LM48580TLX/NOPB National Semiconductor, LM48580TLX/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM48580TLX/NOPB
• Description: IC AMP AUDIO SPEAKER DVR 12USMD
• Manufacturer: National Semiconductor
• Series: Boomer®, PowerWise®r
• Type: Class Hr

Specifications of LM48580TLX/NOPB

• Output Type: 1-Channel (Mono)
• Voltage - Supply: 2.5 V ~ 5.5 V
• Features: Differential Inputs, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 12-MicroSMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Max Output Power X Channels @ Load: -
• Other names: LM48580TLXTR

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Application Information
GENERAL AMPLIFIER FUNCTION
The LM48580 is a fully differential, Class H ceramic element
driver for ceramic speakers and haptic actuators. The inte-
grated, high efficiency boost converter dynamically adjusts
the amplifier’s supply voltage based on the output signal, in-
creasing headroom and improving efficiency compared to a
conventional Class AB driver. The fully differential amplifier
takes advantage of the increased headroom and bridge-tied
load (BTL) architecture, delivering significantly more voltage
than a single-ended amplifier.
PROPERTIES OF PIEZOELECTRIC ELEMENTS
Piezoelectric elements such as ceramic speakers or piezo-
electric haptic actuators are capacitive in nature. Due to their
capacitive nature, piezoelectric elements appear as low
impedance loads at high frequencies (typically above 5kHz).
A resistor in series with the piezoelectric element is required
to ensure the amplifier does not see a short at high frequen-
cies.
The value of the series resistor depends on the capacitance
of the element, the frequency content of the output signal, and
the desired frequency response. Higher valued resistors min-
imize power dissipation at high frequencies, but also impacts
the frequency response. This configuration is ideal for use
with haptic actuators, where the majority of the signal content
is typically below 2kHz. Conversely, lower valued resistors
maximize frequency response, while increasing power dissi-
pation at high frequency. This configuration is ideal for ce-
ramic speaker applications, where high frequency audio
content needs to be reproduced. Resistor values are typically
between 10Ω and 20Ω.
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM48580 features a fully differential amplifier. A differ-
ential amplifier amplifies the difference between the two input
FIGURE 4. Class H Operation
8
CLASS H OPERATION
Class H is a modification of another amplifier class (typically
Class B or Class AB) to increase efficiency and reduce power
dissipation. To decrease power dissipation, Class H uses a
tracking power supply that monitors the output signal and ad-
justs the supply accordingly. When the amplifier output is
below 3V
output increases above 3V
amplifier output as shown in Figure 4. When the amplifier out-
put falls below 3V
inal output voltage. Power dissipation is greatly reduced
compared to conventional Class AB drivers.
signals. A major benefit of the fully differential amplifier is the
improved common mode rejection ratio (CMRR) over single
ended input amplifiers. The increased CMRR of the differen-
tial amplifier reduces sensitivity to ground offset related noise
injection, especially important in noisy systems.
THERMAL SHUTDOWN
The LM48580 features thermal shutdown that protects the
device during thermal overload conditions. When the junction
temperature exceeds +160°C, the device is disabled. The
LM48580 remains disabled until the die temperature falls be-
low the +160°C and SHDN is toggled.
GAIN SETTING
The LM48580 features three internally configured gain set-
tings 18, 24, and 30dB. The device gain is selected through
a single pin (GAIN). The gain settings are shown in Table 2.
P-P
FLOAT
Gain
GND
VDD
, the nominal boost voltage is 6V. As the amplifier
P-P
TABLE 2. Gain Setting
, the boost converter returns to its nom-
30108021
P-P
, the boost voltage tracks the
Gain Setting
18dB
24dB
30dB