ETC UCC2751N

UCC2751
UCC3751
Single Line Ring Generator Controller
FEATURES
DESCRIPTION
• Novel Topology for Low-Cost, Efficient The UCC3751 controller is designed for driving a power stage that generGeneration 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• Provides DC Offset and “Talk Battery”
gle line applications where low cost, high efficiency and minimum parts
Voltage for Off-Hook Conditions
count are critical. In addition to providing the sinusoidal ringing signal, the
• Selectable 20, 25 and 50 Hz Ring
controller and the power stage are designed to provide the required DC
Frequency
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
• Secondary (AC) Current Limiting
need to have a separate talk battery voltage power supply as well as relays
Allows Removal of AC Voltage under
and drivers to switch between the ringing voltage and the talk battery.
Off-Hook Conditions
• Primary Current Limiting to turn Power The UCC3751 directly drives primary side switches used to implement a
push-pull resonant converter topology and transformer coupled sampling
Stage off under Fault Conditions
switches located on the secondary of the converter. For normal ring signal
• Operates from a Single 12V Supply
generation, the primary switching frequency and secondary sampling frequency are precisely offset from each other by the ringing frequency to produce 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 exceeded, 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 sampling frequency is 20, 25 or 50 Hz less depending on the status of frequency 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
RSENSE
LIN
T1
DC SIGNAL
CDC
VIN
V1
12V
AC SIGNAL
CR2
LR
CF
SAMPLING
CIRCUIT
LR
N:1
Q1
Q2
12V
CBYP1
CR1
VOUT
9
12
2
6
4
VS12
DRVS
RINGEN
OHD
VDD
11
DRV1
5
DCLIM
13
DRV2
UCC3751
CBYP2
ENABLE
10
DELAY
1
XTAL2
GND
PGND
FS0
FS1
XTAL1
3
14
7
8
16
15
3.579545MHz
APRIL 1999 - REVISED AUGUST 2000 - SLUS267B
UDG-98047
UCC2751
UCC3751
CONNECTION DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14V
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 (VDD) . . . . . . . . . . . Internally Limited
Output Current (DRV1, DRV2, DRVS) Pulsed . . . . . . . . . . 1.5A
Operating Junction Temperature . . . . . . . . . . –55°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C
DIL-16, SOIC-16 (TOP VIEW)
N or D Packages
DELAY
1
16
XTAL1
RINGEN
2
15
XTAL2
GND
3
14
PGND
VDD
4
13
DRV2
DCLIM
5
12
DRVS
OHD
6
11
DRV1
FS0
7
10
ENABLE
FS1
8
9
VS12
Note: Unless otherwise indicated, voltages are referenced to
ground and currents are positive into, negative out of, the specific terminals. Pulsed is defined as a less than 10% duty cycle
with a maximum duration of 500 S.
BLOCK DIAGRAM
ENABLE
10
XTAL2
15
XTAL1
16
MODULO
20
COUNTER
MODULO
2
COUNTER
11
DRV1
13
DRV2
12
DRVS
14
PGND
3
GND
9
VS12
4
VDD
ONE-SHOT
DCLIM
5
PROGRAMMABLE
COUNTER
CLR
300mV
CLK
DELAY
1
OHD
6
2 BIT
A/D
ONE-SHOT
300mV
1/FOSC
RINGEN
2
FS1
8
MODULO
1,800
COUNTER
MODULO
3,560
COUNTER
FS0
2/FOSC
MODULO
40
COUNTER
ONE-SHOT
5 VOLT
REFERENCE
7
MODULO
4,480
COUNTER
4.5V
UDG-98020
2
UCC2751
UCC3751
Table I. Frequency selectability decoding.
