MCP6401 datasheet(15/28 Pages) MICROCHIP

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DS22229A-page 15

MCP6401/1R/1U

4.6

Application Circuits

4.6.1

PRECISION HALF-WAVE

RECTIFIER

The precision half-wave rectifier, which is also known

as a super diode, is a configuration obtained with an

operational amplifier in order to have a circuit behaving

like an ideal diode and rectifier. It effectively cancels the

forward voltage drop of the diode so that very low level

signals can still be rectified with minimal error. This can

be useful for high-precision signal processing. The

MCP6401/1R/1U op amps have high input impedance,

low input bias current and rail-to-rail input/output, which

makes this device suitable for precision rectifier

applications.

Figure 4-6 shows a precision half-wave rectifier and its

transfer characteristic. The rectifier’s input impedance

is determined by the input resistor R1. To avoid loading

effect, it must be driven from a low impedance source.

When VIN is greater than zero, D1 is OFF and D2 is ON,

VOUT is zero. When VIN is less than zero, D1 is ON and

D2 is OFF, and VOUT is the VIN with an amplification of

-R2/R1.

The rectifier circuit shown in Figure 4-6 has the benefit

that the op amp never goes in saturation, so the only

thing

affecting

its

frequency

response

the

amplification and the gain bandwidth product.

FIGURE 4-6:

Precision Half-Wave

Rectifier.

4.6.2

BATTERY CURRENT SENSING

The MCP6401/1R/1U op amps’ Common Mode Input

Range, which goes 0.3V beyond both supply rails,

supports their use in high side and low side battery

current sensing applications. The low quiescent current

(45 µA, typical) helps prolong battery life, and the

rail-to-rail output supports detection of low currents.

Figure 4-7 shows a high side battery current sensor

circuit. The 10

Ω resistor is sized to minimize power

losses. The battery current (IDD) through the 10Ω

resistor causes its top terminal to be more negative

than the bottom terminal. This keeps the common

mode input voltage of the op amp below VDD, which is

within its allowed range. The output of the op amp will

also be below VDD, which is within its Maximum Output

Voltage Swing specification.

FIGURE 4-7:

Supply Current Sensing.

4.6.3

INSTRUMENTATION AMPLIFIER

The MCP6401/1R/1U op amps are well suited for

conditioning

sensor

signals

battery-powered

applications.

Figure 4-8

shows

two

amp

instrumentation amplifier, using the MCP6401, that

works well for applications requiring rejection of

common mode noise at higher gains. The reference

voltage (VREF) is supplied by a low impedance source.

In single supply applications, VREF is typically VDD/2.

FIGURE 4-8:

Two Op Amp

Instrumentation Amplifier.

VOUT

VIN

VOUT

VIN

-R2/R1

Transfer Characteristic

Precision Half-Wave Rectifier

MCP6401

VDD

IDD

100 k

1.8V

VOUT

6.0V

OUT

–

10 V/V

() 10

()

⋅

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

To load

MCP6401

OUT

–

() 1

------

---------

⎝⎠

⎛⎞

REF

VREF R1

VOUT

MCP6401

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