Data Sheet
AD8226
Rev. C | Page 23 of 28
APPLICATIONS INFORMATION
DIFFERENTIAL DRIVE
+IN
–IN
REF
AD8226
VBIAS
R
+
–
OP AMP
+OUT
–OUT
07036-
009
R
RECOMMENDED OP AMPS: AD8515, AD8641, AD820.
RECOMMENDED R V
ALUES: 5k to 20k.
Figure 64. Differential Output Using an Op Amp
Figure 64 shows how to configure the AD8226 for differ-
ential output.
The differential output is set by the following equation:
VDIFF_OUT = VOUT+ VOUT = Gain × (VIN+ VIN)
The common-mode output is set by the following equation:
VCM_OUT = (VOUT+ VOUT)/2= VBIAS
The advantage of this circuit is that the dc differential accuracy
depends on the AD8226, not on the op amp or the resistors. In
addition, this circuit takes advantage of the precise control that the
AD8226 has of its output voltage relative to the reference voltage.
Although the dc performance and resistor matching of the op amp
affect the dc common-mode output accuracy, such errors are
likely to be rejected by the next device in the signal chain and
therefore typically have little effect on overall system accuracy.
Tips for Best Differential Output Performance
For best ac performance, an op amp with at least a 2 MHz gain
bandwidth and a 1 V/s slew rate is recommended. Good choices
Keep trace lengths from the resistors to the inverting terminal
of the op amp as short as possible. Excessive capacitance at this
node can cause the circuit to be unstable. If capacitance cannot
be avoided, use lower value resistors.
For best linearity and ac performance, a minimum positive
supply voltage (+VS) is required. Table 9 shows the minimum supply voltage required for optimum performance. In this mode,
VCM_MAX indicates the maximum common-mode voltage expected
at the input of the AD8226.
Table 9. Minimum Positive Supply Voltage
Temperature
Equation
Less than 10°C
+V
S > (VCM_MAX + VBIAS)/2 + 1.4 V
10°C to 25°C
+V
S > (VCM_MAX + VBIAS)/2 + 1.25 V
More than 25°C
+V
S > (VCM_MAX + VBIAS)/2 + 1.1 V