MAX9755 Maxim Integrated Products, MAX9755 Datasheet - Page 19

• Manufacturer Part Number: MAX9755
• Description: 2.6W Stereo Audio Power Amplifiers and DirectDrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products

The MAX9750/MAX9751/MAX9755 feature speaker
amplifiers designed to drive a load differentially, a con-
figuration referred to as bridge-tied load (BTL). The BTL
configuration (Figure 9) offers advantages over the sin-
gle-ended configuration, where one side of the load is
connected to ground. Driving the load differentially
doubles the output voltage compared to a single-
ended amplifier under similar conditions. Thus, the
device’s differential gain is twice the closed-loop gain
of the input amplifier. The effective gain is given by:
Substituting 2 X V
yields four times the output power due to double the
output voltage:
Since the differential outputs are biased at midsupply,
there is no net DC voltage across the load. This elimi-
nates the need for DC-blocking capacitors required for
single-ended amplifiers. These capacitors can be large
and expensive, can consume board space, and can
degrade low-frequency performance.
Figure 9. Bridge-Tied Load Configuration
Applications Information
P
V
2.6W Stereo Audio Power Amplifiers and
______________________________________________________________________________________
+1
-1
OUT(P-P)
OUT
RMS
A
VD
=
=
= ×
BTL Speaker Amplifiers
V
V
2
RMS
OUT P P
R
into the following equation
2 2
L
R
R
(
2
IN
F
−
DirectDrive Headphone Amplifiers
)
V
2 x V
V
OUT(P-P)
OUT(P-P)
OUT(P-P)
Under normal operating conditions, the MAX9750/
MAX9751/MAX9755 can dissipate a significant amount
of power. The maximum power dissipation for each
package is given in the Absolute Maximum Ratings
under Continuous Power Dissipation, or can be calcu-
lated by the following equation:
where T
ture, and θ
°C/W as specified in the Absolute Maximum Ratings
section. For example, θ
+42°C/W. For optimum power dissipation, the exposed
paddle of the package should be connected to the
ground plane (see the Layout and Grounding section).
The increase in power delivered by the BTL configura-
tion directly results in an increase in internal power dis-
sipation over the single-ended configuration. The
maximum power dissipation for a given V
given by the following equation:
If the power dissipation for a given application exceeds
the maximum allowed for a given package, either reduce
V
temperature, or add heatsinking to the device. Large
output, supply, and ground PC board traces improve the
maximum power dissipation in the package.
Figure 10. Total Harmonic Distortion Plus Noise vs. Output Power
with Inputs In/Out of Phase (Headphone Mode)
DD
, increase load impedance, decrease the ambient
J(MAX)
Power Dissipation and Heat Sinking
0.001
1000
JA
0.01
100
Output Power (Speaker Amplifier)
0.1
10
P
1
DISSPKG MAX
is the reciprocal of the derating factor in
0
is +150°C, T
V
R
A
P
DD
L
V
DISS MAX
= 16Ω
= 3dB
= 5V
25
(
OUTPUTS IN PHASE
(
OUTPUT POWER (mW)
JA
50
OUTPUTS 180° OUT OF PHASE
)
of the thin QFN package is
)
=
A
=
T
75
2
J MAX
is the ambient tempera-
π
(
V
2
DD
R
θ
www.DataSheet4U.com
100
JA
L
2
)
−
T
125
A
DD
and load is
150
19