TC9401 datasheet(11/24 Pages) MICROCHIP

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DS21483C-page 11

TC9400/9401/9402

5.2.3

CREF

The exact value is not critical and may be used to trim

the full scale frequency (see Section 7.1 “Input/Out-

put

Relationships”,

Input/Output

Relationships).

Glass film or air trimmer capacitors are recommended

because of their stability and low leakage. Locate as

close as possible to Pins 5 and 3 (see Figure ).

FIGURE 5-1:

Recommended C

REF vs.

REF

5.2.4

VDD, VSS

Power supplies of ±5V are recommended. For high

accuracy requirements, 0.05% line and load regulation

and 0.1

μF disc decoupling capacitors, located near the

pins, are recommended.

5.3

Adjustment Procedure

Figure 3-1 shows a circuit for trimming the zero loca-

tion. Full scale may be trimmed by adjusting RIN, VREF,

or CREF. Recommended procedure for a 10 kHz full

scale frequency is as follows:

Set VIN to 10 mV and trim the zero adjust circuit

to obtain a 10 Hz output frequency.

Set VIN to 10V and trim either RIN, VREF, or CREF

to obtain a 10 kHz output frequency.

If adjustments are performed in this order, there should

be no interaction and they should not have to be

repeated.

5.4

Improved Single Supply V/F

Converter Operation

A TC9400, which operates from a single 12 to 15V vari-

able power source, is shown in Figure 5-2. This circuit

uses two Zener diodes to set stable biasing levels for

the TC9400. The Zener diodes also provide the refer-

ence voltage, so the output impedance and tempera-

ture coefficient of the Zeners will directly affect power

supply rejection and temperature performance. Full

scale adjustment is accomplished by trimming the input

current.

Trimming the reference voltage is not recommended

for high accuracy applications unless an op amp is

used as a buffer, because the TC9400 requires a low-

impedance reference (see Section 4.9 “VREF”, VREF

pin description, for more information).

The circuit of Figure 5-2 will directly interface with

CMOS logic operating at 12V to 15V. TTL or 5V CMOS

logic can be accommodated by connecting the output

pull-up resistors to the +5V supply. An optoisolator can

also be used if an isolated output is required; also, see

Figure 5-3.

500

400

300

200

100

-1

-2

-3

-4

-5

-6

-7

VREF (V)

10 kHz

100 kHz

VDD = +5V

VSS = -5V

RIN = 1MW

VIN = +10V

TA = +25°C

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