TC7116 datasheet(8/24 Pages) MICROCHIP

8 / 24 page

TC7116/A/TC7117/A

DS21457C-page 8

3.0

DETAILED DESCRIPTION

(All Pin Designations Refer to 40-Pin PDIP.)

3.1

Analog Section

Figure 3-1 shows the block diagram of the analog sec-

tion for the TC7116/TC7116A and TC7117/TC7117A.

Each measurement cycle is divided into three phases:

(1) Auto-Zero (AZ), (2) Signal Integrate (INT), and

(3) Reference Integrate (REF), or De-integrate (DE).

3.1.1

AUTO-ZERO PHASE

High and low inputs are disconnected from the pins and

internally shorted to analog common. The reference

capacitor is charged to the reference voltage. A feed-

back loop is closed around the system to charge the

auto-zero capacitor (CAZ) to compensate for offset volt-

ages in the buffer amplifier, integrator, and comparator.

Since the comparator is included in the loop, AZ

accuracy is limited only by system noise. The offset

referred to the input is less than 10

μV.

3.1.2

SIGNAL INTEGRATE PHASE

The auto-zero loop is opened, the internal short is

removed, and the internal high and low inputs are

connected to the external pins. The converter then inte-

grates the differential voltages between VIN+ and VIN-

for a fixed time. This differential voltage can be within a

wide Common mode range: 1V of either supply. How-

ever, if the input signal has no return with respect to the

converter power supply, VIN- can be tied to analog

common to establish the correct Common mode

voltage. At the end of this phase, the polarity of the

integrated signal is determined.

FIGURE 3-1:

Analog Section of TC7116/TC7116A and TC7117/TC7117A

3.1.3

REFERENCE INTEGRATE PHASE

The final phase is reference integrate, or de-integrate.

Input low is internally connected to analog common

and input high is connected across the previously

charged reference capacitor. Circuitry within the chip

ensures that the capacitor will be connected with the

correct polarity to cause the integrator output to return

to zero. The time required for the output to return to

zero is proportional to the input signal. The digital

reading displayed is:

EQUATION 3-1:

3.1.4

REFERENCE

The positive reference voltage (VREF+) is referred to

analog common.

TC7116

TC7116A

TC7117

TC7117A

CREF

CREF+

CREF-

RINT

V+

CAZ

Auto-Zero

VINT

μA

INT

AZ & DE (±)

INT

Integrator

V+ -3V

Comparator

Digital

Section

DE (+)

(–)

(+)

DE (–)

V+

Analog

Common

VIN+

VIN-

VBUFF

CINT

VREF+

Low

Temp.

Drift

Zener

VREF

V-

–

1000 =

VIN

VREF

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