MCP6141-ESLASHMS datasheet(16/38 Pages) MICROCHIP

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MCP6141/2/3/4

DS21668D-page 16

4.2

Rail-to-Rail Output

There are two specifications that describe the output

swing capability of the MCP6141/2/3/4 family of op

amps. The first specification (Maximum Output Voltage

Swing) defines the absolute maximum swing that can

be achieved under the specified load condition. Thus,

the output voltage swings to within 10 mV of either

supply rail with a 50 k

Ω load to VDD/2. Figure 2-10

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 Range. This specification defines the

maximum output swing that can be achieved while the

amplifier still operates in its linear region. To verify

linear operation in this range, the large signal DC

Open-Loop Gain (AOL) is measured at points inside the

supply rails. The measurement must meet the specified

AOL condition in the specification table.

4.3

Output Loads and Battery Life

The MCP6141/2/3/4 op amp family has outstanding

quiescent current, which supports battery-powered

applications. There is minimal quiescent current

glitching when Chip Select (CS) is raised or lowered.

This prevents excessive current draw, and reduced

battery life, when the part is turned off or on.

Heavy resistive loads at the output can cause

excessive battery drain. Driving a DC voltage of 2.5V

across a 100 k

Ω load resistor will cause the supply

current to increase by 25 µA, depleting the battery 43

times as fast as IQ (0.6 µA, typical) alone.

High frequency signals (fast edge rate) across

capacitive loads will also significantly increase supply

current. For instance, a 0.1 µF capacitor at the output

presents an AC impedance of 15.9 k

Ω (1/2πfC) to a

100 Hz sinewave. It can be shown that the average

power drawn from the battery by a 5.0 VP-P sinewave

(1.77 Vrms), under these conditions, is:

EQUATION 4-1:

This will drain the battery 18 times as fast as IQ alone.

4.4

Stability

4.4.1

NOISE GAIN

The MCP6141/2/3/4 op amp family is designed to give

high bandwidth and slew rate for circuits with high noise

gain (GN) or signal gain. Low gain applications should

be realized using the MCP6041/2/3/4 op amp family;

this simplifies design and implementation issues.

Noise gain is defined to be the gain from a voltage

source at the non-inverting input to the output when all

other voltage sources are zeroed (shorted out). Noise

gain is independent of signal gain and depends only on

components in the feedback loop. The amplifier circuits

in Figure 4-3 and Figure 4-4 have their noise gain

calculated as follows:

EQUATION 4-2:

In order for the amplifiers to be stable, the noise gain

should meet the specified minimum noise gain. Note

that a noise gain of GN = +10 V/V corresponds to a

non-inverting signal gain of G = +10 V/V, or to an

inverting signal gain of G = -9 V/V.

FIGURE 4-3:

Noise Gain for Non-inverting

Gain Configuration.

FIGURE 4-4:

Noise Gain for Inverting

Gain Configuration.

PSupply = (VDD - VSS) (IQ + VL(p-p) f CL )

= (5V)(0.6 µA + 5.0Vp-p · 100Hz · 0.1µF)

= 3.0 µW + 50 µW

-------

10 V/V

≥

VIN

MCP614X

RIN

VOUT

MCP614X

RIN

VOUT

VIN

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