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

ENABLE

VDD

OFFHOOK

XTAL2

OHD

N/C

DRVS

VS12

DRV1

DCLIM

DRV2

XTAL1

FS1

FS0

PGND

GND

BYP2

SAMPLING

CIRCUIT

AC SIGNAL

OUT

12V

DC SIGNAL

12V

N:1

BYP1

SENSE

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.

UCC2752
UCC3752

(TOP VIEW) DIL-16, SOIC-16
N or D Packages

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2V
Analog Inputs (OHD, DCLIM, XTAL1, XTAL2)

Maximum Forced Voltage. . . . . . . . . . . . . . . . . . . . 0.3 to 5V

Logic Inputs

Maximum Forced Voltage . . . . . . . . . . . . . . . . . . 0.3 to 7.5V

Reference Output Current (V

DD)

. . . . . . . . . . . Internally Limited

Output Current (DRV1, DRV2, DRVS) Pulsed . . . . . . . . . . 1.5A
Operating Junction Temperature . . . . . . . . . . 40°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . 65°C to +150°C

Note: Unless otherwise indicated, voltages are referenced to
ground and currents are positive into, negative out of, the spe-
cific terminals. Pulsed is defined as a less than 10% duty cycle
with a maximum duration of 500 S.

PGND

XTAL2

XTAL1

DRV2

DRVS

ENABLE

DRV1

VS12

N/C

OFFHOOK

FS1

OHD

FS0

GND

VDD

DCLIM

CONNECTION DIAGRAMS

FS1

FS0

MODE

Sine Wave

Frequency (Hz)

Table I. Frequency selectability decoding.

FS1

FS0

DRVS

FDRV FDRVS

89.469kHz

20Hz

89.464kHz

25Hz

89.439kHz

50Hz

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications hold for T

= 0°C to 70°C for the

UCC3752 and 40°C to +85°C for the UCC2752, T

= T

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

V12 Supply Current Section

Supply Current

ENABLE = 0V

0.5

ENABLE = 5V

0.5

Internal Reference with External Bypass Section

Output Voltage (V

)

4.85

5.15

Load Regulation

0mA

2mA

Line Regulation

10V < V

12 < 13V, IV

= 1mA

Short Circuit Current

VDD = 0

Output Drivers Section (DRV1, DRV2)

Pull Up Resistance

LOAD

= 10mA to 20mA

Pull Down Resistance

LOAD

= 10mA to 20mA

Rise Time

LOAD

= 1nF

100

Fall Time

LOAD

= 1nF

100

Output Drivers Section (DRVS)

Pull Up Resistance

LOAD

= 10mA to 20mA

Pull Down Resistance

LOAD

= 10mA to 20mA

Sample Pulse-Width

Mode 1 (Table 1)

240

280

320

Rise Time

LOAD

= 1nF

100

Fall Time

LOAD

= 1nF

100

UCC2752
UCC3752

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications hold for T

= 0°C to 70°C for the

UCC3752 and 40°C to +85°C for the UCC2752, T

= T

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Current Limit Section

DCLIM Threshold

250

300

350

DCLIM Input Current

DCLIM

= 0V

900

100

OffHook Detect Section

OHD Threshold

250

300

350

OHD Input Current

OHD

= 0V

900

100

Offhook V

OFFHOOK

= 1mA

3.0

4.0

Offhook V

OFFHOOK

= 1mA

1.0

1.5

Offhook Pull-Up Impedance

LOAD

= 0mA to 1mA

100

400

900

Offhook Pull-Down Impedance

LOAD

= 0mA to 1mA

100

250

900

Frequency Section (Table 1)

Primary Switching Frequency

All cases 3.579545 MHz Crystal

89489

Sampling Switching Frequency

FS0 = 0, FS1 = 0, Mode 1, (Table 1)

89469

FS0 = 1, FS1 = 0, Mode 1

89464

FS0 = 0, FS1 = 1, Mode 1

89439

PIN DESCRIPTIONS

DCLIM: Primary current sense input. Signal proportional
to the primary switch current. All outputs are turned off
when a threshold of 300mV is exceeded on this pin. This
current-limit works on a cycle-by-cycle basis.

DRV1, DRV2: Low impedance driver outputs for the pri-
mary switches. DRV1 and DRV2 are complimentary and
have 50% duty cycle.

DRVS: Low impedance driver output for the sampling
switch(es). The pulse width of this output is 280ns.
Typically, a pulse transformer is used to couple the short
sampling pulses at DRVS to the floating sampling
switch(es).

ENABLE: Logic input which turns off the outputs when
low.

