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參數(shù)資料
| 型號： | MAX9789CETJ+T |
| 廠商： | Maxim Integrated Products |
| 文件頁數(shù)： | 7/28頁 |
| 文件大小： | 0K |
| 描述： | IC AMP AUDIO 2W STER AB 32TQFN |
| 產(chǎn)品培訓(xùn)模塊： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 標(biāo)準(zhǔn)包裝： | 2,500 |
| 系列： | DirectDrive® |
| 類型： | AB 類 |
| 輸出類型： | 2-通道（立體聲）帶立體聲耳機 |
| 在某負(fù)載時最大輸出功率 x 通道數(shù)量： | 2W x 2 @ 4 歐姆; 100mW x 2 @ 16 歐姆 |
| 電源電壓： | 4.5 V ~ 5.5 V |
| 特點： | 消除爆音，靜音，短路保護和熱保護，關(guān)機 |
| 安裝類型： | 表面貼裝 |
| 供應(yīng)商設(shè)備封裝： | 32-TQFN-EP（5x5） |
| 封裝/外殼： | 32-WFQFN 裸露焊盤 |
| 包裝： | 帶卷 (TR) |
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MAX9789/MAX9790
Windows Vista-Compliant, Stereo Class AB Speaker
Amplifiers and DirectDrive Headphone Amplifiers
______________________________________________________________________________________
15
The output voltage is set by the following equation:
where VLDO_SET = 1.21V.
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.
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage
(VDD / 2) for maximum dynamic range. Large coupling
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
of two large capacitors (330F typically required to
meet Vista magnitude response specifications), the
MAX9789/MAX9790 charge pump requires only two
small 1F 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.
Using this biasing approach, the sleeve must be iso-
lated from system ground, complicating product
design.
During an ESD strike, the amplifier’s ESD structures
are the only path to system ground. The amplifier
must be able to withstand the full ESD strike.
When using the headphone jack as a line out to
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.
Low-Frequency Response
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-
blocking capacitor form a highpass filter with the
-3dB point determined by:
where RL is the impedance of the headphone and
COUT is the value of the DC-blocking capacitor.
The highpass filter is required by conventional single-
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 COUT reduce the attenuation,
but are physically larger, more expensive capacitors.
Figure 2 shows the relationship between the size of
COUT and the resulting low-frequency attenuation.
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 330F blocking capacitor (Table 2).
f
RC
dB
L OUT
=
3
1
2
π
RR
VLDO OUT
12
121
1
=
_
.
VV
R
LDO OUT
LDO SET
__
=+
1
2
MAX9789
LDO_OUT
LDO_SET
GND
1
μF
R1
R2
1
μF
TO HDA
CODEC
Figure 1. Adjustable Output Using External Feedback
Resistors.
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