD = 5.0V, VIN = 1VRMS, RL = 8Ω
30037482
30037483
Wideband Fixed Frequency Output Spectrum
vs Frequency
Wideband Spread Spectrum Output Spectrum
vs Frequency
VDD = 5.0V, RL = 8Ω
VDD = 5.0V, RL = 8Ω
30037484
30037485
Supply Current vs Supply Voltage
No Load
Shutdown Supply Current vs Supply Voltage
No Load
30037499
30037486
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Application Information
GENERAL AMPLIFIER FUNCTION
spectrum mode, the switching frequency varies randomly by
30% about a 300kHz center frequency, reducing the wide-
band 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 LM48310 spreads that energy over a larger
bandwidth (See Typical Performance Characteristics). The
cycle-to-cycle variation of the switching period does not affect
the audio reproduction, efficiency, or PSRR. Set SYNC_IN =
VDD for spread spectrum mode.
The LM48310 mono Class D audio power amplifier features
a filterless modulation scheme that reduces external compo-
nent count, conserving board space and reducing system
cost. With no signal applied, the outputs (VOUTA and VOUTB
)
switch between VDD and GND with a 50% duty cycle, in
phase, causing the two outputs to cancel. This cancellation
results in no net voltage across the speaker, thus there is no
current to the load in the idle state.
With the input signal applied, the duty cycle (pulse width) of
the LM48310 outputs changes. For increasing output voltage,
the duty cycle of VOUTAincreases, while the duty cycle of
VOUTB decreases. For decreasing output voltages, the con-
verse occurs. The difference between the two pulse widths
yields the differential output voltage.
EXTERNAL CLOCK MODE (SYNC_IN = CLOCK)
Connecting a clock signal to SYNC_IN synchronizes the
LM48310 oscillator to an external clock, moving the output
spectral components out of a sensitive frequency band, and
minimizing audible beat frequencies when multiple LM48310s
are used in a single system. The LM48310 accepts an exter-
nal clock frequency between 200kHz and 1MHz. The
LM48310 can be synchronized to a spread spectrum clock,
allowing multiple LM48310s to be synchronized in spread
spectrum mode (see SYNC_OUT section).
ENHANCED EMISSIONS SUPPRESSION SYSTEM (E2S)
The LM48310 features National’s patent-pending E2S system
that reduces EMI, while maintaining high quality audio repro-
duction and efficiency. The E2S system features a synchro-
nizable oscillator with selectable spread spectrum, and
advanced edge rate control (ERC). The LM48310 ERC great-
ly reduces the high frequency components of the output
square waves by controlling the output rise and fall times,
slowing the transitions to reduce RF emissions, while maxi-
mizing THD+N and efficiency performance. The overall result
of the E2S system is a filterless Class D amplifier that passes
FCC Class B radiated emissions standards with 20in of twist-
ed pair cable, with excellent 0.03% THD+N and high 88%
efficiency.
SYNC_OUT
SYNC_OUT is a clock output for synchronizing external de-
vices. The SYNC_OUT signal is identical in frequency and
duty cycle of the amplifier’s switching frequency. When the
LM48310 is in fixed frequency mode, SYNC_OUT is a fixed,
300kHz clock. When the LM48310 is in spread spectrum
mode, SYNC_OUT is an identical spread spectrum clock.
When the LM48310 is driven by an external clock,
SYNC_OUT is identical to the external clock. If unused, leave
SYNC_OUT floating.
FIXED FREQUENCY MODE (SYNC_IN = GND)
The LM48310 features two modulations schemes, a fixed fre-
quency mode and a spread spectrum mode. Select the fixed
frequency mode by setting SYNC_IN = GND. In fixed fre-
quency mode, the amplifier output switch at a constant
300kHz. In fixed frequency mode, the output spectrum con-
sists of the fundamental and its associated harmonics (see
Typical Performance Characteristics).
