max9791 Maxim Integrated Products, Inc., max9791 Datasheet - Page 24

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

Windows Vista-Compliant Class D Speaker
Amplifiers with DirectDrive Headphone Amplifiers
PVDD powers the speaker amplifiers. PVDD ranges
from 4.5V to 5.5V. Bypass PVDD with a 0.1µF capacitor
to PGND. Apply additional bulk capacitance at the
device if long input traces between PVDD and the
power source are used.
The headphone amplifiers are powered from HPVDD
and CPVSS. HPVDD is the positive supply of the head-
phone amplifiers and ranges from 2.7V to 5.5V. Bypass
HPVDD with a 10µF capacitor to PGND. CPVSS is the
negative supply of the headphone amplifiers. Bypass
CPVSS with a 1µF capacitor to PGND. The charge
pump inverts the voltage at HPVDD, and the resulting
voltage appears at CPVSS. A 1µF capacitor should be
connected between C1N and C1P.
The internal LDO and the remainder of the device are
powered by AVDD. AVDD ranges from 4.5V to 5.5V.
Bypass AVDD with a 0.1µF capacitor to GND and two
1µF capacitors to GND. Note additional bulk capaci-
tance is required at the device if long input traces
between AVDD and the power source are used.
The input capacitor (C
amplifier input resistance (R
that removes the DC bias from the incoming signal.
Figure 12. Input Coupling Capacitor-Induced THD+N vs.
Frequency
24
______________________________________________________________________________________
Speaker Amplifier Power-Supply Input (PVDD)
Positive Power Supply and LDO Input (AVDD)
-100
-50
-60
-70
-80
-90
INPUT COUPLING CAPACITOR-INDUCED THD+N
Headphone Amplifier Power-Supply Input
10
0402 6.3V X5R 10% 1μF
vs. FREQUENCY (HEADPHONE MODE)
0603 10V X7R 10% 1μF
FREQUENCY (kHz)
IN_
0603 10V X5R 10% 1μF
Component Selection
), in conjunction with the
IN_
100
0805 50V X7R 10% 1μF
), forms a highpass filter
(HPVDD and CPVSS)
V
FS = 1V
R
OUT
L
=32Ω
- -3dBFS
RMS
Input Filtering
1000
The AC-coupling capacitor allows the amplifier to bias
the signal to an optimum DC level. Assuming zero
source impedance, the -3dB point of the highpass filter
is given by:
R
Choose C
quency of interest. Setting f
fier’s low frequency response. Use capacitors with
adequately low-voltage coefficient dielectrics (see Figure
12). Capacitors with higher voltage coefficients, such as
ceramics, result in increased distortion at low frequencies.
Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric.
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability
to provide sufficient current drive, which leads to a loss
of output voltage. Connect a 1µF capacitor between
C1P and C1N.
Figure 13. Speaker RF Immunity
IN_
is the amplifier’s external input resistance value.
IN_
-100
-110
-120
-130
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
such that f
0
f
500
-3
Charge-Pump Capacitor Selection
SPEAKER RF IMMUNITY
dB
1000
vs. FREQUENCY
=
FREQUENCY (MHz)
-3dB
RIGHT
2
-3dB
π
LEFT
1500
R
is well below the lowest fre-
IN
too high affects the ampli-
1
_
C
2000
Flying Capacitor (C1)
IN
_
2500
3000