UBA1702AT View Datasheet(PDF) - Philips Electronics

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UBA1702AT

Line interrupter driver and ringer.

Philips Electronics 

Philips Semiconductors

Line interrupter driver and ringer

Product specification

UBA1702; UBA1702A

MUTE SWITCH AND ZENER PROTECTION

(PINS MSI, MSA AND ZPA)

The mute switch is, in fact, a switchable and electronic

zener diode connected between the speech part output

(pin SPO) and VEE.

When the voltage applied at the mute switch input

(pin MSI) is LOW, the switch is in over-voltage protection

mode and the maximum SPO voltage is limited to 12 V.

This level can be increased or decreased by connecting a

resistor between pins ZPA (zener protection adjustment)

and VEE or ZPA and SPO respectively.

When the voltage applied at pin MSI is HIGH, the switch is

in mute mode (DMO or NSA) resulting in a SPO voltage

below 3 V. This level can be decreased by connecting a

resistor between pins MSA (mute switch adjustment) and

SPO. It should be noted that the mute switch stage is

supplied from VDD thus a minimum voltage of

approximately 2.1 V is required on VDD.

REFERENCE

The bias currents and voltages for the various speech

blocks are generated by the reference block which is, in

most cases, supplied from pin SPO. This block guarantees

a high AC impedance at the SPO pin operating down to a

low SPO voltage. Therefore, most speech part blocks

operate independently from VDD.

Ringer part

The ringer part consists of five blocks, the ringer

protection, the ringer threshold, the ringer frequency

detection, the volume control and the piezo driver.

The reference block which generates reference voltages

and currents is also used in the ringer part (see Fig.1).

RINGER PROTECTION (PINS RPI AND VRR)

The ringer protection block converts the ringing current

into a limited voltage between the ringer part input

(pin RPI) and VEE. This voltage is used (via an internal

diode) to generate the ringer supply voltage VRR which is

mainly used for all ringer parts. The voltage at pin VRR

must be filtered with a 22 µF capacitor connected between

pins VRR and VSS.

In electronic hook switch applications and also in speech

mode (see Fig.8), pin RPI is always connected to the

telephone line (through a series RC network and a diode

bridge). In order not to disturb normal speech operation, a

high AC impedance is present at pin RPI (providing the

speech level is less than 1.5 V (RMS) i.e. 5.7 dBm).

In the DMO or NSA mode (i.e. MSI is HIGH), the voltage

across RPI and VEE is limited to 2.1 V. With this feature

and in electronic hook switch applications, several

additional ringers can be placed in parallel without tinkling

during pulse dialling phase.

RINGER THRESHOLD (PIN RTA)

The piezo driver is internally enabled when the voltage at

pin VRR exceeds a threshold level of 11 V. This threshold

level can be increased or decreased by connecting a

resistor between pins RTA (ringer threshold adjustment)

and VSS or RTA and VRR respectively.

Because of the built-in 6.5 V hysteresis, a voltage change

at pin VRR (coming from current consumption increase

when the piezo output is driven with a melody) will have no

influence on this internal enabling signal.

RINGER FREQUENCY DETECTION (PIN RFO)

The ringer frequency detection block generates a square

wave signal at the ringer frequency output (pin RFO) with

twice the ringer signal frequency. This RFO signal can be

used by the microcontroller for frequency discrimination.

When the voltage at pin RPI drops below the voltage at

pin VDD, RFO goes LOW. Pin RFO goes HIGH when the

voltage at pin RPI exceeds the voltage at pin VRR.

This VRR − VDD hysteresis allows the frequency detection

circuit to ignore parasitic signals superimposed on the

ringing signal.

The voltage at pin EHI must be LOW to get a square wave

at pin RFO. When the voltage at pin EHI is LOW, the

voltage at pin RFO is always HIGH whatever the one at pin

RPI is.

VOLUME CONTROL (PINS RV0, RV1 AND RV2)

The volume control input has three bits RV2, RV1 and RV0

to realize eight volume levels. The volume is controlled by

regulating the supply voltage of the piezo output stage.

The first six steps have a fixed value of 6 dB, the value of

the last step (maximum volume) is dependent on the

available voltage at pin VRR.

Default setting during start-up is (RV2 = 0, RV1 = 0,

RV0 = 0) which corresponds to minimum volume. In order

not to damage the piezo transducer, the differential output

ROA − ROB is internally limited to a value less than

32 V (p-p).

1997 Sep 29

8

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