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Application Information (Continued)
headphones are connected to the jack shown in Figure 8,
and internal pullup forces V
DD on the internal comparator’s
HPIN inputs. This changes the comparator’s output state
and enables the headphone function: it turns off Amp2B,
switches Amp2A’s input signal from an audio signal to the
V
DD/2 voltage present on pin 14, and mutes the bridge-
connected loads. Amp1A and Amp1B drive the headphones.
Figure 8 also shows the suggested headphone jack electri-
cal connections. The jack is designed to mate with a
threewire plug. The plug’s tip and ring should each carry
one of the two stereo output signals, whereas the sleeve
provides the return to Amp2A. A headphone jack with one
control pin contact is sufficient to drive the HPIN pin when
connecting headphones.
A switch can replace the headphone jack contact pin. When
a switch shorts the HPIN pin to V
DD, bridgeconnected
speakers are muted and Amp1A and Amp2A drive a pair of
headphones. When a switch shorts the HPIN pin to GND,
the LM4867 operates in bridge mode. If headphone drive is
not needed, short the HPIN pin to the OUTB pin.
Figure 7 shows an optional resistor connected between the
amplifier output that drives the headphone jack sleeve and
ground. This resistor provides a ground path that supressed
power supply hum. This hum may occur in applications such
as notebook computers in a shutdown condition and con-
nected to an external powered speaker. The resistor’s 100
value is a suggested starting point. Its final value must be
determined based on the tradeoff between the amount of
noise suppression that may be needed and minimizing the
additional current drawn by the resistor (25mA for a 100
resistor and a 5V supply).
ESD PROTECTION
As stated in the Absolute Maximum Ratings, pin 28 on the
MT and MH packages have a maximum ESD susceptibility
rating of 8000V. For higher ESD voltages, the addition of a
PCDN042 dual transil (from California Micro Devices), as
shown in Figure 7, will provide additional protection.
SINGLE-ENDED OUTPUT POWER PERFORMANCE
AND MEASUREMENT CONSIDERATIONS
The LM4867 delivers clean, low distortion SE output power
into loads that are greater than 10
. As an example, output
power for 16
and 32 loads are shown in the Typical
Performance Characteristic curves. For loads less than
10
, the LM4876 can typically supply 180mW of low distor-
tion power. However, when higher dissipation is desired in
loads less than 10
, a dramatic increase in THD+N may
occur. This is normal operation and does not indicate that
proper functionality has ceased. When a jump from moder-
ate to excessively high distortion is seen, simply reducing
the output voltage swing will restore the clean, low distortion
SE operation.
The dramatic jump in distortion for loads less than 10
occurs when current limiting circuitry activates. During SE
operation, AMP2A (refer to Figure 4) drives the headphone
sleeve. An on-board circuit monitors this amplifier’s output
current. The sudden increase in THD+N is caused by the
current limit circuitry forcing AMP2A into a highimpedance
output mode. When this occurs, the output waveform has
discontinuities that produce large amounts of distortion. It
has been observed that as the output power is steadily
increased, the distortion may jump from 5% to greater than
35%. Indeed, 10% THD+N may not actually be achievable.
USING THE SINGLEENDED OUTPUT FOR LINE
LEVEL APPLICATIONS
Some samples of the LM4867 may exhibit small amplitude,
high frequency oscillation when the SE output is connected
to a line-level input. This oscillation can be eliminated by
connecting a 5%, 300
resistor between Amp2A’s output pin
and each amplifier, AMP1A and AMP1B, output.
20001371
FIGURE 7. The PCDN042 provides additional ESD protection beyond the 8000V shown in the Absolute Maximum
Ratings for the AMP2A output
LM4867
www.national.com
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相关代理商/技术参数
LM4867MT 制造商:NSC 制造商全称:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function
LM4867MT NOPB 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 2-CH Stereo 1.5W Class-AB 20-Pin TSSOP Rail
LM4867MT/NOPB 功能描述:IC AMP AUDIO PWR 3W AB 20TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR)
LM4867MTE 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 2-CH Stereo 3W Class-AB 20-Pin TSSOP EP Rail
LM4867MTE/NOPB 功能描述:IC AMP AUDIO PWR 3W AB 20TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR)
LM4867MTEX 制造商:National Semiconductor Corporation 功能描述:Audio Amplifier Circuit, Dual, 20 Pin, Plastic, TSSOP
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