LM4940TS/NOPB National Semiconductor, LM4940TS/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM4940TS/NOPB
• Description: IC AMP AUDIO PWR 6W STER TO263-9
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4940TS/NOPB

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 6W x 2 @ 4 Ohm
• Voltage - Supply: 10 V ~ 16 V
• Features: Depop, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: TO-263-9 (9 leads + tab)
• For Use With: LM4940TSBD - BOARD EVALUATION LM4940TS
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM4940TS; *LM4940TS/NOPB; LM4940TS; LM4940TSNOPB; LM4940TSNOPB

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voltage or increasing the load resistance. Further allowance
should be made for increased ambient temperatures.
The above examples assume that a device is operating
around the maximum power dissipation point. Since internal
power dissipation is a function of output power, higher ambi-
ent temperatures are allowed as output power or duty cycle
decreases.
If the result of Equation (3) is greater than that of Equation (4),
then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further, en-
sure that speakers rated at a nominal 4Ω do not fall below
3Ω. If these measures are insufficient, a heat sink can be
added to reduce θ
ditional copper area around the package, with connections to
the ground pins, supply pin and amplifier output pins. Refer
to the Typical Performance Characteristics curves for pow-
er dissipation information at lower output power levels.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding
the voltage applied to any pin, with respect to ground, as listed
in the Absolute Maximum Ratings section.
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 voltage regulator typically use
a 10µF 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 capacitance connected between the LM4940's supply
pins and ground. Do not substitute a ceramic capacitor for the
tantalum. Doing so may cause oscillation. Keep the length of
leads and traces that connect capacitors between the
LM4940's power supply pin and ground as short as possible.
Connecting a 10µF capacitor, C
pin and ground improves the internal bias voltage's stability
and improves the amplifier's PSRR. The PSRR improve-
ments increase as the bypass pin capacitor value increases.
Too large, however, increases turn-on time and can compro-
mise the amplifier's click and pop performance. The selection
of bypass capacitor values, especially C
desired PSRR requirements, click and pop performance (as
explained in the section, SELECTING EXTERNAL COMPO-
NENTS), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4940 features an active-low shutdown mode that dis-
ables the amplifier's bias circuitry, reducing the supply current
to 40μA (typ). Connect SHUTDOWN to a voltage between 2V
to V
to disable the device. A voltage that is greater than GND can
increase shutdown current.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling ca-
pacitor: the lowest audio frequency that requires amplification
and desired output transient suppression.
DD
/2 for normal operation. Connect SHUTDOWN to GND
JA
. The heat sink can be created using ad-
BYPASS
, between the BYPASS
BYPASS
, depends on
12
As shown in Figure 3, the input resistor (R
capacitor (C
is found using Equation (7).
As an example when using a speaker with a low frequency
limit of 50Hz, C
C
ciency, full range speaker whose response extends below
30Hz.
Output Coupling Capacitor Value Selection
The capacitors C
DC bias voltage and couple the output AC signal to the am-
plifier loads also determine low frequency response. These
capacitors, combined with their respective loads create a
highpass filter cutoff frequency. The frequency is also given
by Equation (6).
Using the same conditions as above, with a 4Ω speaker,
C
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 LM4940 settles to quiescent operation, its value
is critical when minimizing turn-on pops. The slower the
LM4940'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 LM4940 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 LM4940's internal amplifiers are configured as
unity gain buffers and are disconnected from the AMP
AMP
connected between the BYPASS pin and GND in a controlled
manner. Ideally, the input and outputs track the voltage ap-
plied to the BYPASS pin. The gain of the internal amplifiers
remains unity until the voltage applied to the BYPASS pin.
The gain of the internal amplifiers remains unity until the volt-
age on the bypass pin reaches V
on the bypass pin is stable, the device becomes fully opera-
tional and the amplifier outputs are reconnected to their re-
spective output pins. Although the BYPASS pin current
cannot be modified, changing the size of C
device's turn-on time. Here are some typical turn-on times for
various values of C
INA
OUT
B
shown in
is 820µF (nearest common valve).
pins. An internal current source charges the capacitor
DD
DD
/2), the smaller the turn-on pop. Choosing C
/2 voltage present at the BYPASS pin ramps to its
IN
) produce a high pass filter cutoff frequency that
Figure 3
i
, using Equation (7) is 0.159µF. The 0.39µF
OUTA
BYPASS
f
C
and C
allows the LM4940 to drive high effi-
= 1/2
:
OUTB
π
R
DD
i
C
that block the V
i
/2. As soon as the voltage
BYPASS
BYPASS
IN
IN
BYPASS
, the capacitor
(in the range of
) and the input
IN
DD
determines
alters the
no larger
/2 output
BYPASS
A
and
(5)