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5962-9201601MEA 参数 Datasheet PDF下载

5962-9201601MEA图片预览
型号: 5962-9201601MEA
PDF下载: 下载PDF文件 查看货源
内容描述: [16-Bit Current-Steering DAC with Voltage Reference]
分类和应用: 信息通信管理转换器
文件页数/大小: 8 页 / 308 K
品牌: ADI [ ADI ]
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Analog Circuit Considerations–AD766  
The digital ground pin returns ground current from the digital  
logic portions of the AD766 circuitry. This pin should be con-  
nected to the digital common point in the system.  
For applications requiring broader bandwidths and/or even  
lower noise than that afforded by the AD766’s internal op amp,  
an external op amp can easily by used in its place. IOUT (Pin 13)  
drives the negative (inverting) input terminal of the external op  
amp, and its external voltage output is connected to the feed-  
back resistor pin, RF (Pin 10). To insure that the AD766’s un-  
used internal op amp remains in a closed-loop configuration,  
As illustrated in Figure 5, the analog and digital grounds should  
be connected together at one point in the system.  
VOUT (Pin 9) should be tied to the summing junction pin, SJ  
(Pin 11).  
As an example, Figure 3 shows the AD766 using the AD744 op  
amp as an external current-to-voltage converter. In this invert-  
ing configuration, the AD744 will provide the same ±3 V out-  
put as the internal op amp would have. Other recommended  
amplifiers include the AD845 and AD846. Note that a single  
pole of low-pass filtering could also be attained with this circuit  
simply by adding a capacitor in parallel with the feedback resis-  
tor as just shown in Figure 1.  
Figure 5. Recommended Circuit Schematic  
POWER SUPPLIES AND DECOUPLING  
The AD766 has four power supply input pins. ±VS provide the  
supply voltages to operate the linear portions of the DAC in-  
cluding the voltage reference, output amplifier and control am-  
plifier. The ±VS supplies are designed to operate from ±5 V to  
±12 V.  
The ±VL supplies operate the digital portions of the chip, in-  
cluding the input shift register and the input latching circuitry.  
The ±VL supplies are also designed to operate from ±5 V to  
±12 V. To assure freedom from latch-up, –VL should never go  
more negative than –VS.  
Figure 3. External Op Amp Connections  
Special restrictions on power supplies apply to extended tem-  
perature range versions of the AD766 that do not apply to the  
commercial AD766J. First, supplies must be symmetric. That is,  
+VS = ͉–VS͉ and +VL = ͉–VL͉. Each supply must independently  
meet this equality within ±5%. Since we require that –VS –VL  
to guarantee latch-up immunity, this symmetry principle implies  
that the positive analog supply must be greater than or equal to  
the positive digital supply, i.e., VS –VL for extended-temper-  
ature range parts. In other words, the digital supply range must  
be inside the analog supply range. Second, the internal op amp’s  
performance in generating voltage outputs is only guaranteed if  
+VS 7 V (and –VS –7 V, by the symmetry principle). These  
constraints do not apply to the AD766J.  
Residual DAC differential linearity error around midscale can  
be externally trimmed out, improving THD beyond the  
AD766’s guaranteed tested specifications. This error is most  
significant with low-amplitude signals because the ratio of the  
midscale linearity error to the signal amplitude is greatest in this  
case, thereby increasing THD. The MSB adjust circuitry shown  
in Figure 4 can be used for improving THD with low-level sig-  
nals. Otherwise, the AD766 will operate to its specifications  
with MSB ADJ (Pin 14) and TRIM (Pin 15) unconnected.  
Decoupling capacitors should be used on all power supply pins.  
Furthermore, good engineering practice suggests that these ca-  
pacitors be placed as close as possible to the package pins as  
well as the common points. The logic supplies, ±VL, should be  
decoupled to digital common; and the analog supplies, ±VS,  
should be decoupled to analog common.  
Figure 4. Optional MSB Adjustment Circuit  
ANALOG CIRCUIT CONSIDERATIONS  
GROUNDING RECOMMENDATIONS  
The AD766 has two ground pins, designated AGND (analog  
ground) and DGND (digital ground). The analog ground pin is  
the “high-quality” ground reference point for the device. The  
analog ground pin should be connected to the analog common  
point in the system. The output load should also be connected  
to that same point.  
The use of four separate power supplies will reduce feedthrough  
from the digital portion of the system to the linear portions of  
the system, thus contributing to the performance as tested.  
However, four separate voltage supplies are not necessary for  
good circuit performance. For example, Figure 6 illustrates a  
REV. A  
–5–