Programmable Maximum Duty Cycle PWM Controller

UCC1807-1/-2/-3
UCC2807-1/-2/-3
UCC3807-1/-2/-3

FEATURES

· User

Programmable

Maximum PWM
Duty Cycle

· 100

A Startup Current

Operation to 1MHz

Internal Full Cycle
Soft Start

Internal Leading Edge
Blanking of Current
Sense Signal

1 Amp Totem Pole
Output

DESCRIPTION

The UCC3807 family of high speed, low power integrated circuits contains all of the
control and drive circuitry required for off-line and DC-to-DC fixed frequency current
mode switching power supplies with minimal external parts count.

These devices are similar to the UCC3800 family, but with the added feature of a
user programmable maximum duty cycle. Oscillator frequency and maximum duty
cycle are programmed with two resistors and a capacitor. The UCC3807 family also
features internal full cycle soft start and internal leading edge blanking of the cur-
rent sense input.

The UCC3807 family offers a variety of package options, temperature range
options, and choice of critical voltage levels. The family has UVLO thresholds and
hysteresis levels for off-line and battery powered systems. Thresholds are shown in
the table below.

SLUS163 - JUNE 1997

BLOCK DIAGRAM

Part Number

Turn-on Threshold

Turn-off Threshold

UCCx807-1

7.2V

6.9V

UCCx807-2

12.5V

8.3V

UCCx807-3

4.3V

4.1V

UDG-95001-1

UCC1807-1/-2/-3
UCC2807-1/-2/-3
UCC3807-1/-2/-3

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (I

10mA) . . . . . . . . . . . . . . . . . . . . . . .13.5V

Supply Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30mA
OUT Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Analog Inputs (FB, CS) . . . . . . . . . . . . .

0.3V to (VDD + 0.3V)

Power Dissipation at T

C (N or J packages) . . . . . . . .1W

Power Dissipation at T

C (D package) . . . . . . . . . .0.65W

Storage Temperature . . . . . . . . . . . . . . . . . . . .

C to

150

Junction Temperature . . . . . . . . . . . . . . . . . . .

C to

150

Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . .+300

All currents are positive into, negative out of the specified terminal.
Consult Packaging Section of Databook for thermal limitations
and considerations of packages.

CONNECTION DIAGRAM

DIL-8, SOIC-8 (Top View)
J or N, D Packages

PARAMETER TEST

CONDITION

MIN

TYP

MAX

UNITS

Oscillator Section

Frequency

175

202

228

kHz

Temperature Stability

(Note 5)

2.5

Amplitude

(Note 1)

1/3

VDD

Error Amplifier Section

Input Voltage

COMP = 2.0V

1.95

2.00

2.05

Input Bias Current

Open Loop Voltage Gain

COMP Sink Current

FB = 2.2V, COMP = 1.0V

0.3

2.5

COMP Source Current

FB = 1.3V, COMP = 4.0V

0.2

0.5

PWM Section

Maximum Duty Cycle

Minimum Duty Cycle

COMP = 0V

Current Sense Section

Gain

(Note 2)

1.1

1.65

1.8

V/V

Maximum Input Signal

COMP = 5.0V (Note 3)

0.9

1.0

1.1

Input Bias Current

200

CS Blank Time

100

150

Overcurrent Threshold

1.4

1.5

1.6

COMP to CS Offset

CS = 0V

0.55

1.1

1.65

Output Section

OUT Low Level

I = 100mA

0.4

OUT High Level

I = 100mA, VDD

OUT

0.4

Rise / Fall Time

CL = 1nF (Note 5)

100

ELECTRICAL CHARACTERISTICS

Unless otherwise stated these specifications apply for T

C to

125

C for

UCC1807-1/-2/-3;

C to

C for UCC2807-1/-2/-3; and 0

C to

C for UCC3807-1/-2/-3; VDD = 10V (Note 6), R

= 12k

= 4.7k

, CT = 330pF, 1.0

F capacitor from VDD to GND, T

= T

ORDERING INFORMATION

UCC 807

UVLO Threshold
Package
Temperature Range

PARAMETER TEST

CONDITION

MIN

TYP

MAX

UNITS

Undervoltage Lockout Section

Start Threshold

UCCx807-1 (Note 4)

6.6

7.2

7.8

UCCx807-2

11.5

12.5

13.5

UCCx807-3

4.1

4.3

4.5

Minimum Operating Voltage After Start

UCCx807-1 (Note 4)

6.3

6.9

7.5

UCCx807-2

7.6

8.3

9.0

UCCx807-3

3.9

4.1

4.3

Hysteresis

UCCx807-1

0.1

0.3

0.5

UCCx807-2

3.5

4.2

5.1

UCCx807-3

0.1

0.2

0.3

Soft Start Section

COMP Rise Time

FB = 1.8V, From 0.5V to 4.0V

Overall Section

Startup Current

VDD < Start Threshold (UCCx807-1,-3)

0.1

0.2

VDD < Start Threshold (UCCx807-2)

0.15

0.25

Operating Supply Current

FB = 0V, CS = 0V, No Load (Note 7)

1.3

2.1

VDD Zener Shunt Voltage

= 10mA

12.0

13.5

15.0

Shunt to Start Difference

0.5

1.0

UCC1807-1/-2/-3
UCC2807-1/-2/-3
UCC3807-1/-2/-3

ELECTRICAL CHARACTERISTICS (cont.)

