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 17
MCP6491/2/4
4.5 Unused Op Amps
An unused op amp in a quad package (MCP6494)
should be configured as shown in Figure 4-6. These
circuits prevent the output from toggling and causing
crosstalk. Circuit A sets the op amp at its minimum
noise gain. The resistor divider produces any desired
reference voltage within the output voltage range of the
op amp, and the op amp buffers that reference voltage.
Circuit B uses the minimum number of components
and operates as a comparator, but it may draw more
current.
FIGURE 4-6: Unused Op Amps.
4.6 PCB Surface Leakage
In applications where low-input bias current is critical,
PCB surface leakage effects need to be considered.
Surface leakage is caused by humidity, dust or other
contamination on the board. Under low-humidity
conditions, a typical resistance between nearby traces
is 10
12
. A 5V difference would cause 5 pA of current
to flow, which is greater than the MCP6491/2/4 family’s
bias current at +25°C (1 pA, typical).
The easiest way to reduce surface leakage is to use a
guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin.
An example of this type of layout is shown in
Figure 4-7.
FIGURE 4-7: Example Guard Ring Layout
for Inverting Gain.
1. Non-Inverting Gain and Unity-Gain Buffer:
a.Connect the non-inverting pin (V
IN
+) to the
input with a wire that does not touch the
PCB surface.
b.Connect the guard ring to the inverting input
pin (V
IN
–). This biases the guard ring to the
Common mode input voltage.
2. Inverting Gain and Transimpedance Gain
Amplifiers (convert current to voltage, such as
photo detectors):
a.Connect the guard ring to the non-inverting
input pin (V
IN
+). This biases the guard ring
to the same reference voltage as the op
amp (e.g., V
DD
/2 or ground).
b.Connect the inverting pin (V
IN
–) to the input
with a wire that does not touch the PCB
surface.
V
DD
V
DD
R
1
R
2
V
DD
V
REF
V
REF
V
DD
R
2
R
1
R
2
+
--------------------
=
¼ MCP6494 (A)
¼ MCP6494 (B)
Guard Ring V
IN
–V
IN
+ V
SS