LM48520TL/NOPB National Semiconductor, LM48520TL/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM48520TL/NOPB
• Description: IC AMP AUDIO PWR 1.3W D 25USMD
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class Dr

Specifications of LM48520TL/NOPB

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 1.3W x 2 @ 8 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Differential Inputs, Short-Circuit Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 25-MicroSMD
• Operational Class: Class-D
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Output Power (typ): 1.3x2@8OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.04@8Ohm@500mW%
• Single Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (typ): 3/5V
• Power Supply Requirement: Triple
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 82dB
• Single Supply Voltage (min): Not RequiredV
• Single Supply Voltage (max): Not RequiredV
• Dual Supply Voltage (min): 2.4/2.7/3V
• Dual Supply Voltage (max): 5/5.5V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 25
• For Use With: LM48520TLBD - BOARD EVALUATION FOR LM48520TL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM48520TL; LM48520TL; LM48520TLTR

Application Information
GENERAL AMPLIFIER FUNCTION
The LM48520 features a Class D audio power amplifier that
utilizes a filterless modulation scheme, reducing external
component count, conserving board space and reducing sys-
tem cost. The outputs of the device transition from PV1 to
GND with a 300kHz switching frequency. With no signal ap-
plied, the outputs (V
cycle, in phase, causing the two outputs to cancel. This can-
cellation 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 LM48520 outputs changes. For increasing output voltage,
the duty cycle of V
decreases. For decreasing output voltages, the converse
occurs. The difference between the two pulse widths yields
the differential output voltage.
DIFFERENTIAL AMPLIFIER EXPLANATION
The amplifier portion of the LM48520 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 LM48520 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 AND EFFICIENCY
The major benefit of a Class D amplifier is increased efficiency
versus a Class AB. The efficiency of the LM48520 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.
REGULATOR POWER DISSIPATION
At higher duty cycles, the increased ON-time of the switch
FET means the maximum output current will be determined
by power dissipation within the LM48520 FET switch. The
switch power dissipation from ON-time conduction is calcu-
lated by:
Where DC is the duty cycle.
SHUTDOWN FUNCTION
The LM48520 features independent amplifier and regulator
shutdown controls, allowing each portion of the device to be
disabled or enabled independently. AmpSD controls the
P
D(SWITCH)
= DC x (I
LS+
LS+
INDUCTOR(AVE)
increases, while the duty cycle of V
and V
LS-
) switch with a 50% duty
)
2
x R
DS(ON)
(W)
(1)
LS-
11
Class D amplifiers, while BstSD controls the regulator. Driving
either inputs low disables the corresponding portion of the
device, and reducing supply current.
When the regulator is disabled, both FB_GND switches open,
further reducing shutdown current by eliminating the current
path to GND through the regulator feedback network. With the
regulator disabled, there is still a current path from V
through the inductor and diode, to the amplifier power supply.
This allows the amplifier to operate even when the regulator
is disabled. The voltage at PV1 and V1 will be:
Where V
the current through the inductor, and DCR is the DC resis-
tance of the inductor. Additionally, when the regulator is dis-
abled, an external voltage between 2.4V and 5.5V can be
applied directly to PV1 and V1 to power the amplifier.
It is best to switch between ground and V
rent consumption while in shutdown. The LM48520 may be
disabled with shutdown voltages in between GND and V
the idle current will be greater than the typical 0.1µA value.
Increased THD+N may also be observed when a voltage of
less than V
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 LM48520 are multi-layer ceramic capacitors. They
have the lowest ESR (equivalent series resistance) and high-
est resonance frequency, which makes them optimum for
high frequency switching converters.
When selecting a ceramic capacitor, only X5R and X7R di-
electric types should be used. Other types such as Z5U and
Y5F have such severe loss of capacitance due to effects of
temperature variation and applied voltage, they may provide
as little as 20% of rated capacitance in many typical applica-
tions. Always consult capacitor manufacturer’s data curves
before selecting a capacitor. High-quality ceramic capacitors
can be obtained from Taiyo-Yuden, AVX, and Murata.
POWER SUPPLY BYPASSING FOR AMPLIFIER
As with any amplifier, proper supply bypassing is critical for
low noise performance and high power supply rejection. The
capacitor location on both PV1, V1 and V
as close to the device as possible.
SELECTING INPUT CAPACITOR FOR AUDIO AMPLIFIER
Input capacitors, C
of the LM48520 forms a high pass filter that removes the DC
bias from an incoming signal. The AC-coupling capacitor al-
lows the amplifier to bias the signal to an optimal DC level.
Assuming zero source impedance, the -3dB point of the high
pass filter is given by:
Choose C
of interest. Setting f
sponses of the amplifier. Use capacitors with low voltage
D
IN
is the forward voltage of the Schottky diode, I
DD
such that f
is applied to AmpSD.
V
DD
f
(–3dB)
IN
-3dB
— [V
, in conjunction with the input impedance
-3dB
too high affects the low-frequency re-
= 1/2
D
is well below that lowest frequency
+ (I
π
L
R
x DCR)]
IN
C
IN
DD
DD
for minimum cur-
pins should be
www.national.com
L
DD
DD
(2)
(3)
is
,
,