LM4927SDBD National Semiconductor, LM4927SDBD Datasheet - Page 11

• Manufacturer Part Number: LM4927SDBD
• Description: BOARD EVALUATION LM4927SD
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4927SDBD

• Amplifier Type: Class AB
• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 2.5W x 1 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4927
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation versus a single-ended amplifier
operating at the same conditions.
Since the LM4927 has bridged outputs, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier. Even with this substantial increase in power dissipa-
tion, the LM4927 does not require additional heatsinking
under most operating conditions and output loading. From
Equation 3, assuming a 5V power supply and an 8Ω load,
the maximum power dissipation point is 625mW. The maxi-
mum power dissipation point obtained from Equation 3 must
not be greater than the power dissipation results from Equa-
tion 4:
The LM4927’s θ
pending on the ambient temperature, T
surroundings, Equation 4 can be used to find the maximum
internal power dissipation supported by the IC packaging. If
the result of Equation 3 is greater than that of Equation 4,
then either the supply voltage must be decreased, the load
impedance increased, the ambient temperature reduced, or
the θ
traces near the output, V
lower the θ
heatsinking allowing higher power dissipation. For the typical
application of a 5V power supply, with an 8Ω load, the
maximum ambient temperature possible without violating the
maximum junction temperature is approximately 110˚C pro-
vided that device operation is around the maximum power
dissipation point. Recall that internal power dissipation is a
function of output power. If typical operation is not around the
maximum power dissipation point, the LM4927 can operate
at higher ambient temperatures. Refer to the Typical Per-
formance Characteristics curves for power dissipation in-
formation.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor location on both the
bypass and power supply pins should be as close to the
device as possible. A larger half-supply bypass capacitor
improves PSRR because it increases half-supply stability.
Typical applications employ a 5V regulator with 10µF and
0.1µF bypass capacitors that increase supply stability. This,
however, does not eliminate the need for bypassing the
supply nodes of the LM4927. The LM4927 will operate with-
out the bypass capacitor C
crease. A 1µF capacitor is recommended for C
maximizes PSRR performance. Lesser values may be used,
but PSRR decreases at frequencies below 1kHz. The issue
of C
click and pop performance as explained in the section
Proper Selection of External Components.
B
JA
selection is thus dependant upon desired PSRR and
P
reduced with heatsinking. In many cases, larger
P
DMAX
JA
DMAX
. The larger areas of copper provide a form of
= 4 * (V
P
JA
= (V
DMAX
in an SDA08A package is 63˚C/W. De-
DD
DD
= (T
)
2
DD
)
/ (2π
2
, and GND pins can be used to
B
JMAX
/ (2π
, although the PSRR may de-
2
R
2
- T
L
R
) Single-Ended
L
A
) Bridge Mode
) / θ
JA
A
(Continued)
, of the system
B
. This value
(2)
(3)
(4)
11
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4927 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. The device may then be placed
into shutdown mode by toggling the Shutdown Select pin to
logic low. The trigger point for shutdown is shown as a typical
value in the Supply Current vs Shutdown Voltage graphs in
the Typical Performance Characteristics section. It is best
to switch between ground and supply for maximum perfor-
mance. While the device may be disabled with shutdown
voltages in between ground and supply, the idle current may
be greater than the typical value of 0.1µA. In either case, the
shutdown pin should be tied to a definite voltage to avoid
unwanted state changes.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry, which pro-
vides a quick, smooth transition to shutdown. Another solu-
tion is to use a single-throw switch in conjunction with an
external pull-up resistor. This scheme guarantees that the
shutdown pin will not float, thus preventing unwanted state
changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical when optimizing
device and system performance. Although the LM4927 is
tolerant to a variety of external component combinations,
consideration of component values must be made when
maximizing overall system quality.
The LM4927 is unity-gain stable, giving the designer maxi-
mum system flexibility. The LM4927 should be used in low
closed-loop gain configurations to minimize THD+N values
and maximize signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power.
Input signals equal to or greater than 1Vrms are available
from sources such as audio codecs. Please refer to the
Audio Power Amplifier Design section for a more complete
explanation of proper gain selection. When used in its typical
application as a fully differential power amplifier the LM4927
does not require input coupling capacitors for input sources
with DC common-mode voltages of less than V
allowable input common-mode voltage levels are actually a
function of V
Equation 5:
Special care must be taken to match the values of the input
resistors (R
anced nature of differential amplifiers, resistor matching dif-
ferences can result in net DC currents across the load. This
DC current can increase power consumption, internal IC
power dissipation, reduce PSRR, and possibly damaging the
loudspeaker. The chart below demonstrates this problem by
showing the effects of differing values between the feedback
resistors while assuming that the input resistors are perfectly
matched. The results below apply to the application circuit
shown in Figure 1, and assumes that V
the system has DC coupled inputs tied to ground.
V
CMi
i1
<
DD
and R
(V
, R
DD
i
-1.2)*((R
, and R
i2
) to each other. Because of the bal-
-R
F
/ R
f
f
+(R
I
and may be determined by
= A
i
)/(R
VD
f
)-V
DD
DD
= 5V, R
*(R
i
/ 2R
www.national.com
L
DD
= 8Ω, and
f
)
. Exact
(5)
(6)