June 1999 TOKO, Inc.

Page 9

TK15211

APPLICATION INFORMATION

KEY INPUT CIRCUIT

Figure 10 illustrates the KEY input equivalent circuit. When

the control pin is open, the input is pulled up to a high level

(approximately 1.4 V). This applies the channel A input

signal to the output. A low level changes the output to the

channel B input signal. When the control terminal is pulled

low, a current up to 30

µA may flow out of the terminal. For

this reason, an external resistor value must be selected

which results in a voltage of less than 0.8 V to maintain a low

condition.

SWITCHING TIME

This time is the signal change response time compared to

the control key input signal. Figure 11 illustrates the timing

chart. T = 2

µs typically.

APPLICATION

Figure 12 illustrates an example of a typical application.

The standard application of the TK15211M is to use direct

coupling at the inputs and capacitor coupling at the output.

For characteristics of distortion and dynamic range versus

R

refer to the graphs in the Typical Performance

Characteristics. The TK15211M can also be used with

capacitor coupling on the inputs, but an external bias

supply is required. If capacitor coupling is desired, it is

recommended to use the TK15210M with built-in bias. The

DC input bias of the TK15210M is V

CROSS TALK

Figure 13 is an example of a layout pattern. Because the

TK15211M is direct coupled, the influence of the

application is minimal. However, in the capacitor coupled

application of the TK15211M, the following must be

considered. Because of the high impedance at the inputs,

the capacitors can act as antennas to each other. If the

parts are bigger, and the space between the capacitors is

too narrow, then cross talk will increase. Therefore, when

designing the printed circuit pattern, separate the input

capacitors as far as possible and use as small a part as

possible (e.g., surface mount types, etc.).

Key in

to Logic

Figure 10

Key in

Bch (Ach)

SW out

50%

Ach (Bch)

t

Figure 11

VCC

+

33 µF

Key

+

inA

10 µF

out

RL

inB

Figure 12

Figure 13