TC534COI データシートの表示（PDF） - TelCom Semiconductor, Inc

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TC534COI

5V PRECISION DATA ACQUISITION SUBSYSTEMS

TelCom Semiconductor, Inc 

5V PRECISION DATA ACQUISITION

SUBSYSTEMS

1

TC530

TC534

Auto Zero Phase (AZ)

This phase compensates for errors due to buffer, inte-

grator and comparator offset voltages. During this phase, an

internal feedback loop forces a compensating error voltage

on auto zero capacitor (CAZ). The duration of the AZ phase

is programmable via the serial port (see also Programming

AZ and INT Phase Duration paragraph of this document).

Input Integrate Phase (INT)

In this phase, a current directly proportional to differen-

tial input voltage is sourced into integrating capacitor CINT.

The amount of voltage stored on CINT at the end of the INT

phase is directly proportional to the applied differential input

voltage. Input signal polarity (sign bit) is determined at the

end of this phase. Converter resolution and conversion

speed is a function of the duration of the INT phase, which

is programmable by the user via the serial port (see also

Programming AZ and INT Phase Duration paragraph of this

document). The shorter the integration time, the faster the

speed of conversion, but the lower the resolution. Con-

versely, the longer the integration time, the greater the

resolution, but at slower the speed of conversion.

Reference Deintegrate Phase (DINT)

This phase consists of measuring the time for the

integrator output to return (at a rate determined by the

external reference voltage) from its initial voltage to 0V. The

resulting timer data is stored in the output shift register as

converted analog data.

Integrator Output Zero Phase (IZ)

This phase guarantees the integrator output is at zero

volts when the AZ phase is entered so that only true system

offset voltages will be compensated for.

All internal converter timing is derived from the fre-

quency source at OSCIN and OSCOUT. This frequency

source must be either an externally provided clock signal, or

an external crystal. If an external clock is used, it must be

connected to the OSCIN pin and the OSCOUT pin must

remain floating. If a crystal is used, it must be connected

between OSCIN and OSCOUT and physically located as

close to the OSCIN and OSCOUT pins as possible. In either

case, the incoming clock frequency is divided by four and the

resulting clock serves as the internal TC530/534 timebase.

APPLICATIONS

Programming the TC530/534

AZ and INT Phase Duration:

These two phases have equal duration determined by

the crystal (or external) frequency and the timer initialization

byte (LOAD VALUE). Timing is selected as follows:

(1) Select Integration Time

2 Integration time must be picked as a multiple of the

period of the line frequency. For example, tINT times

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

line rejection.

(2) Estimate Crystal Frequency

Crystal frequencies as high as 2MHz are allowed.

Crystal frequency is estimated using:

2(R)

FIN = tINT

3

where: R = Desired Converter Resolution

(in counts)

FIN = Input Frequency (in MHz)

INT = Integration Time (in seconds)

(3) Calculate LOAD VALUE

[LOAD VALUE]10 = 256 –

(tINT)(FIN)

1024

4

FIN can be adjusted to a standard value during this step.

The resulting base -10 LOAD VALUE must be converted to

a hexadecimal number, then loaded into the serial port prior

to initiating A/D conversion.

DINT and IZ Phase Timing

5

The duration of the DINT phase is a function of the

amount of voltage stored on the integrator capacitor during

INT, and the value of VREF. The DINT phase is initiated

immediately following INT and terminated when an integra-

tor output zero-crossing is detected. In general, the maxi-

mum number of counts chosen for DINT is twice that of INT

(with VREF chosen at VIN(max)/2).

6

System RESET

The TC530/534 must be forced into the AZ state when

power is first applied. A .01µF capacitor connected from

RESET to VCC (or external system reset logic signal) can be

used to momentarily drive RESET high for a minimum of

100msec.

7 Selecting Component Values for the TC530/534

(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 20µA.

8 The value of RINT is therefore directly calculated as

follows:

TELCOM SEMICONDUCTOR, INC.

3-55

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