TC530 datasheet(13/22 Pages) MICROCHIP

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DS21433B-page 13

TC530/TC534

5.0

SELECTING COMPONENT

VALUES FOR THE

TC530/TC534

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 5-1:

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. Rec-

ommended capacitors for CREF and CAZ are

shown in Table 5-1. Larger values for CAZ and

CREF mayalsobeused tolimit rollover errors.

TABLE 5-1:

CREF AND CAZ SELECTION

5.1

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 the

following equation.

EQUATION 5-2:

It is critical that the integrating capacitor have a very

low dielectric absorption. PPS capacitors are an exam-

ple of one such dielectric. Table 5-2 summarizes

various capacitors suitable for CINT.

TABLE 5-2:

RECOMMENDED CAPACITOR

FOR CINT

5.2

Calculate VREF

The reference de-integration voltage is calculated

using the following equaton:

EQUATION 5-3:

5.3

Serial Port

Communication with the TC530/TC534 is accom-

plished 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.

5.4

Data Read Cycle

Data is shifted out of the serial port in the following

order: End of Conversion (EOC), Overrange (OVR),

Polarity (POL), conversion data (MSB first). When R/W

is high, the state of the EOC bit can be polled by simply

reading the state of DOUT. This allows the processor to

determine if new data is available without connecting

an additional wire to the EOC output pin (this is espe-

cially useful in a polled environment). See Figure 5-1.

FIGURE 5-1:

SERIAL PORT DATA

READ CYCLE

Conversion

Per Second

Typical Value of

CREF,CAZ (µF)

Suggested* Part

Number

0.1

SMR5 104K50J0IL

2 to 7

0.22

SMR5 224K50J2L

2 or less

0.47

SMR5 474K50J04L

Note:

*Manufactured by Evox-Rifa, Inc.

VINMAX

RINT =

Ω

where:

VIN(MAX) = Maximum Input Voltage (full count voltage)

RINT = Integrating Resistor (in mΩ)

For loop stability, RINT should be ≥ 50kΩ.

(TINT)(20 x10

-6)

(VS -0.9)

CINT =

µF

where: TINT = Integration Period

VS =IVDDI

CINT = Integrated Capacitor Value (µF).

Value (

µF)

Suggested Part Number*

0.1

SMR5 104K50J0IL

0.22

SMR5 224K50J2L

0.33

SMR5 334K50J03L4

0.47

SMR5 474K50J04L

Note:

*Manufactured by Evox-Rifa, Inc.

(VS –0.9) (CINT)(RINT)

VREF =

2(RINT)

EOC OVR POL MSB

LSB

R/W

DCLK

DOUT

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