Datasheet
Table Of Contents
- Package Types
- Typical Application
- 1.0 Electrical Characteristics
- 2.0 Typical Performance Curves
- Figure 2-1: Input Offset Voltage
- Figure 2-2: Input Offset Voltage Drift
- Figure 2-3: Input Offset Voltage vs. Common Mode Input Voltage
- Figure 2-4: Input Offset Voltage vs. Common Mode Input Voltage
- Figure 2-5: Input Offset Voltage vs. Output Voltage
- Figure 2-6: Input Offset Voltage vs. Power Supply Voltage
- FIGURE 2-7: Input Noise Voltage Density vs. Frequency.
- FIGURE 2-8: Input Noise Voltage Density vs. Common Mode Input Voltage.
- FIGURE 2-9: CMRR, PSRR vs. Frequency.
- FIGURE 2-10: CMRR, PSRR vs. Ambient Temperature.
- FIGURE 2-11: Input Bias, Offset Currents vs. Ambient Temperature.
- FIGURE 2-12: Input Bias Current vs. Common Mode Input Voltage.
- FIGURE 2-13: Quiescent Current vs. Ambient Temperature.
- FIGURE 2-14: Quiescent Current vs. Common Mode Input Voltage.
- FIGURE 2-15: Quiescent Current vs. Common Mode Input Voltage.
- FIGURE 2-16: Quiescent Current vs. Power Supply Voltage.
- FIGURE 2-17: Open-Loop Gain, Phase vs. Frequency.
- FIGURE 2-18: DC Open-Loop Gain vs. Ambient Temperature.
- FIGURE 2-19: Gain Bandwidth Product, Phase Margin vs. Ambient Temperature.
- FIGURE 2-20: Gain Bandwidth Product, Phase Margin vs. Ambient Temperature.
- FIGURE 2-21: Output Short Circuit Current vs. Power Supply Voltage.
- FIGURE 2-22: Output Voltage Swing vs. Frequency.
- FIGURE 2-23: Output Voltage Headroom vs. Output Current.
- FIGURE 2-24: Output Voltage Headroom vs. Output Current.
- FIGURE 2-25: Output Voltage Headroom vs. Ambient Temperature.
- FIGURE 2-26: Output Voltage Headroom vs. Ambient Temperature.
- FIGURE 2-27: Slew Rate vs. Ambient Temperature.
- FIGURE 2-28: Small Signal Non-Inverting Pulse Response.
- FIGURE 2-29: Small Signal Inverting Pulse Response.
- FIGURE 2-30: Large Signal Non-Inverting Pulse Response.
- FIGURE 2-31: Large Signal Inverting Pulse Response.
- FIGURE 2-32: The MCP6491/2/4 Shows No Phase Reversal.
- FIGURE 2-33: Closed Loop Output Impedance vs. Frequency.
- FIGURE 2-34: Measured Input Current vs. Input Voltage (below VSS).
- FIGURE 2-35: Channel-to-Channel Separation vs. Frequency (MCP6492/4 only).
- 3.0 Pin Descriptions
- 4.0 Application Information
- 5.0 Design Aids
- 6.0 Packaging Information
- Appendix A: Revision History
- Product Identification System
- Trademarks
- Worldwide Sales and Service
2012-2013 Microchip Technology Inc. DS20002321C-page 19
MCP6491/2/4
4.7.3 PH ELECTRODE AMPLIFIER
The MCP6491/2/4 op amps can be used for sensing
applications where the sensor has high output
impedance, such as a pH electrode sensor; its output
impedance is in the range of 1 M to 1G. The key op
amp specifications for these kinds of applications are
low-input bias current and high-input impedance.
A typical sensing circuit is shown in Figure 4-12, it is
implemented with a non-inverting amplifier which has a
gain of 1+R
2
/R
1
. The input voltage error due to input
bias current is equal to I
B
*R
OUT
, which is amplified by
1+R
2
/R
1
at the output. To minimize the voltage error
and get the V
OUT
with better accuracy, the I
B
must be
small enough.
FIGURE 4-12: pH Electrode Amplifier.
V
OUT
R
1
R
2
V
IN
+
–
MCP6491
pH electrode
V
SEN
V
SEN
is the sensed voltage by pH electrode
R
OUT
is the pH electrode’s output impedance
+
–
R
OUT