UCC2752

UCC3752

DESCRIPTION

The UCC3752 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 up to

5 line applications where low cost, high efficiency and minimum parts count

are critical. A semi-regulated DC voltage is added as an offset to the ring-

ing signal. The ring generator operation is non-isolated and open loop.

The UCC3752 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, a flag is generated on the OFFHOOK pin.

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

Hz) crystal. The primary switching frequency is 89.489 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.

Resonant Ring Generator Controller

FEATURES

• Novel Topology for Low-Cost, Efficient

Generation of Ring Voltage

• Suitable for Multi-Line Operation

• Selectable 20, 25 and 50 Hz Ring

Frequency

• Secondary (AC) Current Limiting

Generates an Off-Hook Detect Signal

• Primary Current Limiting to Turn

Power Stage Off Under Fault

Conditions

• Operates from a Single 12V Supply

JULY 1999 - REVISED AUGUST 2000 - SLUS269A

1

10

15

4

ENABLE

VDD

OFFHOOK

XTAL2

6

OHD

2

N/C

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

DC SIGNAL

Q1

L

IN

V

IN

12V

T1

L

R

L

R

N:1

Q2

D1

C

BYP1

R

SENSE

C

R1

3.579545MHz

UCC3752

TYPICAL APPLICATION

UDG-98058

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