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PDF LM48556 Data sheet ( Hoja de datos )
| Número de pieza | LM48556 | |
| Descripción | Ceramic Speaker Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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December 10, 2008
LM48556
Fully Differential, Mono, Ceramic Speaker Driver
General Description
The LM48556 is a single supply, mono, ceramic speaker driv-
er with an integrated charge-pump, designed for portable
devices, such as cell phones, where board space is at a pre-
mium. The LM48556 charge pump allows the device to deliver
17.5VPP (typ) from a single 4.5V supply. Additionally, the
charge pump features a soft start function that minimizes
transient current during power-up.
The LM48556 features high power supply rejection ratio
(PSRR) of 80dB at 217Hz, allowing the device to operate in
noisy environments without additional power supply condi-
tioning. Flexible power supply requirements allow operation
from 2.7V to 5.0V. Additionally, the LM48556 features a dif-
ferential input function and an externally configurable gain. A
low power shutdown mode reduces supply current consump-
tion to 0.1μA.
Superior click and pop suppression eliminates audible tran-
sients on power-up/down and during shutdown. The
LM48556 is available in an ultra-small 12-bump micro SMD
package (2mm x 1.5mm).
Key Specifications
■ Output Voltage Swing
VDD = 3.6V, 1kHz
VDD = 4.5V, 1kHz
■ Power Supply Rejection Ratio
f = 217Hz, VDD = 3.6V
■ IDD at VDD = 3.6V
■ Wake-Up Time
Features
■ Fully differential amplifier
■ Externally configurable gain
■ Integrated charge pump
■ Low power shutdown mode
■ Soft start function
Applications
■ Mobile phones
■ PDA's
■ Digital cameras
14.2VPP (typ)
17.5VPP (typ)
80dB (typ)
4.8mA (typ)
0.5ms (typ)
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 300572
www.DataSheet.in
www.national.com
1 page  
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 (SVDD, PVDD)
(Note 1)
Storage Temperature
Input Voltage
Power Dissipation (Note 3)
ESD Rating(Note 4)
ESD Rating (Note 5)
5.25V
−65°C to +150°C
−0.3V to VDD + 0.3V
Internally limited
2000V
200V
Junction Temperature
150°C
Thermal Resistance
θJA (TL)
Soldering Information
114°C/W
See AN-1112 Micro SMD Wafer Level Chip Scale
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage (SVDD, PVDD)
−40°C ≤ TA ≤ +85°C
2.7V ≤ _VDD ≤ 5.0V
Electrical Characteristics VDD = 3.6V (Note 2)
The following specifications apply for VDD = 3.6V, AV-BTL = 20dB (R F = 200kΩ, RIN = 20kΩ), ZL = 15Ω+1μF, unless otherwise
specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM48556
Typical
Limit
(Note 6) (Note 7)
Units
(Limits)
IDD Quiescent Power Supply Current VIN = 0V
ISD Shutdown Current
VSD = GND (Note 8)
4.8 7 mA (max)
0.1 1 µA (max)
VOS
TWU
VOUT
THD+N
εOS
Output Offset Voltage
Wake-up Time
Output Voltage Swing
Total Harmonic Distortion + Noise
Output Noise
CIN = 0.47μF, AV = 1V/V (0dB)
THD+N = 1% (max); f = 1kHz
THD+N = 1% (max); f = 10kHz
VOUT = 11VPP, f = 1kHz
AV = 0dB
AV = 20dB
A-weighted filter, VIN = 0V
Input referred
0.6
0.5
14.2
11.5
0.005
0.03
8
4 mV (max)
ms
VPP
11 VPP (min)
%
%
μV
PSRR
CMRR
Power Supply Rejection Ratio
Common Mode Rejection Ratio
VRIPPLE = 200mVPP, f = 217Hz
Input Referred
80 60 dB (min)
70 60 dB (min)
VLH Logic High Threshold Voltage
VLL Logic Low Threshold Voltage
1.2 V (min)
0.45 V (max)
Electrical Characteristics VDD = 4.5V (Note 2)
The following specifications apply for VDD = 4.5V, AV-BTL = 20dB (R F = 200kΩ, RIN = 20kΩ), ZL = 15Ω+1μF, unless otherwise
specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM48556
Typical
(Note 6)
Limit
(Note 7)
Units
(Limits)
IDD Quiescent Power Supply Current VIN = 0V
ISD Shutdown Current
VSD = GND (Note 8)
6.5 10 mA (max)
0.1 1 µA (max)
VOS
TWU
VOUT
THD+N
εOS
Output Offset Voltage
Wake-up Time
Output Voltage Swing
Total Harmonic Distortion + Noise
Output Noise
CIN = 0.47μF, AV = 1V/V (0dB)
THD+N = 1% (max); f = 1kHz
THD+N = 1% (max); f = 10kHz
VOUT = 14VPP, f = 1kHz
AV = 0dB
AV = 20dB
A-weighted filter, VIN = 0V
Input referred
0.6
0.5
17.5
14.6
0.005
0.03
8
4 mV (max)
ms (max)
VPP
14 VPP (min)
%
%
μV
5 www.national.com
www.DataSheet.in
5 Page 
Application Information
GENERAL AMPLIFIER FUNCTION
The LM48556 is a fully differential ceramic speaker driver that
utilizes National’s inverting charge pump technology to deliv-
er the high drive voltages required by ceramic speakers,
without the need for noisy, board-space consuming inductive
based regulators. The low-noise, inverting charge pump cre-
ates a negative supply (CPVSS) from the positive supply
(PVDD). Because the amplifiers operate from these bipolar
supplies, the maximum output voltage swing for each ampli-
fier is doubled compared to a traditional single supply device.
