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BUF634U-2K5E4 参数 Datasheet PDF下载

BUF634U-2K5E4图片预览
型号: BUF634U-2K5E4
PDF下载: 下载PDF文件 查看货源
内容描述: 250mA高速缓冲器 [250mA HIGH-SPEED BUFFER]
分类和应用:
文件页数/大小: 20 页 / 851 K
品牌: BB [ BURR-BROWN CORPORATION ]
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OUTPUT CURRENT  
APPLICATION INFORMATION  
The BUF634 can deliver up to ±250mA continuous output  
current. Internal circuitry limits output current to approxi-  
mately ±350mA—see typical performance curve “Short  
Circuit Current vs Temperature”. For many applications,  
however, the continuous output current will be limited by  
thermal effects.  
Figure 1 is a simplified circuit diagram of the BUF634  
showing its open-loop complementary follower design.  
V+  
The output voltage swing capability varies with junction  
temperature and output current—see typical curves “Output  
Voltage Swing vs Output Current.” Although all four pack-  
age types are tested for the same output performance using  
a high speed test, the higher junction temperatures with the  
DIP and SO-8 package types will often provide less output  
voltage swing. Junction temperature is reduced in the DDPAK  
surface-mount power package because it is soldered directly  
to the circuit board. The TO-220 package used with a good  
heat sink further reduces junction temperature, allowing  
maximum possible output swing.  
Thermal  
Shutdown  
200  
VIN  
VO  
(1)  
I1  
THERMAL PROTECTION  
150Ω  
4kΩ  
Power dissipated in the BUF634 will cause the junction  
temperature to rise. A thermal protection circuit in the  
BUF634 will disable the output when the junction tempera-  
ture reaches approximately 175°C. When the thermal pro-  
tection is activated, the output stage is disabled, allowing the  
device to cool. Quiescent current is approximately 6mA  
during thermal shutdown. When the junction temperature  
cools to approximately 165°C the output circuitry is again  
enabled. This can cause the protection circuit to cycle on and  
off with a period ranging from a fraction of a second to  
several minutes or more, depending on package type, signal,  
load and thermal environment.  
BW  
V–  
Signal path indicated in bold.  
Note: (1) Stage currents are set by I1.  
FIGURE 1. Simplified Circuit Diagram.  
Figure 2 shows the BUF634 connected as an open-loop  
buffer. The source impedance and optional input resistor,  
RS, influence frequency response—see typical curves. Power  
supplies should be bypassed with capacitors connected close  
to the device pins. Capacitor values as low as 0.1µF will  
assure stable operation in most applications, but high output  
current and fast output slewing can demand large current  
transients from the power supplies. Solid tantalum 10µF  
capacitors are recommended.  
The thermal protection circuit is designed to prevent damage  
during abnormal conditions. Any tendency to activate the  
thermal protection circuit during normal operation is a sign  
of an inadequate heat sink or excessive power dissipation for  
the package type.  
TO-220 package provides the best thermal performance.  
When the TO-220 is used with a properly sized heat sink,  
output is not limited by thermal performance. See Applica-  
tion Bulletin AB-037 for details on heat sink calculations.  
The DDPAK also has excellent thermal characteristics. Its  
mounting tab should be soldered to a circuit board copper  
area for good heat dissipation. Figure 3 shows typical  
thermal resistance from junction to ambient as a function of  
the copper area. The mounting tab of the TO-220 and  
DDPAK packages is electrically connected to the V– power  
supply.  
High frequency open-loop applications may benefit from  
special bypassing and layout considerations—see “High  
Frequency Applications” at end of applications discussion.  
V+  
10µF  
DIP/SO-8  
Pinout shown  
7
RS  
VIN  
3
6
The DIP and SO-8 surface-mount packages are excellent for  
applications requiring high output current with low average  
power dissipation. To achieve the best possible thermal  
performance with the DIP or SO-8 packages, solder the  
device directly to a circuit board. Since much of the heat is  
dissipated by conduction through the package pins, sockets  
will degrade thermal performance. Use wide circuit board  
traces on all the device pins, including pins that are not  
connected. With the DIP package, use traces on both sides  
of the printed circuit board if possible.  
VO  
BUF634  
1
RL  
4
10µF  
Optional connection for  
wide bandwidth — see text.  
V–  
FIGURE 2. Buffer Connections.  
®
7
BUF634