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
Output Power Capability
1-4
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
RP
of 0.4 3. Soldered to 1 sq. inch
(645 mm
2
), 2 oz. copper clad (610 gm/mm
2
) 4. The continuous
power capability in a given application depends on thermal
environment, transformer design, efficiency required, input storage
capacity, etc.
PI-2371-120198
D
S
C
CONTROL
TOP414
V
IN
V
O
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.
