TC510 datasheet(12/34 Pages) MICROCHIP

12 / 34 page

TC500/A/510/514

DS21428D-page 12

7.0

TYPICAL APPLICATIONS

7.1

Component Value Selection

The procedure outlined below allows the user to arrive

at values for the following TC5XX design variables:

Integration Phase Timing.

Integrator Timing Components (RINT, CINT).

Auto-zero and Reference Capacitors.

Voltage Reference.

7.2

Select Integration Time

Integration time must be picked as a multiple of the

period of the line frequency. For example, TINT times of

33 msec, 66 msec and 132 msec maximize 60 Hz line

rejection.

7.3

DINT and IZ Phase Timing

The duration of the DINT phase is a function of the

amount of voltage stored on the integrator during TINT

and the value of VREF. The DINT phase must be initiated

immediately following INT and terminated when an inte-

grator output zero-crossing is detected. In general, the

maximum number of counts chosen for DINT is twice

that of INT (with VREF chosen at VIN(MAX) /2).

7.4

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 in the

following equation:

EQUATION 7-1:

7.5

Select Reference (CREF) and Auto-

zero (CAZ) Capacitors

CREF and CAZ must be low leakage capacitors (such as

polypropylene). The slower the conversion rate, the

larger the value CREF must be. Recommended

capacitors for CREF and CAZ are shown in Table 7-1.

Larger values for CAZ and CREF may also be used to

limit rollover errors.

TABLE 7-1:

CREF AND CAZ SELECTION

7.6

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 7-2:

It is critical that the integrating capacitor has a very low

dielectric absorption. Polypropylene capacitors are an

example of one such dialectic. Polyester and poly-

bicarbonate capacitors may also be used in less critical

applications. Table 7-2 summarizes recommended

capacitors for CINT.

TABLE 7-2:

RECOMMENDED CAPACITOR

FOR CINT

7.7

Calculate VREF

The reference de-integration voltage is calculated

using the following equation:

EQUATION 7-3:

Where:

VIN(MAX) = Maximum input voltage (full count voltage)

RINT = Integrating Resistor (in MΩ)

For loop stability, RINT should be ≥ 50 kΩ.

INT in MΩ

()

IN MAX

()

-----------------------

Conversions

Per Second

Typical Value of

CREF, CAZ (μF)

Suggested* Part

Number

0.1

SMR5 104K50J01L4

2 to 7

0.22

SMR5 224K50J02L4

2 or less

0.47

SMR5 474K50J04L4

* Manufactured by Evox Rifa, Inc.

Value

Suggested

Part Number*

0.1

SMR5 104K50J01L4

0.22

SMR5 224K50J02L4

0.33

SMR5 334K50J03L4

0.47

SMR5 474K50J04L4

* Manufactured by Evox Rifa, Inc.

Where:

TINT = Integration Period

VS = IVDDI or IVSSI, whichever is less (TC500/A)

VS = IVDDI (TC510, TC514)

IN T

() 20 10

–

()

0.9

–

()

---------------------------------------------

REF

0.9

–

() C

INT

() R

INT

()

INT

()

-----------------------------------------------------------V

TC510 数据表(PDF) 12 Page - Microchip Technology

TC510 数据表(HTML) 12 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

数据表下载