BU8874

Communication ICs DTMF receiver for telephones BU8874 / BU8874F The BU8874 and BU8874F are DTMF receiver ICs developed for use in telephone answering machines, and convert 16 different types of DTMF signals into 4-bit binary serial data. In addition to a compact 8-pin DIP (BU8874) package, these receivers feature a wide dynamic range, eliminating the need for an external input amplifier. Expertise from a number of companies has been incorporated into these products to enable guard time control through a host microcontroller. FApplications Telephone answering machines FFeatures 1) Dynamic range of 45dB. (internal AGC) 2) Power down mode. 3) 4-bit binary serial data output. 4) Guard time can be controlled through host microcontroller. 5) Input pins equipped with hysteresis. (ACK pin) FBlock diagram 6) 4.19MHz crystal resonator can be used. 7) 8-pin DIP package. (BU8874) 202 Communication ICs FAbsolute maximum ratings (Ta=25_C) BU8874 / BU8874F FRecommended operating conditions (Ta=25_C) FPin descriptions 203 Communication ICs FInput / output circuits INPUT PWDN BU8874 / BU8874F OSC ACK SD ESt 204 Communication ICs FElectrical characteristics (unless otherwise noted, Ta=25_C, VDD=5.0V) BU8874 / BU8874F 205 Communication ICs FCircuit operation (1) An overview of operation A DTMF signal is supplied to the INPUT pin and applied to a pair of 6th-order bandpass filters, which separate the DTMF signal into its high (COL) and low (ROW) frequencies. The separated tones...