TC9400 Просмотр технического описания (PDF) - Microchip Technology

Номер в каталоге

Компоненты Описание

производитель

TC9400

Voltage-to-Frequency/Frequency-to-Voltage Converters

Microchip Technology 

TC9400/9401/9402

3.2 Voltage-to-Time Measurements

The TC9400 output can be measured in the time

domain as well as the frequency domain. Some micro-

computers, for example, have extensive timing capabil-

ity, but limited counter capability. Also, the response

time of a time domain measurement is only the period

between two output pulses, while the frequency mea-

surement must accumulate pulses during the entire

counter time-base period.

Time measurements can be made from either the

TC9400's PULSE FREQ OUT output, or from the

FREQ/2 OUT output. The FREQ/2 OUT output

changes state on the rising edge of PULSE FREQ

OUT, so FREQ/2 OUT is a symmetrical square wave at

one-half the pulse output frequency. Timing measure-

ments can, therefore, be made between successive

PULSE FREQ OUT pulses, or while FREQ/2 OUT is

high (or low).

4.0 PIN FUNCTIONS

4.1 Threshold Detector Input

In the V/F mode, this input is connected to the AMPLI-

FIER OUT output (Pin 12) and triggers a 3µsec pulse

when the input voltage passes through its threshold. In

the F/V mode, the input frequency is applied to this

input.

The nominal threshold of the detector is half way

between the power supplies, or (VDD + VSS)/2 ±400mV.

The TC9400's charge balancing V/F technique is not

dependent on a precision comparator threshold,

because the threshold only sets the lower limit of the

Op Amp output. The Op Amp's peak-to-peak output

swing, which determines the frequency, is only

influenced by external capacitors and by VREF.

4.2 Pulse Freq Out

This output is an open drain N-channel FET, which pro-

vides a pulse waveform whose frequency is propor-

tional to the input voltage. This output requires a pull-

up resistor and interfaces directly with MOS, CMOS,

and TTL logic (see Figure 4-1).

FIGURE 4-1:

FOUT

OUTPUT WAVEFORMS

3µsec

Typ.

FOUT/2

1/f

Amp Out

VREF

0V

CREF

CINT

Notes:

1. To adjust FMIN, set VIN = 10mV and adjust the 50kΩ offset for 10Hz output.

2. To adjust FMAX, set VIN = 10V and adjust RIN or VREF for 10kHz output.

3. To increase FOUTMAX to 100kHz, change CREF to 2pF and CINT to 75pF.

4. For high performance applications, use high stability components for RIN, CREF, VREF (metal film

resistors and glass capacitors). Also, separate output ground (Pin 9) from input ground (Pin 6).

DS21483B-page 8

© 2002 Microchip Technology Inc.

Share Link: