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| 型号： | MAX9879ERV+ |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 音频控制 |
| 英文描述： | Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier; Package: UCSP (R);30 pin;6 mm² ; Temperature: -40°C to +85°C |
| 中文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PBGA30 |
| 封装： | 2.50 X 3 MM, 0.50 MM PITCH, ROHS COMPLAINT, UCSP-30 |
| 文件页数： | 11/31页 |
| 文件大小： | 539K |
| 代理商： | MAX9879ERV+ |
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MAX9879
Stereo Class D Audio Subsystem
with DirectDrive Headphone Amplifier
______________________________________________________________________________________
19
Volume Control and Mute
The MAX9879 features three Volume Control registers
(see Table 4), allowing independent volume control of
speaker and headphone amplifier outputs. There is one
Speaker Volume Control register that evenly controls both
speaker outputs. Two Headphone Volume Control regis-
ters provide independent control of each headphone out-
put. Each volume control register provides 31 attenuation
steps providing 0dB to -75dB (typ) of total attenuation
and a mute function.
Class D Speaker Amplifier
The MAX9879 integrates a filterless Class D amplifier
that offers much higher efficiency than Class AB with-
out the typical disadvantages.
The high efficiency of a Class D amplifier is due to the
switching operation of the output stage transistors. In a
Class D amplifier, the output transistors act as current-
steering switches and consume negligible additional
power. Any power loss associated with the Class D out-
put stage is mostly due to the I2R loss of the MOSFET
on-resistance, and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output power. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9879 still exhibits 88% efficiency
under the same conditions (Figure 3).
Ultra-Low EMI Filterless Output Stage
In traditional Class D amplifiers, the high dV/dt of the
rising and falling edge transitions results in increased
EMI emissions, which requires the use of external LC
filters or shielding to meet EN55022 electromagnetic-
interference (EMI) regulation standards. Limiting the
dV/dt normally results in decreased efficiency. Maxim’s
active emissions limiting circuitry actively limits the
dV/dt of the rising and falling edge transitions, provid-
ing reduced EMI emissions, while maintaining up to
88% efficiency.
In addition to active emission limiting, the MAX9879 fea-
tures a spread-spectrum modulation mode that flattens
the wideband spectral components. Proprietary tech-
niques ensure that the cycle-to-cycle variation of the
switching period does not degrade audio reproduction
or efficiency (see the
Typical Operating Characteristics).
With spread-spectrum modulation, the switching fre-
quency varies randomly by ±40kHz around the center
frequency (700kHz). The effect is to reduce the peak
energy at harmonics of the switching frequency. Above
10MHz, the wideband spectrum looks like white noise for
EMI purposes (see Figure 4).
Speaker Current Limit
Most applications do not enter current limit unless the
output is short circuited or connected incorrectly.
When the output current of the speaker amplifier
exceeds the current limit (1.5A, typ) the MAX9879 dis-
ables the outputs for approximately 250s. At the end of
250s, the outputs are re-enabled, and if the fault condi-
tion still exists, the MAX9879 continues to disable and re-
enable the outputs until the fault condition is removed.
Bypass Mode
The integrated DPST analog audio switch allows the
MAX9879’s Class D amplifier to be bypassed. In bypass
mode, the Class D amplifier is automatically disabled
allowing an external amplifier to drive the speaker con-
nected between OUTL+ and OUTL- through RXIN+ and
RXIN- (see the
Typical Application Circuit).
The bypass switch is enabled at startup. The switch can
be opened or closed even when the MAX9879 is in soft-
ware shutdown (see the
I2C Register Description section).
Unlike discrete solutions, the switch design reduces
coupling of Class D switching noise to the RXIN_
inputs. This eliminates the need for a costly T-switch.
The bypass switch is typically used with two 10Ω resis-
tors connected to each input. These resistors, in combi-
nation with the switch on-resistance and an 8Ω load,
approximate the 32Ω load expected by the external
amplifier. Although not required, using the resistors
optimizes THD+N.
Drive RXIN+ and RXIN- with a low-impedance source
to minimize noise on the pins. In applications that do
not require the bypass mode, leave RXIN+ and RXIN-
unconnected.
MAX9877 EFFICIENCY
vs. IDEAL CLASS EFFICIENCY
MAX9877
fig03
OUTPUT POWER (W)
EFFICIENCY
(%)
0.75
0.50
0.25
10
20
30
40
50
60
70
80
90
100
0
1.00
MAX9879
IDEAL CLASS AB
VDD = PVDD_ = 3.7V (MAX9879)
VSUPPLY = 3.7V (IDEAL CLASS AB)
Figure 3. MAX9879 Efficiency vs. Class AB Efficiency
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相关代理商/技术参数 |
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| MAX9879ERV+T | 功能描述:音频放大器 Audio Subsystem w/DirectDrive RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| MAX9879EVKIT+ | 功能描述:音频放大器 Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| MAX987ESA | 功能描述:校验器 IC Single uPower Comparator RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
| MAX987ESA+ | 功能描述:校验器 IC Single uPower Comparator RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
| MAX987ESA+T | 功能描述:校验器 IC Single uPower Comparator RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
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