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ADS8380
REFM
REFIN
REFOUT
AGND
0.1 mF
1 mF
ADS8380
REFM
REFIN
REFOUT
AGND
0.1 mF
1 mF
External
Reference
ADS8380
AGND
+VA
_
+
53 W
53 W
40 pF 40 pF
+IN
−IN
AGND
ANALOG INPUT
ADS8380
SLAS387A – NOVEMBER 2004 – REVISED DECEMBER 2004
PRINCIPLES OF OPERATION (continued)
Figure 48. ADS8380 Using Internal Reference
The REFIN pin is also internally buffered. This eliminates the need to put a high bandwidth buffer on the board
to drive the ADC reference and saves system area and power. When an external reference is used, the
reference must be of low noise, which may be achieved by the addition of bypass capacitors from the REFIN pin
to the REFM pin. See Figure 49 for operation of the ADS8380 with an external reference. REFM must be
connected to the analog ground plane.
Figure 49. ADS8380 Using External Reference
Figure 50. Simplified Analog Input
When the converter enters hold mode, the voltage difference between the +IN and –IN inputs is captured on the
internal capacitor array. The +IN input has a range of –0.2 V to (+V
REF
+ 0.2 V), whereas the –IN input has a
range of –0.2 V to +0.2 V. The input span (+IN – (–IN)) is limited from 0 V to V
REF
.
The input current on the analog inputs depends upon throughput and the frequency content of the analog input
21
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