TC530 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TC530

5V Precision Data Acquisition Subsystems

Microchip Technology 

6.0 SELECTING COMPONENT

VALUES FOR THE

TC530/TC534

1. Calculate Integrating Resistor (RINT)

The desired full scale input voltage and amplifier

output current capability determine the value of

RINT. The buffer and integrator amplifiers each

have a full scale current of 20 µA. The value of

RINT is therefore directly calculated as follows:

EQUATION 6-1:

RINT(MΩ)

=

V----I--N----M----A---X--

20

Where:

VIN(MAX) = Maximum Input Voltage (full

count voltage)

RINT = Integrating Resistor (in MΩ)

For loop stability, RINT should be ≥ 50 kΩ.

2. Select Reference (CREF) and Auto Zero (CAZ)

Capacitors.

CREF and CAZ must be low leakage capacitors

(such as polypropylene). The slower the conver-

sion rate, the larger the value CREF must be.

Recommended capacitors for CREF and CAZ are

shown in Table 6-1. Larger values for CAZ and

CREF may also be used to limit rollover errors.

TABLE 6-1: CREF AND CAZ SELECTION

Conversion

Per Second

Typical Value

of CREF, CAZ

(µF)

Suggested (1) Part

Number

>7

0.1

SMR5 104K50J0IL

2 to 7

0.22

SMR5 224K50J2L

2 or less

0.47

SMR5 474K50J04L

Note 1: Manufactured by Evox-Rifa, Inc.

TC530/TC534

6.1 Calculate Integrating Capacitor

(CINT)

The integrating capacitor must be selected to maximize

integrator output voltage swing. The integrator output

voltage swing is defined as the absolute value of VDD

(or VSS) less 0.9V (i.e.,IVDD – 0.9VI or IVSS +0.9VI).

Using the 20 µA buffer maximum output current, the

value of the integrating capacitor is calculated using

Equation 6-2.

EQUATION 6-2:

Where:

CINT(μF)

=

(---T---I--N----T---)--(---2---0----×-----1---0---–---6---)

(VS – 0.9)

TINT = Integration Period

VS = IVDDI

CINT = Integrated Capacitor Value (µF)

It is critical that the integrating capacitor have a very

low dielectric absorption. PPS capacitors are an exam-

ple of one such dielectric. Table 6-2 summarizes

various capacitors suitable for CINT.

TABLE 6-2: RECOMMENDED CAPACITOR

FOR CINT

Value (µF)

Suggested Part Number(1)

Note 1:

0.1

SMR5 104K50J0IL

0.22

SMR5 224K50J2L

0.33

SMR5 334K50J03L4

0.47

SMR5 474K50J04L

Manufactured by Evox-Rifa, Inc.

6.2 Calculate VREF

The reference de-integration voltage is calculated

using the following equaton:

EQUATION 6-3:

VREF

=

-(--V----S----–----0---.--9---)--(---C----I--N----T---)--(--R----I--N----T---)

2(RINT)

V

6.3 Serial Port

Communication with the TC530/TC534 is

accomplished over a 3-wire serial port. Data is clocked

into DIN on the rising edge of DCLK and clocked out of

DOUT on the falling edge of DCLK. R/W must be HIGH

to read converted data from the serial port and LOW to

write the LOAD VALUE to the TC530/TC534.

© 2007 Microchip Technology Inc.

DS21433C-page 15

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