April 1999

®

TOP412/414

TOPSwitch Family

Three-terminal DC to DC PWM Switch

®

Product Highlights

Low Cost Replacement for Discrete Switchers

• Up to 15 fewer components - cuts cost, increases reliability

• Allows for a smaller and lighter solution under 12 mm

height, all surface mount components

Over 80% Efficiency in Flyback Topology

• Built-in start-up and current limit reduce DC losses

• Low capacitance MOSFET cuts switching losses

•CMOS controller/gate driver consumes only 7 mW

• 70% maximum duty cycle minimizes conduction losses

Simplifies Design - Reduces Time to Market

• Integrated PWM Controller and high power MOSFET

• Only one external capacitor needed for compensation,

bypass and start-up/auto-restart functions

System Level Fault Protection Features

• Auto-restart and cycle by cycle current limiting functions

handle both primary and secondary faults

• On-chip latching thermal shutdown protects the entire

system against overload

Highly Versatile

• Implements Buck, Boost, Flyback or Forward topology

• Easily interfaces with both opto and primary feedback

• Supports continuous or discontinuous mode of operation

• Specified for operation down to 16 V DC input

Description

The TOPSwitch family implements, with only three terminals,

all functions necessary for a DC to DC, converter: high voltage

N-channel power MOSFET with controlled turn-on gate driver,

voltage mode PWM controller with integrated 120 kHz oscillator,

high voltage start-up bias circuit, bandgap derived reference,

bias shunt regulator/error amplifier for loop compensation and

fault protection circuitry. Compared to discrete MOSFET and

controller or self oscillating (RCC) switching converter solutions,

a TOPSwitch integrated circuit can reduce total cost, component

count, size, weight and at the same time increase efficiency and

system reliability.

This device is well suited for Telecom,

Cablecom and other DC to DC converter applications up to

Figure 1. Typical Application.

MINIMUM

INPUT

VOLTAGE

ORDER PART NUMBER

18 VDC

3 W

9 W

TOP412G

TOP414G

24 VDC

36 VDC

48 VDC

60 VDC

72 VDC

90 VDC

12 W

Table 1. TOP412/414 Output Power.

4 W

5 W

6 W

7 W

9 W

18 W

21 W

12 W

15 W

15 W

18 W

Notes: 1. Assumes maximum junction temperature of 100

°C

2. Assumes output of 5 V and K

power capability in a given application depends on thermal

environment,transformerdesign,efficiencyrequired,inputstorage

capacity, etc.

PI-2371-120198

D

S

C

CONTROL

TOP414

VIN

VO

21 W of output power.

Internally, the lead frame of the

SMD-8 package uses six of its pins to transfer heat from the chip

directly to the board, eliminating the cost of a heat sink.