MCP6V27 datasheet(19/46 Pages) MICROCHIP

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DS25007A-page 19

MCP6V27

4.0

APPLICATIONS

The MCP6V27 auto-zeroed op amp is manufactured

using Microchip’s state of the art CMOS process. It is

designed for low cost, low power and high precision

applications. Its low supply voltage, low quiescent cur-

rent and wide bandwidth makes the MCP6V27 device

ideal for battery-powered applications.

4.1

Overview of Auto-Zeroing

Operation

Figure 4-1 shows a simplified diagram of the MCP6V27

auto-zeroed op amp. This will be used to explain how

the DC voltage errors are reduced in this architecture.

FIGURE 4-1:

Simplified Auto-Zeroed Op Amp Functional Diagram.

4.1.1

BUILDING BLOCKS

The Null Amplifier and Main Amplifier are designed for

high gain and accuracy using a differential topology.

They have a main input pair (+ and - pins at their top

left) used for the signal. They have an auxiliary input

pair (+ and - pins at their bottom left) used for correcting

the offset voltages. Both input pairs are added together

internally. The capacitors at the auxiliary inputs (CFW

and CH) hold the corrected values during normal

operation.

The Output Buffer is designed to drive external loads at

the VOUT pin. It also produces a single ended output

voltage (VREF is an internal reference voltage).

All of these switches are make-before-break in order to

minimize glitch-induced errors. They are driven by two

clock phases (

φ1 and φ2) that select between normal

mode and auto-zeroing mode.

The clock is derived from an internal R-C oscillator

running at a rate of fOSC1 = 850 kHz. The oscillator’s

output is divided down to the desired rate.

The internal POR ensures the part starts up in a known

good state. It also provides protection against power

supply brown-out events.

The Digital Control circuitry takes care of all of the

housekeeping details of the switching operation. It also

takes care of POR events.

VIN+

VIN–

Main

Output

VOUT

VREF

Amp.

Buffer

Null

Amp.

Null

Input

φ1

Switches

Null

Correct

φ2

Switches

Null

Output

Switches

CFW

POR

Digital

Control

Oscillator

φ1

φ2

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