MCP601 datasheet(11/28 Pages) MICROCHIP

11 / 28 page

 2004 Microchip Technology Inc.

DS21314F-page 11

MCP601/2/3/4

3.0

APPLICATIONS INFORMATION

The MCP601/2/3/4 family of op amps are fabricated on

Microchip’s state-of-the-art CMOS process. They are

unity-gain stable and suitable for a wide range of

general purpose applications.

3.1

Input

The MCP601/2/3/4 amplifier family is designed to not

exhibit phase reversal when the input pins exceed the

supply rails. Figure 2-33 shows an input voltage that

exceeds both supplies with no resulting phase

inversion.

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 VCMR

limits (VSS – 0.3V to VDD – 1.2V at +25°C).

Input voltages that exceed the input voltage range

(VSS – 0.3V to VDD – 1.2V at +25°C) can cause exces-

sive current to flow into or out of the input pins. Current

beyond ±2 mA may cause reliability problems.

Applications that exceed this rating must externally

limit the input current with a resistor (RIN), as shown in

Figure 3-1.

FIGURE 3-1:

RIN limits the current flow

into an input pin.

3.2

Rail-to-Rail Output

There are two specifications that describe the output

swing capability of the MCP601/2/3/4 family of op amps.

The first specification (Maximum Output Voltage Swing)

defines the absolute maximum swing that can be

achieved under the specified load conditions. For

instance, the output voltage swings to within 15 mV of

the negative rail with a 25 k

Ω load to VDD/2. Figure 2-33

shows how the output voltage is limited when the input

goes beyond the linear region of operation.

The second specification that describes the output

swing capability of these amplifiers is the Linear Output

Voltage Swing. This specification defines the maximum

output swing that can be achieved while the amplifier is

still operating in its linear region. To verify linear

operation in this range, the large signal (DC Open-Loop

Gain (AOL)) is measured at points 100 mV inside the

supply rails. The measurement must exceed the

specified gains in the specification table.

3.3

MCP603 Chip Select (CS)

The MCP603 is a single amplifier with Chip Select

(CS). When CS is pulled high, the supply current drops

to -0.7 µA (typ.), which is pulled through the CS pin to

VSS. When this happens, the amplifier output is put into

a high-impedance state. Pulling CS low enables the

amplifier and, if the CS pin is left floating, the amplifier

may not operate properly. Figure 1-1 is the Chip Select

timing diagram and shows the output voltage, supply

currents and CS current in response to a CS pulse.

Figure 2-27 shows the measured output voltage

response to a CS pulse.

3.4

Capacitive Loads

Driving large capacitive loads can cause stability

problems for voltage feedback op amps. As the load

capacitance increases, the feedback loop’s phase

margin decreases and the closed-loop bandwidth is

reduced. This produces gain peaking in the frequency

response with overshoot and ringing in the step

response.

When driving large capacitive loads with these op

amps (e.g., > 40 pF when G = +1), a small series

resistor at the output (RISO in Figure 3-2) improves the

feedback loop’s phase margin (stability) by making the

output load resistive at higher frequencies. The

bandwidth will be generally lower than the bandwidth

with no capacitive load.

FIGURE 3-2:

Output resistor RISO

stabilizes large capacitive loads.

Figure 3-3 gives recommended RISO values for

different capacitive loads and gains. The x-axis is the

normalized load capacitance (CL/GN) in order to make

it easier to interpret the plot for arbitrary gains. GN is the

circuit’s noise gain. For non-inverting gains, GN and the

gain are equal. For inverting gains, GN = 1 + |Gain|

(e.g., -1 V/V gives GN = +2 V/V).

MCP60X

RIN

VIN

–

RIN

maximum expected VIN

() VDD

–

2 mA

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

≥

RIN

VSS

minimum expected VIN

()

–

2 mA

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

≥

MCP60X

RISO

VOUT

–

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