FS1
FS0
MODE
0
0
1
1
OHD = 0.5
0
1
0
1
1
1
1
3
2
Sine Wave
Frequency (Hz)
20
25
50
0
0
RINGEN
OHD
FS1
FS0
FDRVS
1
1
1
0
X
0
0
0
X
1
0
0
1
X
X
0
1
0
X
X
89.469kHz
89.464kHz
89.439kHz
89.489kHz
89.489kHz
FDRV–
FDRVS
20Hz
25Hz
50Hz
0.0Hz
0.0Hz
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications hold for TA = 0°C to 70°C for the
UCC3751 and –40°C to +85°C for the UCC2751, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
V12 Supply Current Section
Supply Current
ENABLE = 0V
1.0
3.0
mA
ENABLE = 5V
1.0
3.0
mA
Internal Reference with External Bypass Section
Output Voltage (VDD)
4.85
Load Regulation
0mA ≤ IVDD ≤ 2mA
Line Regulation
10V < VS12 < 13V, IVDD = 1mA
Short Circuit Current
VDD = 0
5
5
5.15
V
5
20
mV
3
20
mV
10
mA
Output Drivers Section (DRV1, DRV2)
Pull Up Resistance
ILOAD = 10mA to 20mA
6
15
Pull Down Resistance
ILOAD = 10mA to 20mA
6
15
Rise Time
CLOAD = 1nF
50
100
nS
Fall Time
CLOAD = 1nF
50
100
nS
Pull Up Resistance
ILOAD = 10mA to 20mA
4
10
Pull Down Resistance
ILOAD = 10mA to 20mA
4
10
Output Drivers Section (DRVS)
Sample Pulse-Width
Mode 1 and 2, (Note 1)
280
320
nS
Rise Time
CLOAD = 1nF
240
50
100
nS
Fall Time
CLOAD = 1nF
50
100
nS
250
300
350
mV
–900
–100
250
300
350
mV
–900
–100
nA
Current Limit Section
OHD Threshold
OHD Input Current
VOHD = 0V
DCLIM Threshold
DCLIM Input Current
VDCLIM = 0V
nA
Frequency Section (Note 1)
Primary Switching Frequency
All cases 3.579545 MHz Crystal
89489
Hz
Sampling Switching Frequency
FS0 = 0, FS1 = 0, Mode 1, (Note 1)
89469
Hz
FS0 = 1, FS1 = 0, Mode 1
89464
Hz
FS0 = 0, FS1 = 1, Mode 1
89439
Hz
3
UCC2751
UCC3751
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications hold for TA = 0°C to 70°C for the
UCC3751 and –40°C to +85°C for the UCC2751, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
Off-Hook Sampling Delay (Note 2)
td0
VDELAY < 0.9V
td1
1.1V < VDELAY < 1.9V
td2
2.1V < VDELAY < 2.9V
td3
3.1V < VDELAY < 3.9V
756
td4
4.1V < VDELAY
1008
0
20
nS
252
280
308
nS
504
560
616
nS
840
924
nS
1120
1232
nS
Note 1. Frequency setting is as shown in the Frequency Selectability Decoding Table. Sine Wave Frequency = Primary – Sampling
Frequency.
Note 2. The delay function will delay the sample pulse from the rising edge of DRV2 to allow adjustment of the DC level provided
during Mode 2.
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.
frequencies (20,25 and 50 Hz). See Note 1 in the spec
table.
DELAY: A resistive divider from VDD to GND is programmed and fed into DELAY pin. The voltage at this pin
sets the phase difference between the sampling pulses
and primary pulses under off-hook condition. By programming the delay, desired level of DC voltage can be
attained at the ringer output when the OHD threshold is
exceeded.
OHD: Secondary current sense input. Voltage proportional to output current DC level is fed into this pin and
compared to an internal threshold of 300mV. If the threshold is exceeded, the sampling scheme is changed to
eliminate the AC component in the output voltage as required by the off-hook condition.
GND: Reference point for all the internal voltages and
common return for the device.
PGND: Return point for the output drivers. Connect to
GND at a single point in the circuit.
DRV1, DRV2: Low impedance driver outputs for the primary switches.
RINGEN: Logic input used to determine when the ring
signal is needed. When this signal is high and OHD low,
normal ring signal is available at the output of the ring
generator.
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).
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.
ENABLE: Logic input which turns off the outputs when
low.
VS12: External 12V power supply for the IC. Powers VDD
and provides voltage for the output drivers.
FS0, FS1: Frequency select pins for determining the difference frequency between primary and secondary
pulses under normal operation. These pins can be hardwired to GND or VDD to get one of the available output
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.
4
UCC2751
UCC3751
APPLICATION INFORMATION
Power Stage Operation
transformer. Typical pulsewidth of the sampling signal is
280ns. As a result of sampling, the resultant output signal
matches the secondary voltage in amplitude and has a
low output frequency desired for ring generation.
