UBA1702A datasheet(7/24 Pages) PHILIPS

7 / 24 page

1997 Sep 29

Philips Semiconductors

Product speciﬁcation

Line interrupter driver and ringer

UBA1702; UBA1702A

UBA1702A

The UBA1702A switch driver block is intended to generate

the appropriate signal to drive an external PNP interrupter.

The emitter and base of this PNP are respectively

connected to SDI and SDO. The EHI and DPI signals

control the state of this PNP.

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 appropriate signals to

switch on the external PNP interrupter.

When the telephone set is equipped with a mechanical

hook switch, pin EHI can be connected directly to pin SDI.

For electronic hook switch applications, the EHI pin can be

driven by the microcontroller output.

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 PNP

interrupter (providing EHI is HIGH). When the voltage

applied at pin DPI is HIGH, the switch driver block turns off

the external PNP interrupter. When the voltage applied at

pin DPI is LOW, the switch driver block turns on the

external PNP interrupter.

The external PNP interrupter is controlled by the current

flowing into pin SDO.

When the voltage applied at pin EHI is HIGH and the

voltage applied at pin DPI is LOW, pin SDO can be

considered as being connected to pin VEE via a 2.2 kΩ

resistor in order to create a base current for the external

PNP.

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.

LINE CURRENT MANAGEMENT

(PINS SPI, SPO, CDA, CLA AND CDO)

The line current is measured by an internal 2

Ω resistor

and a sense circuit connected between the speech part

input and output (pins SPI and SPO). The circuit delivers

information about the hook switch status at the current

detection output (pin CDO) and controls the line current

limitation.

When the SPI current exceeds a certain level (3 mA), the

sense circuit injects some image of the SPI current into an

internal resistor (see Fig.1). The created voltage becomes

higher than an internal reference (approximately 0.3 V)

and CDO goes HIGH. This current detection level can be

increased by connecting a resistor between pins CDA

(current detection adjustment) and VEE. It is also possible

to connect a capacitor between pins CDA and VEE to filter

unwanted AC components of the line current signal. Line

current interruption during pulse dialling influences the

CDO output.

When the SPI current exceeds another current level

(45 mA), the sense circuit injects some image of the SPI

current into an internal resistor (see Fig.1). The created

voltage becomes higher than an internal reference

(approximately 0.4 V) and an internal signal is generated

in order to limit the current in the external interrupter thus

resulting in a line current limitation. This line current

limitation level can be increased up to a maximum value of

120 mA by connecting a resistor between pins CLA

(current limitation adjustment) and VEE.

When a PMOST (UBA1702) is used as an interrupter, the

SPI current equals the drain or source current of the

PMOST and thus also equals the line current.

When a PNP (UBA1702A) is used as an interrupter, the

SPI current equals the collector current of the PNP and

thus differs from the line current (the PNP base current

does not flow into the SPI pin).

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