LM4846TL/NOPB National Semiconductor, LM4846TL/NOPB Datasheet - Page 26

• Manufacturer Part Number: LM4846TL/NOPB
• Description: IC AMP AUDIO PWR 1.15W AB 25USMD
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4846TL/NOPB

• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.15W x 1 @ 8 Ohm; 75mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: 3D, Depop, I²C, Mute, Shutdown, SPI, Thermal Protection, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 25-MicroSMD
• Operational Class: Class-AB
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.5@8Ohm@500mW%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Supply Current (max): 11@3.3VmA
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 88dB
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 25
• Package Type: uSMD
• For Use With: LM4846TLEVAL - BOARD EVALUATION LM4846TL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4846TLTR

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Application Information
LM4846’s supply pins and ground. Keep the length of leads
and traces that connect capacitors between the LM4846’s
power supply pin and ground as short as possible. Connect-
ing a 2.2µF capacitor, C
ground improves the internal bias voltage’s stability and
improves the amplifier’s PSRR. The PSRR improvements
increase as the bypass pin capacitor value increases. Too
large, however, increases turn-on time and can compromise
the amplifier’s click and pop performance. The selection of
bypass capacitor values, especially C
PSRR requirements, click and pop performance (as ex-
plained in the section, Proper Selection of External Compo-
nents), system cost, and size constraints.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
capacitor can be expensive and may compromise space
efficiency 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 large input capaci-
tor.
The internal input resistor (R
capacitor (C
is found using Equation (15).
i
) produce a high pass filter cutoff frequency that
B
, between the BYPASS pin and
i
in Figures 1 & 2). A high value
i
), nominal 20kΩ, and the input
B
, depends on desired
(Continued)
26
As an example when using a speaker with a low frequency
limit of 150Hz, C
0.22µF C
efficiency, full range speaker whose response extends below
40Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
nected to the BYPASS bump. Since C
the LM4846 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4846’s
outputs ramp to their quiescent DC voltage (nominally V
2), the smaller the turn-on pop. Choosing C
along with a small value of C
0.39µF), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
sary for the desired bandwidth helps minimize clicks and
pops. C
the value of C
eliminated when power is first applied or the LM4846 re-
sumes operation after shutdown.
B
’s value should be in the range of 5 times to 7 times
i
shown in Figure 1 allows the LM4846 to drive high
i
. This ensures that output transients are
i
, using Equation (15) is 0.053µF. The
f
c
= 1 / (2πR
i
(in the range of 0.1µF to
i
C
i
)
i
B
B
no larger than neces-
, the capacitor con-
determines how fast
B
equal to 1.0µF
(15)
DD
/