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DAC900EG4 参数 Datasheet PDF下载

DAC900EG4图片预览
型号: DAC900EG4
PDF下载: 下载PDF文件 查看货源
内容描述: 10位, 165MSPS数位类比转换器 [10-Bit, 165MSPS DIGITAL-TO-ANALOG CONVERTER]
分类和应用: 转换器数模转换器光电二极管
文件页数/大小: 24 页 / 798 K
品牌: TI [ TEXAS INSTRUMENTS ]
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INTERNAL REFERENCE OPERATION  
The DC gain for this circuit is equal to feedback resistor RF.  
At high frequencies, the DAC output impedance (CD1, CD2)  
will produce a zero in the noise gain for the OPA2680 that  
may cause peaking in the closed-loop frequency response.  
CF is added across RF to compensate for this noise-gain  
peaking. To achieve a flat transimpedance frequency re-  
sponse, the pole in each feedback network should be set to:  
The DAC900 has an on-chip reference circuit that comprises  
a 1.24V bandgap reference and a control amplifier. Ground-  
ing pin 16, INT/EXT, enables the internal reference opera-  
tion. The full-scale output current, IOUTFS, of the DAC900 is  
determined by the reference voltage, VREF, and the value of  
resistor RSET. IOUTFS can be calculated by:  
IOUTFS = 32 • IREF = 32 • VREF / RSET  
(10)  
1
GBP  
=
(8)  
2πRFCF 4πRFCD  
As shown in Figure 7, the external resistor RSET connects to  
the FSA pin (Full-Scale Adjust). The reference control am-  
plifier operates as a V-to-I converter producing a reference  
current, IREF, which is determined by the ratio of VREF and  
RSET, as shown in Equation 10. The full-scale output current,  
IOUTFS, results from multiplying IREF by a fixed factor of 32.  
with GBP = Gain Bandwidth Product of OPA  
which will give a corner frequency f-3dB of approximately:  
GBP  
f3dB  
=
(9)  
2πRFCD  
+5V  
CCOMPEXT  
0.1µF  
The full-scale output voltage is defined by the product of  
IOUTFS • RF, and has a negative unipolar excursion. To  
improve on the ac performance of this circuit, adjustment of  
RF and/or IOUTFS should be considered. Further extensions of  
this application example may include adding a differential  
filter at the OPA2680’s output followed by a transformer, in  
order to convert to a single-ended signal.  
BW  
+VA  
DAC900  
VREF  
RSET  
IREF  
=
FSA  
Ref  
Control  
Amp  
Current  
Sources  
REFIN  
RSET  
2kΩ  
SINGLE-ENDED CONFIGURATION  
CCOMP  
400pF  
0.1µF  
Using a single load resistor connected to the one of the DAC  
outputs, a simple current-to-voltage conversion can be ac-  
complished. The circuit in Figure 6 shows a 50resistor  
connected to IOUT, providing the termination of the further  
connected 50cable. Therefore, with a nominal output  
current of 20mA, the DAC produces a total signal swing of  
0V to 0.5V into the 25load.  
INT/EXT  
+1.24V Ref.  
FIGURE 7. Internal Reference Configuration.  
Using the internal reference, a 2kresistor value results in a  
20mA full-scale output. Resistors with a tolerance of 1% or better  
should be considered. Selecting higher values, the converter  
output can be adjusted from 20mA down to 2mA. Operating the  
DAC900 at lower than 20mA output currents may be desirable  
for reasons of reducing the total power consumption, improving  
the distortion performance, or observing the output compliance  
voltage limitations for a given load condition.  
IOUTFS = 20mA  
VOUT = 0V to +0.5V  
IOUT  
DAC900  
IOUT  
50  
50Ω  
25Ω  
It is recommended to bypass the REFIN pin with a ceramic chip  
capacitor of 0.1µF or more. The control amplifier is internally  
compensated, and its small signal bandwidth is approximately  
1.3MHz. To improve the ac performance, an additional capacitor  
(CCOMPEXT) should be applied between the BW pin and the  
analog supply, +VA, as shown in Figure 7. Using a 0.1µF  
capacitor, the small-signal bandwidth and output impedance of  
the control amplifier is further diminished, reducing the noise that  
is fed into the current source array. This also helps shunting  
feedthrough signals more effectively, and improving the noise  
performance of the DAC900.  
FIGURE 6. Driving a Doubly-Terminated 50Cable Directly.  
Different load resistor values may be selected as long as the  
output compliance range is not exceeded. Additionally, the  
output current, IOUTFS, and the load resistor may be mutually  
adjusted to provide the desired output signal swing and  
performance.  
DAC900  
14  
SBAS093B