LM4953
Ground-Referenced, Ultra Low Noise, Ceramic Speaker
Driver
General Description
The LM4953 is an audio power amplifier designed for driving
Ceramic Speaker in portable applications. When powered by
a 3.6V supply, it is capable of forcing 12.6Vpp across a 2µF
+30Ωbridge-tied-load (BTL) with less than 1% THD+N.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4953 does not require boot-
strap capacitors, or snubber circuits. Therefore it is ideally
suited for display applications requiring high power and mini-
mal size.
The LM4953 features a low-power consumption shutdown
mode. Additionally, the LM4953 features an internal thermal
shutdown protection mechanism.
The LM4953 contains advanced pop & click circuitry that
eliminates noises which would otherwise occur during
turn-on and turn-off transitions.
The LM4953 is unity-gain stable and can be configured by
external gain-setting resistors.
Key Specifications
jQuiescent Power Supply Current (V
dd
= 3V) 7mA(typ)
jBTL Voltage Swing
(2µF+30Ωload, 1% THD+N, V
dd
= 3.6V) 12.6V
pp
(typ)
jShutdown Current 1µA (max)
Features
nPop & click circuitry eliminates noise during turn-on and
turn-off transitions
nLow, 1µA (max) shutdown current
nLow, 7mA (typ) quiescent current
n12.6Vpp mono BTL output, load = 2µF+ 30Ω
nThermal shutdown
nUnity-gain stable
nExternal gain configuration capability
Applications
nCellphone
nPDA
Typical Application
Boomer®is a registered trademark of National Semiconductor Corporation.
20142168
FIGURE 1. Typical Application Circuit
February 2006
LM4953 Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver
© 2006 National Semiconductor Corporation DS201421 www.national.com
Connection Diagram
LLP Package
20142101
Top View
Order Number LM4953SD
See NS Package Number SDA14A
Pin Descriptions
Pin Name Function
1 SD Active Low Shutdown
2CP
VDD
Charge Pump Power Supply
3 CCP+ Positive Terminal - Charge Pump Flying Capacitor
4 PGND Power Ground
5 CCP- Negative Terminal - Charge Pump Flying Capacitor
6V
CP_OUT
Charge Pump Output
7 NC No Connect
8AV
SS
Negative Power Supply - Amplifier
9 OUT B Output B
10 AV
DD
Positive Power Supply - Amplifier
11 OUT A Output A
12 NC No Connect
13 V
IN
Signal Input
14 SGND Signal Ground
LM4953
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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.
Supply Voltage (V
DD
) 4.5V
Storage Temperature −65˚C to +150˚C
Input Voltage -0.3V to V
DD
+ 0.3V
Power Dissipation (Note 3) Internally Limited
ESD Susceptibility (Note 4) 2000V
ESD Susceptibility (Note 5) 200V
Junction Temperature 150˚C
Thermal Resistance
See AN-1187 ’Leadless Leadframe Packaging (LLP).’
Operating Ratings
Temperature Range
T
MIN
≤T
A
≤T
MAX
−40˚C ≤T
A
≤85˚C
Supply Voltage (V
DD
) 1.6V ≤V
DD
≤4.2V
Electrical Characteristics V
DD
= 3.6V
The following specifications apply for V
DD
= 3.6V, A
V-BTL
= 6dB, Z
L
= 2µF+30Ωunless otherwise specified. Limits apply to T
A
=
25˚C. See Figure 1.
