TK14588 TOKO, TK14588 Datasheet - Page 18

• Manufacturer Part Number: TK14588
• Description: FM IF IC
• Manufacturer: TOKO

TK14588
CIRCUIT DESCRIPTION (CONT.)
Comparator (cont.):
Figure 11 shows the internal equivalent circuit of the comparator output stage. Because the comparator output is an open
collector, it is suitable for many interface levels. This open collector output is connected with an electrostatic discharge
protection diode at the GND side only; it is not connected with it at the power supply side in consideration of operating the
voltage over the supply voltage of this IC.
When the collector pull-up resistor value is low, high operating currents result. To prevent interference to the other circuitry,
the emitter of the output transistor is brought out independently at Pin 8.
Pin 8 is not connected with the substrate and other GND internal to the IC. Therefore, when operating this comparator,
this terminal must be connected to GND.
When the comparator is operating at high speed, the etch pattern of Pins 7 and 8 (comparator output stage) should not
be run close to the etch pattern of Pin 1 (IF input). The switching waveform of the comparator output may have an effect
on the IF input and may add noise to the zero crossing of the demodulated waveform, resulting in cross over distortion.
V CC
V CC
COMPARATOR
OUTPUT STAGE
FIGURE 11 - COMPARATOR OUTPUT STAGE
Power Save Function:
Pin 5 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 12 shows the internal equivalent circuit of Pin 5.
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 5, but it is not
recommended because Pin 5 is a high impedance and may malfunction by an external disturbance.
When Pin 5 is disconnected, a suitable capacitor should be connected between Pin 5 and GND.
V CC
BIAS
50 K
Vs
FIGURE 12
Page 18
January 2000 TOKO, Inc.