+IN
CM +VREF
+VREF
CM Voltage
–IN = CM Voltage
–VREF
t
CM –VREF
Single-Ended Inputs
+IN
+VREF
CM +1/2VREF
CM Voltage
–VREF
–IN
t
CM –1/2VREF
Differential Inputs
(IN+) + (IN–)
NOTES: Common-Mode Voltage (Differential Mode) =
Common-Mode Voltage (Single-Ended Mode) = IN–.
2
The maximum differential voltage between +IN and –IN of the ADS7862 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 ADS7862 in the Single-Ended and Differential Input Modes.
5
4
5
4
VCC = 5V
4.7
VCC = 5V
4.1
4.05
3
3
2.7
2.3
Single-Ended Input
Differential Input
2
2
0.90
1
1
0.9
0.3
0
0
–1
–1
1.2
2.52.6
3.0
1.2
1.0
1.5
2.0
2.52.6
3.0
1.0
1.5
2.0
VREF (V)
VREF (V)
FIGURE 3. Single-Ended Input: Common-Mode Voltage
Range vs VREF
FIGURE 4. Differential 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 –IN inputs are
matched. Otherwise, this may result in offset error, which
will change with both temperature and input voltage.
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 1GΩ.
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 ADS7862 charges the inter-
nal capacitor array during the sampling period. After this
Care must be taken regarding the absolute analog input
voltage. The +IN input should always remain within the
range of GND – 300mV to VDD + 0.3V.
®
ADS7862
9
BB [ BURR-BROWN CORPORATION ]
