max9789a Maxim Integrated Products, Inc., max9789a Datasheet - Page 15

• Manufacturer Part Number: max9789a
• Description: Windows Vista-compliant, Stereo Class Ab Speaker Amplifiers And Directdrive Headphone Amplifiers Integrated Products
• Manufacturer: Maxim Integrated Products, Inc.

• The voltage coefficient of the capacitor, the change
• The combination of low-frequency attenuation and fre-
The MAX9789A/MAX9790A feature a low-noise charge
pump. The 550kHz switching frequency is well beyond
the audio range, and does not interfere with the audio
signals. The switch drivers feature a controlled switching
Figure 2. Low-Frequency Attenuation of Common DC-Blocking
Capacitor Values
Table 2. Low-Frequency Rolloff
*Vista requirement for 32 load.
in capacitance due to a change in the voltage
across the capacitor, distorts the audio signal. At
frequencies around the -3dB point, this effect is
maximized and the voltage coefficient appears as
frequency-dependent distortion. Figure 3 shows the
THD+N introduced by two different capacitor
dielectrics. Note that around the -3dB point, THD+N
increases dramatically.
quency-dependent distortion compromises audio
reproduction. DirectDrive improves low-frequency
reproduction in portable audio equipment that empha-
sizes low-frequency effects, such as multimedia lap-
tops, MP3, CD, and DVD players (See Table 2).
C
OUT
Windows Vista-Compliant, Stereo Class AB Speaker
330*
100
220
470
22
33
(µF)
Amplifiers and DirectDrive Headphone Amplifiers
-12
-15
-18
-21
-24
-27
-30
-3
-6
-9
0
1
______________________________________________________________________________________
LOW-FREQUENCY ROLLOFF
10
FREQUENCY (Hz)
R
100
(R
L
L
452
301
= 16Ω
99
45
30
21
= 16Ω)
33µF
100µF
220µF
DirectDrive
330µF
1k
f
-3dB
10k
(Hz)
Charge Pump
100k
R
L
226
151
= 32Ω
50
23
15
11
speed that minimizes noise generated by switching
transients. Limiting the switching speed of the charge
pump minimizes the di/dt noise caused by the parasitic
bond wire and trace inductance.
The MAX9789A/MAX9790A feature an internally gener-
ated, power-supply independent, common-mode bias
voltage of 1.8V referenced to GND. BIAS provides both
click-and-pop suppression and sets the DC bias level
for the amplifiers. The BIAS pin should be bypassed to
GND with a 1µF capacitor. No external load should be
applied to BIAS. Any load lowers the BIAS voltage,
affecting the overall performance of the device.
The MAX9789A/MAX9790A feature programmable
speaker amplifier gain, set by the logic voltages
applied to pins GAIN1 and GAIN2. Table 3 shows the
logic combinations that can be applied to pins GAIN1
and GAIN2 and their affects on the speaker amplifier
gain. The headphone amplifier gain is fixed at 3.5dB.
Figure 3. Distortion Contributed by DC-Blocking Capacitors
Table 3. MAX9789A/MAX9790A
Programmable Gain Settings
GAIN1
0
0
1
1
Headphone and Speaker Amplifier Gain
0.0001
0.001
GAIN2
0.01
0.1
10
1
0
1
0
1
10
MAX9789A/MAX9790A
ALUM/ELEC
ADDITIONAL THD+N DUE TO
DC-BLOCKING CAPACITORS
SPEAKER MODE
100
GAIN (dB)
FREQUENCY (Hz)
15.6
21.6
TANTALUM
10
6
1k
C
R
L
OUT
10k
= 16Ω
= 100µF
MODE GAIN (dB)
HEADPHONE
100k
3.5
3.5
3.5
3.5
BIAS
15