CD22859

Features:

• Mute Drivers On-Chip
• Device Power can Either be Regulated DC or Telephone Loop Current
• Use of an Inexpensive 3.579545MHz TV Crystal Provides High Accuracy and Stability for all Frequencies


Application

• For Use In Dual-tone Telephone Dialing Systems


Pinout




Specifications

Supply Voltage (V_DD - V_SS). . . . . . . . . . . . . . . . . . . . . . . -0.5 to 12V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . .. -0.5V to V_DD 0.5V
Power Dissipation, P_D
T_A = -40 to 60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500mW
T_A = 60 to 85 . . . . . . . Derate Linearly at 1.2mW/ to 200mW


Description

The CD22859 is a CMOS dual-tone multifrequency (DTMF) tone generator for use in dual-tone telephone dialing systems. The device can easily be interfaced to a standard push-button telephone keyboard to provide enabling operation directly with the telephone lines.
The CD22859 generates standard DTMF sinusoidal dialing tones from an on-chip reference crystal oscillator. The reference oscillator uses an inexpensive 3.579545MHz color TV crystal to create highly stable and accurate tones. The sinusoidal tones are digitally synthesized by a stair-step approximation.

One of four low-frequency band row tones and one of four high-frequency band column tones are selected by driving one of the four row inputs and one of the four column inputs low. Simultaneous selection of more than one row input and/or more than one column input will inhibit tone generation, or generate a single-tone sinusoid. These operating modes CD22859 are described in the functional truth table.

CD22859 Control logic is included to allow easy interface to standard K500-type telephones. Two CMOS outputs (T_X, R_X) capable of driving external pnp receiver and transmitter muting transistors are provided. A low input to the CD pin inhibits tone generation, turns off the reference oscillator and causes T_X and R_X outputs to go to logic '0'. During tone generation mode, CD = 1 and T_X, R_X = logic 1.

The row, column and CD inputs CD22859 are provided with pull-up resistors to allow the use of SPST switch matrixes.