Multiple LM48310s can be synchronized to a single clock. In
Figure 2, device U1 is the master, providing a spread spec-
trum clock to the slave device (U2). This configuration syn-
chronizes the switching frequencies of the two devices,
eliminating any audible beat frequencies. Because
SYNC_OUT has no audio content, there is minimal THD+N
degredation or crosstalk between the devices, Figure 3-5.
SPREAD SPECTRUM MODE (SYNC_IN = VDD
)
The logic selectable spread spectrum mode eliminates the
need for output filters, ferrite beads or chokes. In spread
11
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30037460
FIGURE 2. Cascaded LM48310
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30037438
FIGURE 3. THD+N vs Output Powe3r00374a1
FIGURE 4. THD+N vs Frequency
FIGURE 5. Crosstalk vs Frequency30037496
13
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DIFFERENTIAL AMPLIFIER EXPLANATION
Where RIN is the value of the input resistor given in the Elec-
trical Characteristics table.
As logic supplies continue to shrink, system designers are in-
creasingly turning to differential analog signal handling to
preserve signal to noise ratios with restricted voltage signs.
The LM48310 features a fully differential speaker amplifier. A
differential amplifier amplifies the difference between the two
input signals. Traditional audio power amplifiers have typical-
ly offered only single-ended inputs resulting in a 6dB reduc-
tion of SNR relative to differential inputs. The LM48310 also
offers the possibility of DC input coupling which eliminates the
input coupling capacitors. A major benefit of the fully differ-
ential amplifier is the improved common mode rejection ratio
(CMRR) over single ended input amplifiers. The increased
CMRR of the differential amplifier reduces sensitivity to
ground offset related noise injection, especially important in
noisy systems.
The input capacitors can also be used to remove low fre-
quency content from the audio signal. Small speakers cannot
reproduce, and may even be damaged by low frequencies.
High pass filtering the audio signal helps protect the speakers.
When the LM48310 is using a single-ended source, power
supply noise on the ground is seen as an input signal. Setting
the high-pass filter point above the power supply noise fre-
quencies, 217Hz in a GSM phone, for example, filters out the
noise such that it is not amplified and heard on the output.
Capacitors with a tolerance of 10% or better are recommend-
ed for impedance matching and improved CMRR and PSRR.
AUDIO AMPLIFIER GAIN
The gain of the LM48310 is internally set to 12dB. The gain
can be reduced by adding additional input resistance (Figure
6). In this configuration, the gain of the device is given by:
POWER DISSIPATION AND EFFICIENCY
The major benefit of a Class D amplifier is increased efficiency
versus a Class AB. The efficiency of the LM48310 is attributed
to the region of operation of the transistors in the output stage.
The Class D output stage acts as current steering switches,
consuming negligible amounts of power compared to their
Class AB counterparts. Most of the power loss associated
with the output stage is due to the IR loss of the MOSFET on-
resistance, along with switching losses due to gate charge.
AV = 2 x [RF / (RINEXT + RIN)]
Where RF is 40kΩ, RIN is 20kΩ, and RINEXT is the value of the
additional external resistor.
SHUTDOWN FUNCTION
The LM48310 features a low current shutdown mode. Set
SD = GND to disable the amplifier and reduce supply current
to 0.01µA.
Switch SD between GND and VDD for minimum current con-
sumption is shutdown. The LM48310 may be disabled with
shutdown voltages in between GND and VDD, the idle current
will be greater than the typical 0.1µA value.
The LM48310 shutdown input has and internal pulldown re-
sistor. The purpose of this resistor is to eliminate any unwant-
ed state changes when SD is floating. To minimize shutdown
current, SD should be driven to GND or left floating. If SD is
not driven to GND or floating, an increase in shutdown supply
current will be noticed.
30037461
FIGURE 6. Reduced Gain Configuration
SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION
AUDIO AMPLIFIER POWER SUPPLY BYPASSING/
FILTERING
The LM48310 is compatible with single-ended sources. When
configured for single-ended inputs, input capacitors must be
used to block and DC component at the input of the device.