Unless otherwise stated these specifications apply for T

C to

125

C for UCC1807-1/-2/-3;

C to

C for UCC2807-1/-2/-3; and 0

C to

C for UCC3807-1/-2/-3; VDD = 10V (Note 6),

= 12k

, R

= 4.7k

, CT = 330pF, 1.0

F capacitor from VDD to GND, T

= T

Note 1: Measured at TRIG; signal minimum = 1/3 VDD, maximum = 2/3 VDD.

Note 2: Gain is defined by: A = , 0

0.8V

Note 3: Parameter measured at trip point of latch with FB at 0V.
Note 4: Start Threshold and Zener Shunt thresholds track one another.
Note 5: Guaranteed by design. Not 100% tested in production.
Note 6: Adjust VDD above the start threshold before setting at 10V for UCC3807-2.
Note 7: Does not include current in external timing RC network.

COMP: COMP is the output of the error amplifier and the
input of the PWM comparator. The error amplifier in the
UCC3807 is a low output impedance, 2MHz operational
amplifier. COMP can both source and sink current. The
error amplifier is internally current limited, which allows
zero duty cycle by externally forcing COMP to GND.

The UCC3807 family features built-in full cycle soft start.
Soft start is implemented as a clamp on the maximum
COMP voltage.

CS: Current sense input. There are two current sense
comparators on the chip, the PWM comparator and an
overcurrent comparator.

The UCC3807 also contains a leading edge blanking cir-
cuit, which disconnects the external CS signal from the
current sense comparator during the 100ns interval
immediately following the rising edge of the signal at the
OUT pin. In most applications, no analog filtering is
required on CS. Compared to an external RC filtering
technique, leading edge blanking provides a smaller
effective CS to OUT propagation delay. Note, however,
that the minimum non-zero on-time of the OUT signal is

directly affected by the leading edge blanking and the CS
to OUT propagation delay.

The overcurrent comparator is only intended for fault
sensing. Exceeding the overcurrent threshold causes a
soft start cycle.

FB: The inverting input to the error amplifier. For best
stability, keep connections to FB as short as possible
and stray capacitance as small as possible.

GND: Reference ground and power ground for all func-
tions of the part.

OUT: The output of a high current power driver capable
of driving the gate of a power MOSFET with peak cur-
rents exceeding 1A. OUT is actively held low when VDD
is below the UVLO threshold.

The high current power driver consists of MOSFET out-
put devices in a totem pole configuration. This allows the
output to switch from VDD to GND. The output stage also
provides a very low impedance which minimizes over-
shoot and undershoot. In most cases, external Schottky
clamp diodes are not required.

PIN DESCRIPTIONS

COMP

TRIG/DISCH: Oscillator control pins. TRIG is the oscilla-
tor timing input, which has an RC-type charge/discharge
signal controlling the chip's internal oscillator. DISCH is
the pin which provides the low impedance discharge
path for the external RC network during normal opera-
tion. Oscillator frequency and maximum duty cycle are
computed as follows:

frequency

duty cycle

as shown in Figure 1.

For best performance, keep the lead from C

to GND as

short as possible. A separate ground connection for C

desirable. The minimum value of R

is 10k

, the mini-

mum value of R

is 2.2k

, and the minimum value of C

is 47pF.

VDD: The power input connection for this device. Total
VDD current is the sum of quiescent current and the
average OUT current. Knowing the operating frequency
and the MOSFET gate charge (Qg), average OUT cur-
rent can be calculated from

OUT

= Qg

F, where F is frequency.

To prevent noise problems, bypass VDD to GND with a
ceramic capacitor as close to the chip as possible in par-
allel with an electrolytic capacitor.

UCC1807-1/-2/-3
UCC2807-1/-2/-3
UCC3807-1/-2/-3

Figure 1. Oscillator Block Diagram

+ R

+ 2R

1.4

+ 2R

PIN DESCRIPTIONS (cont.)

APPLICATIONS INFORMATION

The circuit shown in Figure 2 illustrates the use of the
UCC3807 in a typical off-line application. The 100W,
200kHz, universal input forward converter produces a
regulated 12VDC at 8 Amps. The programmable maxi-
mum duty cycle of the UCC3807 allows operation down
to 80VRMS and up to 265VRMS with a simple RCD
clamp to limit the MOSFET voltage and provide core
reset. In this application the maximum duty cycle is set to
about 65%. Another feature of the design is the use of a
flyback winding on the output filter choke for both boot-
strapping and voltage regulation. This method of loop
closure eliminates the optocoupler and secondary side
regulator, common to most off-line designs, while provid-
ing good line and load regulation.

T1:

Core:

Magnetics Inc. #P-42625-UG (ungapped)

Primary:

28 turns of 2x #26AWG

Secondary:

6 turns of 50x0.2mm Litz wire

L1:

Core:

Magnetics Inc. #P-42625-SG-37 (0.020" gap)

Main Winding:

13 turns of 2x #18AWG

Second Winding:11 turns of #26AWG

Magnetics Inc.

900 E. Butler Road
P.O. Box 391
Butler, PA 16003
Tel: (412) 282-8282
Fax: (412) 282-6955

UDG-95002-1

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 acknowledgement, including those
pertaining to warranty, patent infringement, and limitation of liability.

TI warrants performance of its semiconductor 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
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In order to minimize risks associated with the customer's applications, adequate design and operating
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TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
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party's products or services does not constitute TI's approval, warranty or endorsement thereof.

1999, 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.

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.

Mailing Address:

Texas Instruments
Post Office Box 655303
Dallas, Texas 75265

2001, Texas Instruments Incorporated

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