Typical Performance Characteristics

Diagram)

GENERAL

The LMC567 low power tone decoder can be operated at

supply voltages of 2V to 9V and at input frequencies ranging

from 1 Hz up to 500 kHz.

The LMC567 can be directly substituted in most LM567 ap-

plications with the following provisions:

1.

Oscillator timing capacitor Ct must be halved to double

the oscillator frequency relative to the input frequency

(See OSCILLATOR TIMING COMPONENTS).

2.

Filter capacitors C1 and C2 must be reduced by a factor

of 8 to maintain the same filter time constants.

3.

The output current demanded of pin 8 must be limited to

the specified capability of the LMC567.

OSCILLATOR TIMING COMPONENTS

The voltage-controlled oscillator (VCO) on the LMC567 must

be set up to run at twice the frequency of the input signal

tone to be decoded. The center frequency of the VCO is set

by timing resistor Rt and timing capacitor Ct connected to

pins 5 and 6 of the IC. The center frequency as a function of

Rt and Ct is given by:

Since this will cause an input tone of half F

This equation is accurate at low frequencies; however,

above 50 kHz (F

actual frequency to be lower than predicted.

The choice of Rt and Ct will be a tradeoff between supply

current and practical capacitor values. An additional supply

current component is introduced due to Rt being switched to

V

I

Thus the supply current can be minimized by keeping Rt as

large as possible (see supply current vs. operating fre-

quency curves). However, the desired frequency will dictate

an RtCt product such that increasing Rt will require a smaller

Ct. Below Ct = 100 pF, circuit board stray capacitances be-

gin to play a role in determining the oscillation frequency

which ultimately limits the minimum Ct.

To allow for I.C. and component value tolerances, the oscil-

lator timing components will require a trim. This is generally

accomplished by using a variable resistor as part of Rt, al-

though Ct could also be padded. The amount of initial fre-

quency variation due to the LMC567 itself is given in the

electrical specifications; the total trim range must also ac-

commodate the tolerances of Rt and Ct.

Supply Current vs.

Operating Frequency

DS008670-3

Bandwidth vs.

Input Signal Level

DS008670-7

Largest Detection

Bandwidth vs. Temp.

DS008670-8

Bandwidth as

a Function of C2

DS008670-9

Frequency Drift

with Temperature

DS008670-10

Frequency Drift

with Temperature

DS008670-11

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