FX105AP3 datasheet(9/16 Pages) CMLMICRO

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Tone Detector

FX105A

D/105A/5

1.6.2.7 Calculate RWC3A (C3A = C3B) Use nearest preferred values.

RWC3A » TWORD/ [-3In (1 - VTH/ VIN

MIN

) ]

where VTH is the word filter

sensitivity, see Section 1.7.1

A signal amplitude of 200mV and a resistor value RW of 465kΩ with a 220nF capacitor for C3A and

C3B will yield a TWORD time of 41msec. This in turn yields a response time of 9msec + 41msec =

50msec.

1.6.2.8 Calculate the Maximum De-response Time

TOFF » -3 RWC3A In (VTH/ VIN

MAX

)

where VTH is the word filter

sensitivity, see Section 1.7.1

For improved de-response time, a diode (1N914 or similar) can be placed between pins 5 and 6, as

shown in Figure 2. The formula and figure below show the approximate time the FX105A will take to

turn off after an in-band signal has been removed. The effect of this diode is to greatly reduce the

turn-off time with signal input amplitudes greater than 300mVrms. Figure 4 is for VDD = 5V; for lower

VDD then KDT increases.

TOFF » KDTRWC3A

So for a maximum signal amplitude of 400mV, a resistor value RW of 465kΩ with a 220nF capacitor

for C3A and C3B and a diode between pins 5 and 6, a de-response time of ≈ 363msec is obtained.

Figure 4 KDT Factor for TOFF vs. Signal Input Amplitude

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