FS0, FS1: Frequency select pins for determining the dif-
ference frequency between primary and secondary
pulses under normal operation. These pins can be hard-
wired to GND or VDD to get one of the available output
frequencies (20,25 and 50 Hz). See Table 1 in the spec
table.

GND: Reference point for all the internal voltages and
common return for the device.

OFFHOOK: Output indicating the off-hook condition. This
signal can be used by an external circuit to switch to a
line from the ring generator output to the DC voltage.

OHD: Off-Hook Detect. Voltage proportional to output cur-
rent DC level is fed into this pin and compared to an inter-
nal threshold of 300mV. If the threshold is exceeded, the
OFFHOOK output goes high.

PGND: Return point for the output drivers. Connect to
GND at a single point in the circuit.

VDD: Internal regulated 5V supply. This voltage is used to
power all the internal precision circuits of the IC. This pin
needs to be bypassed to GND with ceramic capacitor.

VS12: External 12V power supply for the IC. Powers VDD
and provides voltage for the output drivers.

XTAL1, XTAL2: Pins for connecting precision Crystal to
attain the accurate output frequencies. An external
square-wave pulse can also be applied to XTAL2 if XTAL1
is tied to VDD/2.

UCC2752
UCC3752

Power Stage Operation

The power stage used for the UCC3752 application has
two distinct switching circuits which together produce the
required low frequency signal on the output. The primary
side switching circuit consists of a current fed push-pull
resonant circuit that generates the high frequency sinu-
soidal waveform across the transformer winding. The op-
eration of this type of circuit is extensively covered in
Unitrode Application notes U-141 and U-148. Resonant
components C

, C

, L

, N should be chosen so that

the

primary

and

secondary

resonances

are

well

matched. Also, for the UCC3752 operation, switching fre-
quency is fixed by crystal selection. So, the resonant
components must be selected to yield a resonant fre-
quency close enough to the switching frequency to get a
low distortion sine-wave. Practically, since it is impossi-
ble to get an exact match between the two frequencies,
the switching frequency should always be higher than
the resonant frequency to ensure low distortion and take
advantage of ZVT operation. Switches Q1 and Q2 are
pulsed at 50% duty cycle at the switching frequency
(89.489 kHz) determined by a crystal (3.579545 MHz)
connected to the UCC3752. The input voltage for the
resonant stage (typically 12V) determines the voltage

stress of Q1 and Q2. Transformer turns ratio is
determined by the output voltage requirements. On the
secondary side, the high frequency waveform is sampled
at a predetermined frequency (e.g. 89.469 kHz) which dif-
fers from the primary switching frequency by the desired
output frequency (e.g. 20 Hz). The sampling is accom-
plished using a bi-directional switching circuit as shown in
Figure 1 and Figure 2. Figure 1 shows the sampling
mechanism consisting of two back-to-back FET switches
allowing current flow in both directions. The sampling can
also be done with a single active switch and a full-bridge
rectifier as shown in Fig. 2. The DRVS pin of the
UCC3752 provides the drive signal for the sampling
switch(es) and this signal is coupled through a pulse
transformer. Typical pulsewidth of the sampling signal is
280nS. As a result of sampling, the resultant output sig-
nal matches the secondary voltage in amplitude and has
a low output frequency desired for ring generation.

The secondary winding of the power transformer also has
a tap (or a separate winding) to generate a loosely regu-
lated DC voltage. This DC voltage can be used to offset
the ring generator output. It an also be used as a power
supply for supplying talk battery voltage in some applica-
tions.

APPLICATION INFORMATION

OHD

DRV1

DCLIM

OFFHOOK

FS0

FS1

DRVS

VDD

GND

VS12

DRV2

PGND

5 VOLT

REFERENCE

ONE-SHOT

1/F

OSC

4.5V

MODULO

3,560

COUNTER

MODULO

1,800

COUNTER

MODULO

4,480

COUNTER

2/F

OSC

ONE-SHOT

300mV

XTAL2

MODULO

COUNTER

MODULO

COUNTER

XTAL1

ENABLE

N/C

300mV

MODULO

COUNTER

1-SHOT

BLOCK DIAGRAM

UDG-98023

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Mailing Address:

Texas Instruments
Post Office Box 655303
Dallas, Texas 75265

2001, Texas Instruments Incorporated

IMPORTANT NOTICE

Customers are responsible for their applications using TI components.

In order to minimize risks associated with the customer's applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.

Resale of TI's products or services with

statements different from or beyond the parameters stated by TI for

Also see: Standard Terms and Conditions of Sale for Semiconductor Products. www.ti.com/sc/docs/stdterms.htm

Mailing Address:

Texas Instruments
Post Office Box 655303
Dallas, Texas 75265

2001, Texas Instruments Incorporated

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