LM4946SQEVAL National Semiconductor, LM4946SQEVAL Datasheet - Page 27

• Manufacturer Part Number: LM4946SQEVAL
• Description: BOARD EVALUATION LM4946SQ
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4946SQEVAL

• Amplifier Type: Class D
• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.3W x 1 @ 8 Ohm; 85mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4946
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

the ground pin(s), supply pin and amplifier output pins. Ex-
ternal, solder attached SMT heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a
heat sink, the θ
junction-to-case thermal impedance, θ
thermal impedance, and θ
impedance). Refer to the Typical Performance Characteris-
tics curves for power dissipation information at lower output
power levels.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is crit-
ical for low noise performance and high power supply rejec-
tion. Applications that employ a 5V regulator typically use a
1µF in parallel with a 0.1µF filter capacitors to stabilize the
regulator's output, reduce noise on the supply line, and im-
prove the supply's transient response. However, their pres-
ence does not eliminate the need for a local 1.0µF tantalum
bypass capacitor and a parallel 0.1µF ceramic capacitor con-
nected between the LM4946's supply pin and ground. Keep
the length of leads and traces that connect capacitors be-
tween the LM4946's power supply pin and ground as short as
possible.
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 ef-
ficiency 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.
JA
is the sum of θ
SA
i
in Figures 1 & 2). A high value
is the sink-to-ambient thermal
JC
, θ
CS
CS
, and θ
is the case-to-sink
SA
. (θ
JC
is the
27
Applications using speakers with this limited frequency re-
sponse reap little improvement by using large input capacitor.
The internal input resistor (R
capacitor (C
is found using Equation (15).
As an example when using a speaker with a low frequency
limit of 150Hz, C
C
ciency, 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
to the BYPASS pin. Since C
LM4946 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4946's out-
puts ramp to their quiescent DC voltage (nominally V
the smaller the turn-on pop. Choosing C
with a small value of C
duces a click-less and pop-less shutdown function. As dis-
cussed above, choosing C
desired bandwidth helps minimize clicks and pops. C
should be in the range of 7 to 10 times the value of C
ensures that output transients are eliminated when power is
first applied or the LM4946 resumes operation after shut-
down.
i
shown in Figure 1 allows the LM4946 to drive high effi-
i
) produce a high pass filter cutoff frequency that
i
, using Equation (15) is 0.106µF. The 0.22µF
f
c
= 1 / (2πR
i
(in the range of 0.1µF to 0.33µF), pro-
i
no larger than necessary for the
i
), minimum 10kΩ, and the input
i
B
C
i
)
determines how fast the
B
, the capacitor connected
B
equal to 2.2µF along
www.national.com
B
's value
i
DD
. This
(15)
/2),