MAX9751 Maxim Integrated Products, Inc., MAX9751 Datasheet - Page 20

• Manufacturer Part Number: MAX9751
• Description: 2.6w Stereo Audio Power Amplifiers And Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

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.
2.6W Stereo Audio Power Amplifiers and
DirectDrive Headphone Amplifiers
Figure 9. Bridge-Tied Load Configuration
20
______________________________________________________________________________________
Applications Information
P
V
+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
−
)
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).
For 8Ω applications, the worst-case power dissipation
occurs when the output power is 1.1W/channel, resulting
in a power dissipation of about 1W. In this case, both the
TSSOP and TQFN packages can be used without violat-
ing the maximum power dissipation or exceeding the
thermal protection threshold. For 4Ω applications, the
TSSOP package may require heat-sinking or forced air
cooling to prevent the device from reaching its thermal
limit. The more thermally efficient TQFN package is sug-
gested for speaker loads less than 8Ω.
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
Figure 10. Total Harmonic Distortion Plus Noise vs. Output Power
with Inputs In/Out of Phase (Headphone Mode)
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
DD
L
V
= 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
J MAX
is the ambient tempera-
(
θ
100
JA
)
−
T
125
A
150