TK14551V/14551 TOKO [TOKO, Inc], TK14551V/14551 Datasheet - Page 27

• Manufacturer Part Number: TK14551V/14551
• Description: FM IF DETECTOR/AMPLIFIER
• Manufacturer: TOKO [TOKO, Inc]

Battery Save Function:
Pin 21 is the control terminal for the battery save function. The ON/OFF operation of the whole IC can be switched by
controlling the DC voltage at this terminal. Figure 14 shows the internal equivalent circuit of Pin 21.
Because it switches the bias circuit of the whole IC using the transistor in standby mode, it reduces the supply current
to near zero. As the input terminal is connected with an electrostatic discharge protection diode at GND side only, it is
possible to control the voltage above the supply voltage. It is possible to go into standby mode by disconnecting Pin 21,
but it is not recommended because Pin 21 is a high impedance and may malfunction from an external disturbance.
When Pin 21 is disconnected, a suitable capacitor should be connected between Pin 21 and GND.
Application of ASK(Amplitude Shift Keying) Demodulation:
Figure 15 shows an example application of ASK demodulation.
If the application circuit is like Figure 15, the transient response time is long because of the time constant of the rectifier
(Pin 12) of the data comparator input.
On the other hand, if the circuit construction between the RSSI buffer amplifier output-2 (Pin 10) and the data comparator
input is Figure 16, the transient response time is shortened. Since the demodulation is a logarithmic detection using the
RSSI output, the demodulated wave of the RSSI buffer amplifier output-2 is distorted making the duty ratio of the data
comparator output worse. The output duty ratio may be improved by adding the offset DC voltage (Vs) to the DC voltage
of Pin 11 of the data comparator input. Vs is established at a few tens of mV. But, as the demodulation level of the RSSI
buffer amplifier output-2 is changed by the dispersion, it is best to control Vs by a variable resistor, etc. It is possible to
substitute the variable resistor for Vs.
CIRCUIT DESCRIPTION
January 2000 TOKO, Inc.
FIGURE 14 - BATTERY SAVE
Vs
21
50 K
BIAS
V CC
TK14551V
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