Additionally, the LM48556 is configured as a bridge-tied load
(BTL) device, quadrupling the maximum theoretical output
voltage range when compared to a single supply, single-end-
ed output amplifier, see Bridged Configuration Explained sec-
tion. The charge pump and BTL configuration allow the
LM48556 to deliver over 17VP-P at 1kHz to a 1µF ceramic
speaker while operating from a single 4.5V supply .
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM48556 features a differential input stage, which offers
improved noise rejection compared to a single-ended input
amplifier. Because a differential input amplifier amplifies the
difference between the two input signals, any component
common to both signals is cancelled. An additional benefit of
the differential input structure is the possible elimination of the
DC input blocking capacitors. Since the DC component is
common to both inputs, and thus cancelled by the amplifier,
the LM48556 can be used without input coupling capacitors
when configured with a differential input signal.
BRIDGE CONFIGURATION EXPLAINED
The LM48556 is designed to drive a load differentially, a con-
figuration commonly referred to as a bridge-tied load (BTL).
The BTL configuration differs from the single-ended configu-
ration, where one side of the load is connected to ground. A
BTL amplifier offers advantages over a single-ended device.
Driving the load differentially doubles the output voltage com-
pared to a single-ended amplifier under similar conditions.
Any component common to both outputs is cancelled, thus
there is no net DC voltage across the load, eliminating the DC
blocking capacitors required by single-ended, single-supply
amplifiers.
SHUTDOWN FUNCTION
The LM48556 features a low current shutdown mode. Set
SD = GND to disable the amplifier and reduce supply current
to 0.1µA. Switch SD between VDD and GND for minimum cur-
rent consumption in shutdown. The LM48556 may be dis-
abled with shutdown voltages less than 0.45V, however, the
idle current will be greater than the typical 0.1µA value.
PROPER SELECTION OF EXTERNAL COMPONENTS
Power Supply Bypassing/Filtering
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. Place a 4.7µF tantalum
capacitor in parallel with a 0.1µF ceramic capacitor from
VDD to GND. Additional bulk capacitance may be added as
required.
Charge Pump Capacitor Selection
Use low ESR ceramic capacitors (less than 100mΩ) for opti-
mum performance.
Charge Pump Flying Capacitor (C1)
The flying capacitor (C1) affects the load regulation and out-
put impedance of the charge pump. A C1 value that is too low
results in a loss of current drive, leading to a loss of amplifier
headroom. A higher valued C1 improves load regulation and
lowers charge pump output impedance to an extent. Above
4.7µF, the RDS(ON) of the charge pump switches and the ESR
of C1 and CSS dominate the output impedance. A lower value
capacitor can be used in systems with low maximum output
power requirements.
Charge Pump Hold Capacitor (CSS)
The value and ESR of the hold capacitor (CSS) directly affects
the ripple on CPVSS. Increasing the value of CSS reduces out-
put ripple. Decreasing the ESR of CSS reduces both output
ripple and charge pump output impedance. A lower value ca-
pacitor can be used in systems with low maximum output
power requirements.
Gain Setting Resistor Selection
The amplifier gain of the LM48556 is set by four external re-
sistors, two per each input, RIN_ and RF_ (Figure 1). The
amplifier gain is given by equation (1):
AV = RF / RIN (V/V)
(1)
Careful matching of the resistor pairs, RF+ and RF-, and RIN+
and RIN-, is required for optimum performance. Any mismatch
between the resistors results in a differential gain error that
leads to an increase in THD+N, decrease in PSRR and CM-
RR, as well as an increase in output offset voltage. Resistors
with a tolerance of 1% or better are recommended.
The gain setting resistors should be placed as close to the
device as possible. Keeping the input traces close together
and of the same length increases noise rejection in noisy en-
vironments. Noise coupled onto the input traces which are
physically close to each other will be common mode and eas-
ily rejected.
Feedback Capacitor Selection
Due to their capacitive nature, ceramic speakers poorly re-
produce high frequency audio content. At high frequencies, a
ceramic speaker presents a low impedance load to the am-
plifier, increasing the required drive current. The higher output
current can drive the device into clipping, increasing THD+N.
Low-pass filtering the audio signal improves audio quality by
decreasing the signal amplitude at high frequencies, reducing
the speaker drive current. Adding a capacitor in parallel with
each feedback resistor creates a simple low-pass filter with
the -3dB point determined by equation (2):
f−3dB = 1 / 2πRFCF (Hz)
(2)
Where RF is the value of the feedback resistor determined by
equation (1) in the Gain Setting Resistors Selection section,
and CF is the value of the feedback capacitor. The feedback
capacitor is optional and not required for normal operation.
Input Capacitor Selection
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 LM48556. The input
capacitors create a high-pass filter with the input resistors
RIN. The -3dB point of the high pass filter is found using Equa-
tion (3) below.
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| PDF Descargar | [ Datasheet LM48556.PDF ] | |
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