MCP6C04 datasheet(34/54 Pages) MICROCHIP

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MCP6C04

DS20006179A-page 34

 2019 Microchip Technology Inc.

4.2

Overview of Zero-Drift Operation

Figure 4-4 shows a diagram of the MCP6C04; It explains how slow voltage errors at the input are reduced in this archi-

tecture (much better VOS, TC1 TC2, CMRR, CMRR2, PSRR and 1/f noise).

FIGURE 4-4:

MCP6C04 Block Diagram.

4.2.1

BUILDING BLOCKS

The Main Amplifiers (GM1 and GM2) are designed for

high gain and bandwidth, with a differential topology.

The main input pairs (+ and - pins at the top left) are for

the higher frequency portion of the input signal. The

auxiliary input pairs (+ and - pins at the bottom left) are

for the low frequency and high precision portion of the

input signal and correct the input offset voltage. Both

inputs are added together internally

The auxiliary amplifiers (GA1 and GA2), the chopper

input switches and the chopper output switches provide

a high DC gain to the input signal. DC errors are

modulated to higher frequencies and white noise to low

frequencies.

The low-pass filter reduces high-frequency content,

including harmonics of the chopping clock.

The output buffer (RM4) converts current to voltage,

drives the external load at VOUT and creates a negative

feedback loop through RF and RG. RF and RG help set

the differential gain.

The oscillator runs at fCLK = 50 kHz for the gains of 20

and 50, and at fCLK = 100 kHz for the gain of 100. fCLK

is divided by 2, to produce the chopping clock rate

(25 kHz and 50 kHz, respectively).

The internal LV POR (for VDD –VSS) starts the part in

a known good state, protecting against power supply

brown-outs. The internal HV POR (for VIP –VSS)

ensures protection of the low voltage circuitry, as well

as proper functioning.

4.2.2

CHOPPING ACTION

Figure 4-5 shows the amplifier connections for the first

phase of the Chopping Clock and Figure 4-6 shows

them for the second phase. The slow voltage errors

alternate in polarity, making the average error small.

FIGURE 4-5:

First Chopping Clock Phase;

Simplified Diagram.

VIP

VIM

GM1

GA1

Chopper

Input

Switches

Chopper

Output

Switches

Low-Pass

Filter

RM4

VOUT

VREF

GM2

GA2

Chopper

Input

Switches

Chopper

Output

Switches

Low-Pass

Filter

EMI

Filters

Clamps

EMI

Filter

VFG

VIP

VIM

GA1

Low-

Pass

Filter

VREF

VFG

GA2

Low-

Pass

Filter

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