UCC2751
UCC3751
PRELIMINARY
Single Line Ring Generator Controller
FEATURES
DESCRIPTION
• Novel Topology for Low-Cost, Efficient The UCC3751 controller is designed for driving a power stage that gener-
Generation of Ring Voltage
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.
• 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
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.
• Primary Current Limiting to turn Power
Stage off under Fault Conditions
• Operates from a Single 12V Supply
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.
The circuits described in this datasheet are covered under US Patent #5,663,878 and other patents pending.
TYPICAL APPLICATIONS CIRCUIT
D1
R
SENSE
L
IN
T1
DC SIGNAL
C
DC
V
IN
V
V
1
12V
AC SIGNAL
C
C
F
R2
L
L
R
R
SAMPLING
CIRCUIT
OUT
12V
C
BYP1
9
12
2
6
4
C
R1
N:1
C
BYP2
VS12
11 DRV1
DRVS
RINGEN
OHD
VDD
ENABLE 10
Q1
UCC3751
5
DCLIM
DELAY
1
Q2
13 DRV2
GND
XTAL2 15
PGND
14
FS0
7
FS1
8
XTAL1
16
3
UDG-98047
3.579545MHz
SLUS267A - JULY 1999