max9791 Maxim Integrated Products, Inc., max9791 Datasheet - Page 23

• Manufacturer Part Number: max9791
• Description: Windows Vista-compliant Class D Speaker Amplifiers With Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

External input resistors in conjunction with the internal
feedback resistors (R
gain of the MAX9791/MAX9792. Set gain by using
resistor R
where A
20kΩ yields a gain of 4V/V, or 12dB.
In applications where speaker leads exceed 15cm, use
a filter constructed from a ferrite bead and a capacitor
to ground (Figure 10) to provide additional EMI sup-
pression. Use a ferrite bead with low DC resistance,
high frequency (> 1.2MHz) impedance of 100Ω to
600Ω, and rated for at least 1A. The capacitor value
varies based on the ferrite bead chosen and the actual
speaker lead length. Select the capacitor value based
on EMI performance.
The headphone amplifiers are specified for the worst-
case scenario when both inputs are in phase. Under
this condition, the drivers simultaneously draw current
from the charge pump, leading to a slight loss in head-
room of CPVSS. In typical stereo audio applications, the
left and right signals have differences in both magni-
tude and phase, subsequently leading to an increase in
the maximum attainable output power. Figure 11 shows
the two extreme cases for in and out of phase. In most
cases, the available power lies between these
extremes.
External input resistors in conjunction with the internal
feedback resistors (R
gain of the MAX9791/MAX9792. Set gain by using
resistor R
where A
40.2kΩ yields a gain of 1V/V, or 0dB.
Amplifiers with DirectDrive Headphone Amplifiers
Output Power (Headphone Amplifier)
VSPKR
VHP
IN1
IN2
as follows (Figure 9):
(Figure 4) as follows:
is the desired voltage gain. An R
A
is the desired voltage gain. An R
VSPKR
Windows Vista-Compliant Class D Speaker
A
______________________________________________________________________________________
VHP
FHP
Headphone Amplifier Gain
FSPKR
Setting Speaker Amplifier Gain
=
=
-4
-
) set the headphone amplifier
Optional Ferrite Bead Filter
⎛
⎝ ⎜
⎛
⎝ ⎜
Component Selection
40 2
) set the speaker amplifier
20
R
R
IN
.
IN
k
Gain-Setting Resistors
Ω
1
k
2
Ω
⎞
⎠ ⎟
⎞
⎠ ⎟
V V
V V
/
/
IN2
IN1
of
of
The MAX9791/MAX9792 speaker amplifiers are pow-
ered from PVDD with a range from 4.5V to 5.5V. The
headphone amplifiers are powered from HPVDD and
CPVSS. HPVDD is the positive supply of the headphone
amplifiers and charge pump ranging from 2.7V to 5.5V.
CPVSS is the negative supply of the headphone ampli-
fiers. The charge pump inverts the voltage at HPVDD,
and the resulting voltage appears at CPVSS. AVDD
powers the remainder of the device.
Figure 10. Optional Ferrite Bead Filter
Figure 11. Output Power vs. Supply Voltage with Inputs In/Out
of Phase; 32W Load Conditions and 3.5dB Gain
*L1 = L2 = WÜRTH 742792040
0.001
0.01
MAX9791A/B
100
0.1
MAX9792A
10
1
vs. OUTPUT POWER (HEADPHONE MODE)
TOTAL HARMONIC DISTORTION + NOISE
0
R
L
= 32Ω
50
IN PHASE
OUTPUT POWER (mW)
OUT OF PHASE
100
L1*
L2*
150
Power Supplies
200
330pF
250
330pF
23