LM48510SD/NOPB National Semiconductor, LM48510SD/NOPB Datasheet - Page 10

IC AMP AUDIO PWR 1.9W MONO 16LLP

LM48510SD/NOPB

Manufacturer Part Number
LM48510SD/NOPB
Description
IC AMP AUDIO PWR 1.9W MONO 16LLP
Manufacturer
National Semiconductor
Series
Boomer®, PowerWise®r
Type
Class Dr
Datasheet

Specifications of LM48510SD/NOPB

Output Type
1-Channel (Mono)
Max Output Power X Channels @ Load
1.9W x 1 @ 4 Ohm
Voltage - Supply
2.7 V ~ 5 V
Features
Depop, Differential Inputs, PWM, Short-Circuit and Thermal Protection, Shutdown
Mounting Type
Surface Mount
Package / Case
16-LLP
Amplifier Class
D
No. Of Channels
1
Output Power
1.2W
Supply Voltage Range
2.7V To 5V
Load Impedance
8ohm
Operating Temperature Range
-40°C To +85°C
Amplifier Case Style
LLP
Rohs Compliant
Yes
For Use With
LM48510SDBD - BOARD EVALUATION LM48510SD
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
LM48510SDTR
www.national.com
Application Information
GENERAL AMPLIFIER FUNCTION
The audio amplifier portion of LM48510 is a Class D featuring
a filterless modulation scheme. The differential outputs of the
device switch at 300kHz from PV
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 Class D 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 Class D 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 oc-
curs, 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.
OPERATING RATINGS
The LM48510 has independent power supplies for the Class
D audio power amplifier (PV
(V
V
Note the output voltage (PV
DIFFERENTIAL AMPLIFIER EXPLANATION
As logic supply voltages continue to shrink, designers are in-
creasingly turning to differential analog signal handling to
preserve signal to noise ratios with restricted voltage swing.
The amplifier portion of the LM48510 is a fully differential am-
plifier that features differential input and output stages. 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 in signal to noise ratio relative to differential inputs. The
amplifier also offers the possibility of DC input coupling which
eliminates the two external AC coupling, DC blocking capac-
itors. The amplifier 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 amplifier portion of the LM48510 simply am-
plifies the difference between the signals. A major benefit of
a differential amplifier is the improved common mode rejec-
tion 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.
AMPLIFIER DISSIPATION
In general terms, efficiency is considered to be the ratio of
useful work output divided by the total energy required to pro-
duce it with the difference being the power dissipated, typi-
cally, in the IC. The key here is “useful” work. For audio
systems, the energy delivered in the audible bands is con-
sidered 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 be-
ing transduced is dissipated in the LM48510 and in the trans-
ducer load. The amount of power dissipation in the LM48510
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
1
DD
)
). The Class D amplifier operating rating is 2.4V
5.5V when being used without the Boost.
1
, V
1
, V
1
) has to be more than V
1
1
) and the Boost Converter
to GND. When there is no
(PV
DD
.
1
,
10
output power. The amplifier dissipates only a fraction of the
excess power requiring no additional PCB area or copper
plane to act as a heat sink.
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON time of the FET
means the maximum output current will be determined by
power dissipation within the boost converter FET switch. The
switch power dissipation from ON-state conduction is calcu-
lated by Equation 1.
Where DC is the duty cycle.
There will be some switching losses as well, so some derating
needs to be applied when calculating IC power dissipation.
SHUTDOWN FUNCTION
To reduce power consumption while not in use, the amplifier
of LM48510 contains shutdown circuitry that reduces current
draw to less than 0.01µA. It is best to switch between ground
and supply (PV
shutdown state. While the LM48510 may be disabled with
shutdown voltages in between ground and supply, the idle
current will be greater than the typical 0.01µA value. In-
creased THD may also be observed with voltages less than
V
The amplifier has an internal resistor connected between
GND and SD
inate any unwanted state changes when the SD
floating. The amplifier will enter the shutdown state when the
SD
voltage has crossed the threshold. To minimize the supply
current while in the shutdown state, the SD
driven to GND or left floating. If the SD
GND, the amount of additional resistor current due to the in-
ternal shutdown resistor can be found by Equation (2) below.
With only a 0.5V difference, an additional 1.7µA of current will
be drawn while in the shutdown state.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry to provide a
quick, smooth transition into shutdown. Another solution is to
use a single-pole, single-throw switch, and a pull-up resistor.
One terminal of the switch is connected to GND. The other
side is connected to the two shutdown pins and the terminal
of the pull-up resistor. The remaining resistance terminal is
connected to V
up resistor connected to V
scheme guarantees that the shutdown pins will not float thus
preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using
integrated power amplifiers, and switching DC-DC convert-
ers, is critical for optimizing device and system performance.
Consideration to component values must be used to maxi-
mize overall system quality.
The best capacitors for use with the switching converter por-
tion of the LM48510 are multi-layer ceramic capacitors. They
have the lowest ESR (equivalent series resistance) and high-
DD
AMP
on the SD
P
pin is left floating or if not floating, when the shutdown
DMAX(SWITCH)
AMP
AMP
DD
1
, V
(V
. If the switch is open, then the external pull-
pins. The purpose of this resistor is to elim-
pin when in PLAY mode.
SD
1
) for minimum current usage while in the
= DC x I
- GND) / 300kΩ
DD
IND
will enable the LM48510. This
(AVE)
2
AMP
x R
pin is not driven to
DS(ON)
AMP
pin should be
AMP
pin is
(1)
(2)

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