LM4950TS National Semiconductor, LM4950TS Datasheet - Page 17

• Manufacturer Part Number: LM4950TS
• Description: Audio Power Amplifier IC
• Manufacturer: National Semiconductor

Specifications of LM4950TS

• Amplifier Case Style: TO-220
• No. Of Pins: 9
• Peak Reflow Compatible (260 C): No
• Termination Type: Through Hole
• Leaded Process Compatible: No
• Package / Case: 9-TO-220
• Operational Class: Class-AB
• Audio Amplifier Function: Speaker
• Input Offset Voltage: 30@12VmV
• Total Harmonic Distortion: 0.05@4Ohm@2.5W%
• Single Supply Voltage (typ): 12/15V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 70dB
• Single Supply Voltage (min): 9.6V
• Single Supply Voltage (max): 16V
• 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: 9 +Tab
• Package Type: TO-263
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling
capacitor: the lowest audio frequency that requires amplifi-
cation and desired output transient suppression.
As shown in Figure 3, the input resistor (R
capacitor (C
that is found using Equation (7).
As an example when using a speaker with a low frequency
limit of 50Hz, C
C
efficiency, full range speaker whose response extends below
30Hz.
Bypass Capacitor Value
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
connected to the BYPASS pin. Since C
how fast the LM4950 settles to quiescent operation, its value
is critical when minimizing turn-on pops. The slower the
LM4950’s outputs ramp to their quiescent DC voltage (nomi-
nally V
equal to 10µF along with a small value of C
0.1µF to 0.39µF), produces a click-less and pop-less shut-
down function. As discussed above, choosing C
than necessary for the desired bandwidth helps minimize
clicks and pops.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4950 contains circuitry that eliminates turn-on and
shutdown transients ("clicks and pops"). For this discussion,
turn-on refers to either applying the power supply voltage or
when the micro-power shutdown mode is deactivated.
As the V
final value, the LM4950’s internal amplifiers are configured
as unity gain buffers and are disconnected from the AMP
and AMP
pacitor connected between the BYPASS pin and GND in a
INA
shown in Figure 3 allows the LM4950 to drive high
DD
DD
/2), the smaller the turn-on pop. Choosing C
B
/2 voltage present at the BYPASS pin ramps to its
pins. An internal current source charges the ca-
IN
) produce a high pass filter cutoff frequency
i
, using Equation (7) is 0.159µF. The 0.39µF
f
c
= 1/2πR
i
C
i
BYPASS
BYPASS
(Continued)
IN
IN
) and the input
, the capacitor
(in the range of
IN
determines
no larger
BYPASS
(7)
A
17
controlled manner. Ideally, the input and outputs track the
voltage applied to the BYPASS pin. The gain of the internal
amplifiers remains unity until the voltage applied to the BY-
PASS pin.
The gain of the internal amplifiers remains unity until the
voltage on the bypass pin reaches V
voltage on the bypass pin is stable, the device becomes fully
operational and the amplifier outputs are reconnected to
their respective output pins. Although the BYPASS pin cur-
rent cannot be modified, changing the size of C
the device’s turn-on time. Here are some typical turn-on
times 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".
There is a relationship between the value of C
C
is applied or the shutdown mode is deactivated. Best perfor-
mance is achieved by setting the time constant created by
C
given value of C
DRIVING PIEZO-ELECTRIC SPEAKER TRANSDUCERS
The LM4950 is able to drive capacitive piezo-electric trans-
ducer loads that are less than equal to 200nF. Stable opera-
tion is assured by placing 33pF capacitors in parallel with the
20kΩ feedback resistors. The additional capacitors are
shown in Figure 4.
When driving piezo-electric tranducers, sound quality and
accoustic power is entirely dependent upon a transducer’s
frequency response and efficiency. In this application, power
dissipated by the LM4950 is very low, typically less than
250mW when driving a 200nF piezo-electric transduce
(V
BYPASS
IN
DD
and R
= 12V).
that ensures minimum output transient when power
i
C
+ R
B
1.0
2.2
4.7
10
(µF)
f
BYPASS
to a value less than the turn-on time for a
as shown in the table above.
BYPASS
:
DD
T
/2. As soon as the
ON
120
120
200
440
(ms)
BYPASS
DD
www.national.com
may not
IN
alters
and