UBA1702AT datasheet(6/24 Pages) PHILIPS

6 / 24 page

1997 Sep 29

Philips Semiconductors

Product speciﬁcation

Line interrupter driver and ringer

UBA1702; UBA1702A

FUNCTIONAL DESCRIPTION

The values given in this functional description are typical

values except when otherwise specified.

Speech part

The speech part consists of three blocks, the switch driver,

the line current management and the mute switch (DMO or

NSA) combined with an adjustable over-voltage (zener)

protection circuit. The reference block, which generates

reference voltages and currents, is also used in the speech

part (see Fig.1) by the mute switch block.

SWITCH DRIVER (PINS SDI, SDO, EHI AND DPI)

UBA1702

The UBA1702 switch driver block is intended to generate

the appropriate signal to drive an external PMOST

interrupter. The source and gate of this PMOST are

respectively connected to SDI and SDO. The electronic

hook switch input (EHI) and the dialling pulse input (DPI)

signals control the state of this PMOST.

The EHI pin is provided with high voltage capability. When

the voltage applied at pin EHI is HIGH, the switch driver

block will start and generate the proper signals to switch on

the external PMOST interrupter.

When the telephone set is equipped with a mechanical

hook switch, pin EHI can be connected directly to the

switch driver input (pin SDI). For electronic hook switch

applications, the EHI pin can be driven by the

microcontroller output.

In some special applications, the EHI pin can be current

driven. In such a case, the current available at SDO to turn

on the PMOST interrupter is approximately 10 times the

EHI input current (providing IEHI <2 µA).

The EHI pin presents an impedance of 250 k

Ω at low input

voltage. When the applied voltage at EHI goes above

approximately 30 V, the EHI input current remains

constant (see Fig.3) so that the EHI impedance increases.

The DPI is designed to switch on or off the external

PMOST interrupter (providing EHI is HIGH). When the

voltage applied at pin DPI is HIGH, the switch driver block

turns off the external PMOST interrupter. When the

voltage applied at pin DPI is LOW, the switch driver block

turns on the external PMOST interrupter.

The external PMOST interrupter is controlled by the

voltage between the switch driver input and output

(pins SDI and SDO).

When the voltage applied at pin EHI is HIGH and the

voltage applied at pin DPI is LOW, the voltage at SDO is

pulled down to a value less than 0.2 V in order to create a

high source-gate voltage (VSG) for the external PMOST.

However, in order to avoid break-down of the external

PMOST, the voltage difference between SDI and SDO is

internally limited to 14 V.

When the voltage applied at pin EHI and the one applied

at pin DPI are both HIGH, pin SDO can be considered as

being connected to pin SDI via a 1.1 M

Ω pull-up resistor

while the impedance between SDI and VEE becomes very

high (a few M

Ω).

When the voltage applied at pin EHI is LOW, whatever the

one applied at DPI is, pin SDO can be considered as being

connected to pin SDI via a 1.1 M

Ω pull-up resistor while

the impedance between SDI and VEE becomes almost

infinite.

Fig.3 EHI input characteristics.

handbook, halfpage

100

200

400

IEHI

(

µA)

MGD178

300

VEHI (V)

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