Symbol Parameter Conditions LM4953 Units (Limits)
Typ
(Note 6)
Limit
(Notes 7, 8)
I
DD
Quiescent Power Supply
Current V
IN
=0,R
LOAD
= 2µF+30Ω8 mA (max)
I
standby
Quiescent Power Supply
Current Auto Standby Mode V
IN
=0,Z
LOAD
= 2µF+30Ω2.7 mA
I
SD
Shutdown Current V
SD
= GND 0.1 1 µA (max)
V
SDIH
Shutdown Voltage Input High SD1
SD2 0.7*CPVdd V (min)
V
SDIL
Shutdown Voltage Input Low SD1
SD2 0.3*CPVdd V (max)
T
WU
Wake-up Time 125 µsec
V
OS
Output Offset Voltage 1 10 mV (max)
V
OUT
Output Voltage Swing THD = 1% (max); f = 1kHz
R
L
= 2µF+30Ω, Mono BTL 12.6 Vpp
THD+N Total Harmonic Distortion +
Noise V
OUT
= 6Vp-p, f
IN
= 1kHz 0.02 %
∈
OS
Output Noise A-Weighted Filter, V
IN
=0V 15 µV
PSRR Power Supply Rejection
Ratio
V
RIPPLE
= 200mVp-p, f = 217Hz,
Input Referred 67 dB
V
RIPPLE
= 200mVp-p, f = 1kHz,
Input Referred 65 dB
SNR Signal-to-Noise Ratio Z
L
= 2µF+30Ω,V
OUT
= 6Vp-p 105 dB
Electrical Characteristics V
DD
= 3.0V
The following specifications apply for V
DD
= 3.0V, A
V-BTL
= 6dB, Z
L
= 2µF+30Ωunless otherwise specified. Limits apply to T
A
=
25˚C. See Figure 1.
Symbol Parameter Conditions LM4953 Units (Limits)
Typ
(Note 6)
Limit
(Notes 7, 8)
I
DD
Quiescent Power Supply
Current V
IN
=0,Z
LOAD
= 2µF+30Ω7 10 mA (max)
I
standby
Quiescent Power Supply
Current Auto Standby Mode V
IN
=0,Z
LOAD
= 2µF+30Ω2.3 mA
I
SD
Shutdown Current V
SD-LC
=V
SD-RC
= GND 0.1 1 µA (max)
V
SDIH
Shutdown Voltage Input High SD1
SD2 0.7*CPVdd V (min)
LM4953
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Electrical Characteristics V
DD
= 3.0V (Continued)
The following specifications apply for V
DD
= 3.0V, A
V-BTL
= 6dB, Z
L
= 2µF+30Ωunless otherwise specified. Limits apply to T
A
=
25˚C. See Figure 1.
Symbol Parameter Conditions LM4953 Units (Limits)
Typ
(Note 6)
Limit
(Notes 7, 8)
V
SDIL
Shutdown Voltage Input Low SD1
SD2 0.3*CPVdd V (max)
T
WU
Wake-up Time 125 µsec
V
OS
Output Offset Voltage 1 10 mV (max)
V
OUT
Output Voltage Swing THD = 1% (max); f = 1kHz
Z
L
= 2µF+30Ω, Mono BTL 10.2 Vpp
THD+N Total Harmonic Distortion +
Noise V
OUT
= 8.5Vp-p, f
IN
= 1kHz 0.02 %
∈
OS
Output Noise A-Weighted Filter, V
IN
=0V 15 µV
PSRR Power Supply Rejection
Ratio
V
RIPPLE
= 200mVp-p, f = 217Hz,
Input Referred 73 dB
V
RIPPLE
= 200mVp-p, f = 1kHz,
Input Referred 68 dB
SNR Signal-to-Noise Ratio Z
L
= 2µF+30Ω,V
OUT
= 8.5Vp-p 105 dB
Note 1: All voltages are measured with respect to the GND pin unless otherwise specified.
Note 2: 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 guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions that
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given; however, the typical value is a good indication of device performance.
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 =(T
JMAX –T
A)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4xxx typical application
(shown in Figure 1) with VDD = yyV, RL= 2µF+30Ωmono BTL operation the total power dissipation is xxxW. θJA = 40˚C/W.
Note 4: Human body model, 100pF discharged through a 1.5kΩresistor.
Note 5: Machine Model, 220pF-240pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 9: If the product is in shutdown mode and VDD exceeds 3.6V (to a max of 4V VDD), then most of the excess current will flow through the ESD protection circuits.