The power stage used for the UCC3751 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 sinusoidal waveform across the transformer winding. The operation of this type of circuit is extensively covered in
Unitrode Application notes U-141 and U-148. Resonant
components CR1, CR2, LR, N should be chosen so that
the primary and secondary resonances are well
matched. Also, for the UCC3751 operation, switching frequency is fixed by crystal selection. So, the resonant
components must be selected to yield a resonant frequency close enough to the switching frequency to get a
low distortion sine-wave. Practically, since it is impossible 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 UCC3751. 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 differs from the primary switching frequency by the desired
output frequency (e.g. 20 Hz). The sampling is accomplished using a bi-directional switching circuit as shown
in Figure 2 and Figure 3. Figure 2 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. 3. The DRVS pin of
the UCC3751 provides the drive signal for the sampling
switch(es) and this signal is coupled through a pulse
The secondary winding of the power transformer also has
a tap (or a separate winding) to generate a loosely regulated DC voltage. This DC voltage can be used to offset
the ring generator output. The UCC3751 is also configured such that the AC output can go to zero under certain
conditions. Table 2 provides the logic levels for different
operating modes of UCC3751. Operation in mode 2 is
achieved by altering the sampling frequency to match the
switching frequency and sampling the secondary AC voltage at zero crossings. As a result, the resultant total output voltage between VOUT and GND is the semi-regulated
DC voltage achieved through the tapped secondary. This
feature allows the circuit to operate under off-hook and
idle conditions when only the DC portion of the voltage is
required. The activation of this mode occurs when the
OHD voltage exceeds a set threshold or RINGEN is low.
The incorporation of this mode eliminates any need for
external relays or switching circuits as well as eliminating
the need for an additional power supply for powering the
phone. The DC voltage level can be fine tuned by adjusting the voltage on the DELAY pin of the UCC3751. This
pin sets the sampling delay time during the off-hook
mode and allows a DC voltage to be developed between
V1 and VOUT during this mode. Fig. 1 illustrates the operation of this mode. When the DELAY is set between 0
and 1V, the sampling is done in phase with the primary
switching instances (at points A), leading to an average
voltage of 0V between V1 and VOUT for a sinusoidal secondary signal. If DELAY is set to another level, the sampling instance shifts (e.g. to point B) leading to an
effective voltage VB being developed between V1 and
VOUT. The actual VOUT is the sum of VB and the DC offset voltage derived from the additional (or tapped) winding (V1).
Table II. Operating mode selection.
Condition
Continuous Ringing
Idle (On Hook, No Ringing)
Low
Low
OHD
RINGEN
High
Low
Off-Hook
Cadenced Ringing
High
Low
X (Low/High)
High/Low
5
Sampling Output Mode
Frequency Offset from Primary (Mode 1)
Synchronized to Primary Frequency with Phase
Controlled by DELAY (Mode 2)
Mode 2
Mode 1/Mode 2
UCC2751
UCC3751
TRANSFORMER SECONDARY
VOLTAGE
VB
B
A
B
A
B
0
0 VDRV2
Figure 1. Effects of sampling delay during off-hook operation.
TO TRANSFORMER
TO TRANSFORMER
DRVS
DRVS
TO OUTPUT
TO OUTPUT
Figure 2. Sampling circuit with two FETs.
Figure 3. Sampling circuit with single FET and
full-bridge rectifier.
UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
6
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Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its products to the specifications applicable at the time of sale in accordance with
TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary
to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except
those mandated by government requirements.
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.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
products or services might be or are used. TI’s publication of information regarding any third party’s products
or services does not constitute TI’s approval, license, warranty or endorsement thereof.
Reproduction of information in TI data books or data sheets is permissible only if reproduction is without
alteration and is accompanied by all associated warranties, conditions, limitations and notices. Representation
or reproduction of this information with alteration voids all warranties provided for an associated TI product or
service, is an unfair and deceptive business practice, and TI is not responsible nor liable for any such use.
Resale of TI’s products or services with statements different from or beyond the parameters stated by TI for
that product or service voids all express and any implied warranties for the associated TI product or service,
is an unfair and deceptive business practice, and TI is not responsible nor liable for any such use.
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
Copyright  2001, Texas Instruments Incorporated
IMPORTANT NOTICE
Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its products to the specifications applicable at the time of sale in accordance with
TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary
to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except
those mandated by government requirements.
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.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
products or services might be or are used. TI’s publication of information regarding any third party’s products
or services does not constitute TI’s approval, license, warranty or endorsement thereof.
Reproduction of information in TI data books or data sheets is permissible only if reproduction is without
alteration and is accompanied by all associated warranties, conditions, limitations and notices. Representation
or reproduction of this information with alteration voids all warranties provided for an associated TI product or
service, is an unfair and deceptive business practice, and TI is not responsible nor liable for any such use.
Resale of TI’s products or services with statements different from or beyond the parameters stated by TI for
that product or service voids all express and any implied warranties for the associated TI product or service,
is an unfair and deceptive business practice, and TI is not responsible nor liable for any such use.
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
Copyright  2001, Texas Instruments Incorporated