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ADS7864 Datasheet, PDF (9/16 Pages) Burr-Brown (TI) – 500kHz, 12-Bit, 6-Channel Simultaneous Sampling ANALOG-TO-DIGITAL CONVERTER | |||
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CM +VREF
+IN
+VREF
CM Voltage
âIN = CM Voltage
âVREF
CM âVREF
t
Single-Ended Inputs
CM +1/2VREF
+IN
+VREF
CM Voltage
âVREF
âIN
CM â1/2VREF
t
Differential Inputs
(IN+) + (INâ)
NOTES: Common-Mode Voltage (Differential Mode) =
, Common-Mode Voltage (Single-Ended Mode) = INâ.
2
The maximum differential voltage between +IN and âIN of the ADS7864 is VREF. See Figures 3 and 4 for a further
explanation of the common voltage range for single-ended and differential inputs.
FIGURE 2. Using the ADS7864 in the Single-Ended and Differential Input Modes.
5
4.1
4
VCC = 5V
3
Single-Ended Input
2.7
2.3
2
1
0.9
0
5
4.7
4
3
Differential Input
2
1
0.3
0
VCC = 5V
4.05
0.90
â1
1.2
2.6
1.0
1.5
2.0
2.5
3.0
VREF (V)
FIGURE 3. Single-Ended Input: Common-Mode Voltage
Range vs VREF.
In each case, care should be taken to ensure that the output
impedance of the sources driving the +IN and âIN inputs are
matched. Otherwise, this may result in offset error, which
will change with both temperature and input voltage.
The input current on the analog inputs depend on a number
of factors: sample rate, input voltage, and source impedance.
Essentially, the current into the ADS7864 charges the inter-
nal capacitor array during the sampling period. After this
â1
1.2
2.6
1.0
1.5
2.0
2.5
3.0
VREF (V)
FIGURE 4. Differential Input: Common-Mode Voltage
Range vs VREF.
capacitance has been fully charged, there is no further input
current. The source of the analog input voltage must be able
to charge the input capacitance (15pF) to a 12-bit settling
level within 2 clock cycles. When the converter goes into the
hold mode, the input impedance is greater than 1Gâ¦.
Care must be taken regarding the absolute analog input
voltage. The +IN and âIN inputs should always remain
within the range of GND â 300mV to VDD + 300mV.
®
9
ADS7864
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