If the source impedance limits the current to a max of 10mA, then the part will be protected. If the part is enabled when VDD is above 4V, circuit performance will
be curtailed or the part may be permanently damaged.
LM4953
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Typical Performance Characteristics
THD+N vs Frequency
V
DD
= 2V, V
O
= 2Vpp, Z
L
= 2µF+30Ω
THD+N vs Frequency
V
DD
= 3V, V
O
= 6Vpp, Z
L
= 2µF+30Ω
20142112 20142113
THD+N vs Frequency
V
DD
= 3.6V, V
O
= 8.5Vpp, Z
L
= 2µF+30Ω
THD+N vs Frequency
V
DD
= 4.2V, V
O
= 10Vpp, Z
L
= 2µF+30Ω
20142114 20142118
THD+N vs Output Voltage
V
DD
= 2V, f = 1kHz, Z
L
= 2µF+30Ω
THD+N vs Output Voltage
V
DD
= 3V, f = 1kHz, Z
L
= 2µF+30Ω
20142119 20142121
LM4953
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Typical Performance Characteristics (Continued)
THD+N vs Output Voltage
V
DD
= 3.6V, f = 1kHz, Z
L
= 2µF+30Ω
THD+N vs Output Voltage
V
DD
= 4.2V, f = 1kHz, Z
L
= 2µF+30Ω
20142120 20142122
PSRR vs Frequency
V
DD
= 2V, Z
L
= 2µF+30Ω
PSRR vs Frequency
V
DD
= 3V, Z
L
= 2µF+30Ω
20142123 20142125
PSRR vs Frequency
V
DD
= 3.6V, Z
L
= 2µF+30Ω
PSRR vs Frequency
V
DD
= 4.2V, Z
L
= 2µF+30Ω
20142124 20142126
LM4953
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Typical Performance Characteristics (Continued)
Supply Current vs Supply Voltage
Z
L
= 2µF+30Ω
20142127
LM4953
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Application Information
ELIMINATING THE OUTPUT COUPLING CAPACITOR
The LM4953 features a low noise inverting charge pump that
generates an internal negative supply voltage. This allows
the outputs of the LM4953 to be biased about GND instead
of a nominal DC voltage, like traditional headphone amplifi-
ers. Because there is no DC component, the large DC
blocking capacitors (typically 220µF) are not necessary. The
coupling capacitors are replaced by two, small ceramic
charge pump capacitors, saving board space and cost.
Eliminating the output coupling capacitors also improves low
frequency response. In traditional headphone amplifiers, the
headphone impedance and the output capacitor form a high
pass filter that not only blocks the DC component of the
output, but also attenuates low frequencies, impacting the
bass response. Because the LM4953 does not require the
output coupling capacitors, the low frequency response of
the device is not degraded by external components.
In addition to eliminating the output coupling capacitors, the
ground referenced output nearly doubles the available dy-
namic range of the LM4953 when compared to a traditional
headphone amplifier operating from the same supply volt-
age.
BRIDGE CONFIGURATION EXPLANATION
The Audio Amplifier portion of the LM4953has two internal
amplifiers allowing different amplifier configurations. The first
amplifier’s gain is externally configurable, whereas the sec-
ond amplifier is internally fixed in a unity-gain, inverting
configuration. The closed-loop gain of the first amplifier is set
by selecting the ratio of Rf to Ri while the second amplifier’s
gain is fixed by the two internal 20kΩresistors. Figure 1
shows that the output of amplifier one serves as the input to
amplifier two. This results in both amplifiers producing sig-
nals identical in magnitude, but out of phase by 180˚. Con-
sequently, the differential gain for the Audio Amplifier is
A
VD
= 2 *(Rf/Ri)
By driving the load differentially through outputs OUT A and
OUT B, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classic single-ended amplifier configura-
tion where one side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration. It provides differential drive
to the load, thus doubling the output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same con-
ditions. This increase in attainable output power assumes
that the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the Audio Power Amplifier
Design section.
