UCC2751

UCC3751

PRELIMINARY

DESCRIPTION

The UCC3751 controller is designed for driving a power stage that gener-

ates low frequency, high voltage sinusoidal signals for telephone ringing

applications. The controller and the power stage are most suitable for sin-

gle line applications where low cost, high efficiency and minimum parts

count are critical. In addition to providing the sinusoidal ringing signal, the

controller and the power stage are designed to provide the required DC

voltage across the output when the phone goes off-hook. The DC voltage

is also added as the offset to the ringing signal. This feature eliminates the

need to have a separate talk battery voltage power supply as well as relays

and drivers to switch between the ringing voltage and the talk battery.

The UCC3751 directly drives primary side switches used to implement a

push-pull resonant converter topology and transformer coupled sampling

switches located on the secondary of the converter. For normal ring signal

generation, the primary switching frequency and secondary sampling fre-

quency are precisely offset from each other by the ringing frequency to pro-

duce a high voltage low frequency alias signal at the output. The off-hook

condition is detected by sensing the AC current and when AC limit is ex-

ceeded, the sampling frequency is set to be equal to the primary switching

frequency to produce a DC output.

The drive signal frequencies are derived from a high frequency (3579545

Hz) crystal. The primary switching frequency is 89.488 kHz and the sam-

pling frequency is 20, 25 or 50 Hz less depending on the status of fre-

quency select pins FS0 and FS1.

Single Line Ring Generator Controller

FEATURES

• Novel Topology for Low-Cost, Efficient

Generation of Ring Voltage

• Provides DC Offset and “Talk Battery”

Voltage for Off-Hook Conditions

• Selectable 20, 25 and 50 Hz Ring

Frequency

• Secondary (AC) Current Limiting

Allows Removal of AC Voltage under

Off-Hook Conditions

• Primary Current Limiting to turn Power

Stage off under Fault Conditions

• Operates from a Single 12V Supply

SLUS267A - JULY 1999

1

10

15

4

ENABLE

VDD

DELAY

XTAL2

6

OHD

2

RINGEN

12

DRVS

9

VS12

5

11

13

DRV1

DCLIM

DRV2

16

XTAL1

8

FS1

7

FS0

14

PGND

3

GND

C

BYP2

SAMPLING

CIRCUIT

C

F

AC SIGNAL

V

OUT

V

1

C

R2

12V

C

DC

D1

DC SIGNAL

Q1

L

IN

V

IN

12V

T1

L

R

L

R

N:1

Q2

R

SENSE

UCC3751

3.579545MHz

C

R1

C

BYP1

TYPICAL APPLICATIONS CIRCUIT

UDG-98047

The circuits described in this datasheet are covered under US Patent #5,663,878 and other patents pending.