MCP616 datasheet(12/30 Pages) MICROCHIP

12 / 30 page

MCP616/7/8/9

DS21613B-page 12

4.0

APPLICATIONS INFORMATION

The MCP616/7/8/9 family of op amps is manufactured

using Microchip’s state-of-the-art CMOS process,

which includes PNP transistors. These op amps are

unity-gain stable and suitable for a wide range of

general purpose applications.

4.1

Inputs

The MCP616/7/8/9 op amps are designed to prevent

phase reversal when the input pins exceed the supply

voltages.

Figure 2-33

shows

the

input

voltage

exceeding the supply voltage without any phase rever-

sal.

The inputs of the MCP616/7/8/9 op amps connect to a

differential PNP input stage. The Common Mode Input

Voltage Range (VCMR) includes ground in single-

supply systems (VSS), but does not include VDD. This

means that the amplifier input behaves linearly as long

as the Common Mode Input Voltage (VCM) is kept

within the specified limits (VSS to VDD – 0.9V at +25°C).

Input voltages that exceed the Absolute Maximum

Voltage Range (VSS – 0.3V to VDD + 0.3V) can cause

excessive current to flow into or out of the input pins.

Current beyond ±2 mA can cause reliability problems.

Applications that exceed this rating must be externally

limited with a resistor, as shown in Figure 4-1.

FIGURE 4-1:

Input Current-Limiting

Resistor (RIN).

4.2

DC Offsets

The MCP616/7/8/9 family of op amps have a PNP input

differential pair that gives good DC performance. They

have very low input offset voltage (±150 µV, max.) at

TA = +25°C, with a typical bias current of -15 nA

(sourced out of the inputs).

There must be a DC path to ground (or power supply)

from both inputs, or the op amp will not bias properly.

The DC resistances seen by the op amp inputs (R1||R2

and R4||R5 in Figure 4-2) need to be equal and less

than 100 k

Ω, to minimize the total DC offset.

FIGURE 4-2:

Example Circuit for

Calculating DC Offset.

To calculate the DC bias point and DC offset, convert

the circuit to its DC equivalent:

• Replace capacitors with open circuits

• Replace inductors with short circuits

• Replace AC voltage sources with short circuits

• Replace AC current sources with open circuits

• Convert DC sources and resistances into their

Thevenin equivalent form

The DC equivalent circuit for Figure 4-2 is shown in

Figure 4-3.

FIGURE 4-3:

Equivalent DC Circuit.

Maximum expected V

() V

–

2 mA

------------------------------------------------------------------------------

≥

Minimum expected V

()

–

2 mA

---------------------------------------------------------------------------

≥

VIN

MCP61X

RIN

VOUT

MCP61X

VOUT

MCP61X

VOUT

VEQ

REQ

------------------

⋅

4 || R5

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