The bridge configuration also creates a second advantage
over single-ended amplifiers. Since the differential outputs,
OUT A and OUT B, are biased at half-supply, no net DC
voltage exists across the load. This eliminates the need for
an output coupling capacitor which is required in a single
supply, single-ended amplifier configuration. Without an out-
put coupling capacitor, the half-supply bias across the load
would result in both increased internal IC power dissipation
and also possible loudspeaker damage.
OUTPUT TRANSIENT (’CLICK AND POPS’)
ELIMINATED
The LM4953 contains advanced circuitry that virtually elimi-
nates output transients (’clicks and pops’). This circuitry
prevents all traces of transients when the supply voltage is
first applied or when the part resumes operation after coming
out of shutdown mode.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation 1 states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.
P
DMAX
=(V
DD
)
2
/(2π
2
Z
L
) (1)
Since the LM4953 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. Even
with large internal power dissipation, the LM4953 does not
require heat sinking over a large range of ambient tempera-
tures. The maximum power dissipation point obtained must
not be greater than the power dissipation that results from
Equation 2:
P
DMAX
=(T
JMAX
-T
A
)/(θ
JA
) (2)
Depending on the ambient temperature, T
A
, of the system
surroundings, Equation 2 can be used to find the maximum
internal power dissipation supported by the IC packaging. If
the result of Equation 1 is greater than that of Equation 2,
then either the supply voltage must be decreased, the load
impedance increased or T
A
reduced. Power dissipation is a
function of output power and thus, if typical operation is not
around the maximum power dissipation point, the ambient
temperature may be increased accordingly.
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 3V power supply typi-
cally use a 4.7µF capacitor in parallel with a 0.1µF ceramic
filter capacitor to stabilize the power supply’s output, reduce
noise on the supply line, and improve the supply’s transient
response. Keep the length of leads and traces that connect
capacitors between the LM4953’s power supply pin and
ground as short as possible.
AUTOMATIC STANDBY MODE
The LM4953 features Automatic Standby Mode circuitry
(patent pending). In the absence of an input signal, after
approximately 3 seconds, the LM4953 goes into low current
standby mode. The LM4953 recovers into full power operat-
ing mode immediately after a signal, which is greater than
the input threshold voltage, is applied to either the left or right
input pins. The input threshold voltage is not a static value,
as the supply voltage increases, the input threshold voltage
decreases. This feature reduces power supply current con-
sumption in battery operated applications.
To ensure correct operation of Automatic Standby Mode,
proper layout techniques should be implemented. Separat-
ing PGND and SGND can help reduce noise entering the
LM4953 in noisy environments. It is also important to use
LM4953
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Application Information (Continued)
correct power off sequencing. The device should be in shut-
down and then powered off in order to ensure proper func-
tionality of the Auto-Standby feature. While Automatic
Standby Mode reduces power consumption very effectively
during silent periods, maximum power saving is achieved by
putting the device into shutdown when it is not in use.
MICRO POWER SHUTDOWN
The voltage applied to the SD controls the LM4953’s shut-
down function. When active, the LM4953’s micropower shut-
down feature turns off the amplifiers’ bias circuitry, reducing
the supply current. The trigger point is 0.3*CPV
DD
for a
logic-low level, and 0.7*CPV
DD
for logic-high level. The low
0.01µA (typ) shutdown current is achieved by applying a
voltage that is as near as ground a possible to the SD pins.
A voltage that is higher than ground may increase the shut-
down current.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 100kΩpull-up resistor between the SD
pins and V
DD
. Connect the switch between the SD pins and
ground. Select normal amplifier operation by opening the
switch. Closing the switch connects the SD pins to ground,
activating micro-power shutdown. The switch and resistor
guarantee that the SD pins will not float. This prevents
unwanted state changes. In a system with a microprocessor
or microcontroller, use a digital output to apply the control
voltage to the SD pins. Driving the SD pins with active
circuitry eliminates the pull-up resistor.
