UBA1702AT datasheet(9/24 Pages) PHILIPS

9 / 24 page

1997 Sep 29

Philips Semiconductors

Product speciﬁcation

Line interrupter driver and ringer

UBA1702; UBA1702A

RINGER MELODY INPUT AND PIEZO DRIVER

(PINS RMI, ROA AND ROB)

The input signal at the ringer melody input (pin RMI) may

be a square wave or a sine wave which is generated by the

microcontroller. The input stage incorporates a small

hysteresis (between 0.48VDD and 0.52VDD) and is

referenced to 1

⁄

2VDD which is also the DC level of the signal

coming from the microcontroller. Nevertheless, when a

sine wave is used, a coupling capacitor of 10 nF

(connected between pin RMI and the output of the

microcontroller) is required. This 10 nF capacitor value is

enough since the RMI input impedance is approximately

250 k

Ω.

The piezo driver is an output stage for a piezo transducer

which has to be connected between ringer output A and

ringer output B (pins ROA and ROB) as a Bridged Tied

Load (BTL) or between ROA and VSS as a Single-Ended

Load (SEL). The ROA and ROB output signals are square

wave and in opposite phase driven by the ringer melody

input stage. The minimum output current capability of the

ROA and ROB outputs is greater than 80 mA at maximum

volume setting (RV2 = 1, RV1 = 1, RV0 = 1) and becomes

even greater during output switching. This gives fast rise

and fall times resulting in a lot of harmonics.

To obtain maximum efficiency, the piezo driver stage is

supplied in series with the VDD supply.

REFERENCE

The bias current for the various ringer blocks is generated

by the reference block while this block is supplied from pin

VRR or VDD.

Supply part (pins VBB and VDD)

The supply block regulates the voltage at pin VDD,

referenced to VSS, to a typical value of 3.3 V and can

deliver a minimum of 2 mA. This is sufficient to supply

most normal microcontrollers. The voltage at pin VDD must

be filtered with a 22

µF capacitor connected between

pins VDD and VSS.

In speech mode, this block is supplied from the

transmission circuit using pin VBB. The voltage drop

between VBB and VDD has been minimized (100 mV at

1 mA, providing 2.5 V < VBB < 3.0 V) in order to allow low

voltage operation of the transmission circuit.

In ringer mode, this block is supplied from the ringer part

using pin VRR and pin VBB which are tied together through

an internal diode (see Fig.1).

When an external (mains or battery) supply is connected

to VBB and no speech or ringer signal is applied, VDD

(3.3 V) is still present.

During on-hook phase, and when a small current is derived

from the line to the microcontroller supply, the circuit stays

in a kind of stand-by mode to provide sufficient voltage at

pin VDD. This is done to ensure memory retention in the

microcontroller.

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