MCP6021 datasheet(19/42 Pages) MICROCHIP

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DS21685D-page 19

MCP6021/1R/2/3/4

4.6

MCP6021 and MCP6023 Reference

Voltage

The single op amps (MCP6021 and MCP6023), not in

the SOT-23-5 package, have an internal mid-supply

reference voltage connected to the VREF pin (see

Figure 4-7). The MCP6021 has CS internally tied to

VSS, which always keeps the op amp on and always

provides a mid-supply reference. With the MCP6023,

taking the CS pin high conserves power by shutting

down both the op amp and the VREF circuitry. Taking

the CS pin low turns on the op amp and VREF circuitry.

FIGURE 4-7:

Simplified internal VREF

circuit (MCP6021 and MCP6023 only).

See Figure 4-8 for a non-inverting gain circuit using the

internal

mid-supply

reference.

The

DC-blocking

capacitor (CB) also reduces noise by coupling the op

amp input to the source.

FIGURE 4-8:

Non-inverting gain circuit

using VREF (MCP6021 and MCP6023 only).

To use the internal mid-supply reference for an

inverting gain circuit, connect the VREF pin to the

non-inverting input, as shown in Figure 4-9. The

capacitor CB helps reduce power supply noise on the

output.

FIGURE 4-9:

Inverting gain circuit using

VREF (MCP6021 and MCP6023 only).

If you don’t need the mid-supply reference, leave the

VREF pin open.

4.7

Supply Bypass

With this family of operational amplifiers, the power

supply pin (VDD for single supply) should have a local

bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm

for good, high-frequency performance. It also needs a

bulk capacitor (i.e., 1 µF or larger) within 100 mm to

provide large, slow currents. This bulk capacitor can be

shared with nearby analog parts.

4.8

Unused Op Amps

An unused op amp in a quad package (MCP6024)

should be configured as shown in Figure 4-10. These

circuits prevent the output from toggling and causing

crosstalk. Circuits 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; 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 4-10:

Unused Op Amps.

VDD

VSS

VREF

50 k

(CS tied internally to VSS for MCP6021)

VIN

VOUT

VREF

VIN

VOUT

VREF

VDD

¼ MCP6024 (A)

¼ MCP6024 (B)

VDD

VREF

REF

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