EXPOSED-DAP CONSIDERATIONS
It is essential that the exposed Die Attach Paddle (DAP), for
the LM4953, is NOT connected to GND. For optimal opera-
tion it should be connected to AVss and VCP-OUT (Pins 6
and 8).
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4953’s performance requires properly se-
lecting external components. Though the LM4953 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
Charge Pump Capacitor Selection
Use low ESR (equivalent series resistance) (<100mΩ) ce-
ramic capacitors with an X7R dielectric for best perfor-
mance. Low ESR capacitors keep the charge pump output
impedance to a minimum, extending the headroom on the
negative supply. Higher ESR capacitors result in reduced
output power from the audio amplifiers.
Charge pump load regulation and output impedance are
affected by the value of the flying capacitor (C1). A larger
valued C1 (up to 3.3uF) improves load regulation and mini-
mizes charge pump output resistance. Beyond 3.3uF, the
switch-on resistance dominates the output impedance for
capacitor values above 2.2uF.
The output ripple is affected by the value and ESR of the
output capacitor (C2). Larger capacitors reduce output ripple
on the negative power supply. Lower ESR capacitors mini-
mize the output ripple and reduce the output impedance of
the charge pump.
The LM4953 charge pump design is optimized for 2.2uF, low
ESR, ceramic, flying, and output capacitors.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitors (C
i
in Figure 1). A high value ca-
pacitor can be expensive and may compromise space effi-
ciency in portable designs. In many cases, however, the
speakers used in portable systems, whether internal or ex-
ternal, have little ability to reproduce signals below 150Hz.
Applications using speakers with this limited frequency re-
sponse reap little improvement by using high value input and
output capacitors.
Besides affecting system cost and size, C
i
has an effect on
the LM4953’s click and pop performance. The magnitude of
the pop is directly proportional to the input capacitor’s size.
Thus, pops can be minimized by selecting an input capacitor
value that is no higher than necessary to meet the desired
−3dB frequency.
As shown in Figure 1, the internal input resistor, R
i
and the
input capacitor, C
i
, produce a -3dB high pass filter cutoff
frequency that is found using Equation (3). Conventional
headphone amplifiers require output capacitors; Equation (3)
can be used, along with the value of R
L
, to determine to-
wards the value of output capacitor needed to produce a
–3dB high pass filter cutoff frequency.
f
i-3dB
=1/2πR
i
C
i
(3)
Also, careful consideration must be taken in selecting a
certain type of capacitor to be used in the system. Different
types of capacitors (tantalum, electrolytic, ceramic) have
unique performance characteristics and may affect overall
system performance. (See the section entitled Charge Pump
Capacitor Selection.)
LM4953
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Application Information (Continued)
LM4953 DEMO BOARD ARTWORK
Top Layer Mid Layer 1
20142194 20142195
Mid Layer 2 Bottom Layer
20142196 20142197
LM4953
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Revision History
Rev Date Description
1.0 2/18/05 Started D/S by copying LM4926
(DS201161).
1.2 9/13/05 Added the Typ Perf curves and
Application Info section.
1.3 9/14/05 Added more Typ Perf curves.
First WEB release on the D/S.
1.4 9/19/05 Fixed some typo, then re-released D/S to
the WEB.
1.5 11/11/05 Added the LLP boards, then re-released
D/S to the WEB... not released on this
date..
1.6 11/14/05 Added the LLP boards, then re-released
D/S to the WEB (per Nisha).
1.7 11/15/05 Text edit.
1.8 12/21/05 Added the EXPOSED-DAP
CONSIDERATIONS (Application Info
section), then re-released D/S to the
WEB.
1.9 2/01/06 Edited 20142168 (Typ Appl ckt)..., then
re-released D/S to the WEB.
LM4953
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Physical Dimensions inches (millimeters) unless otherwise noted
LLP Package
Order Number LM4953SD
NS Package Number SDA14A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
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National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
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LM4953 Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver
