LM4816MTBD National Semiconductor, LM4816MTBD Datasheet - Page 11

• Manufacturer Part Number: LM4816MTBD
• Description: BOARD EVALUATION LM4816MT
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4816MTBD

• Amplifier Type: Class AB
• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 1.5W x 2 @ 8 Ohm
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4816
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches 1/2 V
BYPASS pin is stable, the device becomes fully operational.
Although the bypass pin current cannot be modified, chang-
ing the size of C
magnitude of "clicks and pops". Increasing the value of C
reduces the magnitude of turn-on pops. However, this pre-
sents a tradeoff: as the size of C
increases. There is a linear relationship between the size of
C
for various values of C
In order eliminate "clicks and pops", all capacitors must be
discharged before turn-on. Rapidly switching V
allow the capacitors to fully discharge, which may cause
"clicks and pops".
NO LOAD STABILITY
The LM4816 may exhibit low level oscillation when the load
resistance is greater than 10kΩ. This oscillation only occurs
as the output signal swings near the supply voltages. Pre-
vent this oscillation by connecting a 5kΩ between the output
pins and ground.
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the Typical Performance Char-
acteristics section. Another way, using Equation (4), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac-
count for the amplifier’s dropout voltage, two additional volt-
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics curves, must be
added to the result obtained by Equation (8). The result in
Equation (9).
B
Power Output:
Load Impedance:
Input Level:
Input Impedance:
and the turn-on time. Here are some typical turn-on times
Bandwidth:
B
alters the device’s turn-on time and the
C
0.01µF
0.22µF
0.47µF
B
0.1µF
1.0µF
B
:
DD
. As soon as the voltage on the
B
100Hz−20 kHz
increases, the turn-on time
T
200 ms
440 ms
940 ms
ON
20 ms
2 Sec
(Continued)
DD
±
0.25 dB
may not
1W
1V
20kΩ
RMS
RMS
8Ω
(8)
B
11
The Output Power vs Supply Voltage graph for an 8Ω load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4816 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation section.
After satisfying the LM4816’s power dissipation require-
ments, the minimum differential gain is found using Equation
(10).
Thus, a minimum gain of 2.83 allows the LM4816’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let A
The amplifier’s overall gain is set using the input (R
feedback (R
set at 20kΩ, the feedback resistor is found using Equation
(11).
The value of R
The last step in this design example is setting the amplifier’s
−3dB frequency bandwidth. To achieve the desired
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least one−fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the
desired limit. The results are an
and an
and C
bandpass frequency limit. Find the coupling capacitor’s
value using Equation (14).
the result is
Use a 0.39µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain, A
upper passband response limit. With A
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4816’s 3.5MHz GBWP. With
As mentioned in the External Components section, R
i
create a highpass filter that sets the amplifier’s lower
V
DD
f
) resistors. With the desired input impedance
≥ (V
f
1/(2π*20kΩ*20Hz) = 0.398µF
is 30kΩ.
F
H
OUTPEAK
f
L
= 20kHzx5 = 100kHz
= 100Hz/5 = 20Hz
R
f
/R
i
+ (V
= A
VD
VD
OD TOP
= 3.
/2
+ V
VD
VD
OD BOT
, determines the
= 3 and f
))
www.national.com
±
±
0.25dB
0.25dB
i
) and
(10)
(12)
(13)
(14)
(15)
(11)
H
(9)
=
i