January 1999 TOKO, Inc.

Page 1

TK75001

OSCILLATOR

FB

CT

ICHG

205 µA

fCLK

TQ

TOGGLE FF

SLOPE

COMPENSATION

1.35 V

PWM LATCH

DRV

CURRENT

CONTROL

DETECTOR

OVERCURRENT

DETECTOR

GND

BANDGAP

REFERENCE

UVLO

14.5 V

10.5 V

VCC

S

R

Q

IFR

146 µA

ICT

FREQUENCY

REDUCTION

LATCH

17.5 V

0.98 V

S

Q

R

IDS

2 mA

APPLICATIONS

s Off-Line Power Supplies

s Industrial Power Supplies

s Telecom Power Supplies

s Off-Line Battery Chargers

FEATURES

s Optimized for Off-Line Operation

s Maximum Duty Ratio 44% (typ.)

s Maximum Clock Frequency Above 1 MHz

s Frequency Reduction for Improved Overcurrent

Protection

s Low Standby Current for Current-Fed Start-Up

s Current-Mode or Voltage-Mode Control

s Internal User-Adjustable Slope Compensation

s Functionally Integrated & Simplified 5-pin Design

TK75001

BLOCK DIAGRAM

DESCRIPTION

The TK75001 is a simplified primary side controller

optimized for off-line switching power supplies. It is suitable

for both voltage-mode and current-mode control and has

advanced features not available in controllers with a higher

pin count. The key to full functionality in a 5-pin design is

that the current signal and the error signal are added

together and fed into the feedback pin. A sawtooth current

flowing out of the feedback pin provides a slope

compensation ramp (in current-mode applications) or a

PWM ramp (in voltage-mode applications), in proportion to

the resistance terminating that pin. If the sum of the current

sense signal, error signal and ramp signal exceeds the

Overcurrent Detector threshold indicating that the Current

Control Detector has lost control of the switch current, the

charging current of the timing capacitor will be reduced to

about 25% for the remainder of the clock period. The

reduced charging current causes no more than a one-third

reduction in switching frequency, effectively preventing

short-circuit current runaway.

The TK75001 is available in an 8-pin DIP package.

ORDERING INFORMATION

TAPE/REEL CODE

MG: Magazine

Tape/Reel Code

TK75001D

Temperature Code

TEMP. CODE (OPTIONAL)

I: -40 to +85 C

75001

GND

DRV

NC

VCC

GND

NC

FB

CT

Note: Pins 2 and 3 must be externally

connected for proper operation.

PWM CONTROLLER