Figure 7 shows the typical single-ended applications circuit.
Proper power supply bypassing is critical for low noise per-
formance and high PSRR. Place the supply bypass capaci-
tors as close to the device as possible. Typical applications
employ a voltage regulator with 10µF and 0.1µF bypass ca-
pacitors that increase supply stability. These capacitors do
not eliminate the need for bypassing of the LM48310 supply
pins. A 1µF capacitor is recommended.
AUDIO AMPLIFIER INPUT CAPACITOR SELECTION
Input capacitors may be required for some applications, or
when the audio source is single-ended. Input capacitors block
the DC component of the audio signal, eliminating any conflict
between the DC component of the audio source and the bias
voltage of the LM48310. The input capacitors create a high-
pass filter with the input resistors RIN. The -3dB point of the
high pass filter is found using Equation (1) below.
f = 1 / 2πRINCIN
30037462
FIGURE 7. Single-Ended Input Configuration
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PCB LAYOUT GUIDELINES
As output power increases, interconnect resistance (PCB
traces and wires) between the amplifier, load and power sup-
ply create a voltage drop. The voltage loss due to the traces
between the LM48310 and the load results in lower output
power and decreased efficiency. Higher trace resistance be-
tween the supply and the LM48310 has the same effect as a
poorly regulated supply, increasing ripple on the supply line,
and reducing peak output power. The effects of residual trace
resistance increases as output current increases due to high-
er output power, decreased load impedance or both. To main-
tain 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.
As the distance from the LM48310 and the speaker increases,
the amount of EMI radiation increases due to the output wires
or traces acting as antennas become more efficient with
length. Ferrite chip inductors places close to the LM48310
outputs may be needed to reduce EMI radiation.
Designator Quantity
Description
C1
1
2
2
1
10μF ±10% 16V 500Ω Tantalum
Capacitor (B Case) AVX
TPSB106K016R0500
C2, C3
C4, C5
C6
1μF ±10% 16V X7R Ceramic
Capacitor (603) Panasonic
ECJ-1VB1C105K
The use of power and ground planes will give the best THD
+N performance. In addition to reducing trace resistance, the
use of power planes creates parasitic capacitors that help to
filter the power supply line.
1μF ±10% 16V X7R Ceramic
Capacitor (1206) Panasonic
ECJ-3YB1C105K
Not Installed Ceramic Capacitor
(603)
The inductive nature of the transducer load can also result in
overshoot on one of both edges, clamped by the parasitic
diodes to GND and VDD in each case. From an EMI stand-
point, this is an aggressive waveform that can radiate or
conduct to other components in the system and cause inter-
ference. In is essential to keep the power and output traces
short and well shielded if possible. Use of ground planes
beads and micros-strip layout techniques are all useful in pre-
venting unwanted interference.
R1
1
2
1
0Ω ±1% resistor (603)
3 Pin Headers
JP1 — JP2
LM48310SDL
LM48310SD (10-pin LLP)
15
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LM48310 Demo Board Schematic
30037489
FIGURE 8. LM48310 DEMO BOARD SCHEMATIC
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16
Demo Boards
30037491
30037490
FIGURE 10. Top Layer
FIGURE 9. Top Silkscreen
30037493
30037492
FIGURE 12. Layer 3 (VDD
)
FIGURE 11. Layer 2 (GND)
30037494
30037495
FIGURE 13. Bottom Layer
FIGURE 14. Bottom Silkscreen
17
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Revision History
Rev
1.0
Date
Description
11/13/07
02/26/08
03/04/08
Initial release.
1.01
1.02
Fixed few typos (Pin Description table).
Text edits under SHUTDOWN FUNCTION (Application Information
section).
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18
Physical Dimensions inches (millimeters) unless otherwise noted
LLP
Order Number LM48310SD
NS Package Number SDA08A
19
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