MAX9789AETJ+ Maxim Integrated Products, MAX9789AETJ+ Datasheet - Page 15

• Manufacturer Part Number: MAX9789AETJ+
• Description: IC AMP AUDIO 2W STER AB 32TQFN
• Manufacturer: Maxim Integrated Products
• Series: DirectDrive™r
• Type: Class ABr

Specifications of MAX9789AETJ+

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 2W x 2 @ 4 Ohm; 100mW x 2 @ 16 Ohm
• Voltage - Supply: 4.5 V ~ 5.5 V
• Features: Depop, Mute, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Product: Class-AB
• Output Power: 2 W
• Thd Plus Noise: 0.004 %
• Supply Current: 0.1 mA
• Maximum Power Dissipation: 1990 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Audio Load Resistance: 4 Ohms
• Minimum Operating Temperature: - 40 C
• Amplifier Class: AB
• No. Of Channels: 3
• Supply Voltage Range: 4.5V To 5.5V
• Load Impedance: 4ohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: TQFN
• Rohs Compliant: Yes
• For Use With: MAX9789AEVKIT+ - EVALUATION KIT FOR MAX9789A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Windows Vista-Compliant, Stereo Class AB Speaker
The output voltage is set by the following equation:
where V
To simplify resistor selection:
Since the input bias current at LDO_SET is typically
less than 500nA (max), large resistance values can be
used for R1 and R2 to minimize power consumption
without compromising accuracy. The parallel combina-
tion of R1 and R2 should be less than 1MΩ.
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage
(V
capacitors are needed to block this DC bias from the
headphones. Without these capacitors, a significant
amount of DC current flows to the headphone, resulting
in unnecessary power dissipation and possible dam-
age to both headphone and headphone amplifier.
Maxim’s DirectDrive architecture uses a charge pump
to create an internal negative supply voltage. It allows
the MAX9789/MAX9790 headphone amplifier output to
be biased about GND. With no DC component, there is
no need for the large DC-blocking capacitors. Instead
Figure 1. Adjustable Output Using External Feedback
Resistors.
DD
/ 2) for maximum dynamic range. Large coupling
Amplifiers and DirectDrive Headphone Amplifiers
LDO_SET
MAX9789
V
LDO OUT
LDO_OUT
R
LDO_SET
= 1.21V.
_
1
______________________________________________________________________________________
=
GND
R
2
⎛
⎜
⎝
=
V
V
LDO OUT
LDO SET
1 21
R2
R1
.
_
_
−
⎛
⎜
⎝
1
1
⎞
⎟
⎠
+
R
R
1μF
2
DirectDrive
1
⎞
⎟
⎠
TO HDA
CODEC
1μF
of two large capacitors (330µF typically required to
meet Vista magnitude response specifications), the
MAX9789/MAX9790 charge pump requires only two
small 1µF ceramic capacitors, conserving board
space, reducing cost, and improving the low-frequency
response of the headphone amplifier.
Previous attempts to eliminate the output coupling
capacitors involved biasing the headphone return
(sleeve) to the DC bias voltage of the headphone
amplifiers. This method raised some issues:
• The sleeve is typically grounded to the chassis.
• During an ESD strike, the amplifier’s ESD structures
• When using the headphone jack as a line out to
In addition to the cost and size disadvantages, the DC-
blocking capacitors limit the low-frequency response of
the amplifier and distort the audio signal:
• The impedance of the headphone load and the DC-
• The highpass filter is required by conventional single-
Using this biasing approach, the sleeve must be iso-
lated from system ground, complicating product
design.
are the only path to system ground. The amplifier
must be able to withstand the full ESD strike.
other equipment, the bias voltage on the sleeve may
conflict with the ground potential from other equip-
ment, resulting in large ground loop current and
possible damage to the amplifiers.
blocking capacitor form a highpass filter with the
-3dB point determined by:
where R
C
ended, single-supply headphone amplifier to block
the midrail DC component of the audio signal from the
headphones. Depending on the -3dB point, the filter
can attenuate low-frequency signals within the audio
band. Larger values of C
but are physically larger, more expensive capacitors.
Figure 2 shows the relationship between the size of
C
Note the Vista’s magnitude response specification
calls for a -3dB point at 20Hz at the headphone jack.
The -3dB point at 20Hz for a 32Ω headphone requires
a 330µF blocking capacitor (Table 2).
OUT
OUT
is the value of the DC-blocking capacitor.
and the resulting low-frequency attenuation.
L
is the impedance of the headphone and
f
−
3
dB
=
2π
Low-Frequency Response
OUT
R C
L OUT
1
reduce the attenuation,
15