UCC28C40, UCC28C41, UCC28C42, UCC28C43, UCC28C44, UCC28C45

UCC38C40, UCC38C41, UCC38C42, UCC38C43, UCC38C44, UCC38C45

SLUS458E -- AUGUST 2001 -- REVISED OCTOBER 2010

9

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APPLICATION INFORMATION

precautions

The absolute maximum supply voltage is 20 V, including any transients that may be present. If this voltage is

exceeded, device damage is likely. This is in contrast to the predecessor bipolar devices, which could survive

up to 30 V. Thus, the supply pin should be decoupled as close to the ground pin as possible. Also, since no clamp

is included in the device, the supply pin should be protected from external sources which could exceed the 20 V

level.

Careful layout of the printed board has always been a necessity for high frequency power supplies. As the device

switching speeds and operating frequencies increase the layout of the converter becomes increasingly

important.

This 8-pin device has only a single ground for the logic and power connections. This forces the gate drive current

pulses to flow through the same ground that the control circuit uses for reference. Thus, the interconnect

inductance should be minimized as much as possible. One implication is to place the device (gate driver)

circuitry close to the MOSFET it is driving. Note that this can conflict with the need for the error amplifier and

the feedback path to be away from the noise generating components.

circuit applications

Figure 4 shows a typical off-line application.

UDG--01071

C53

1COMP

2FB

3CS

4RT/CT

8

REF

7

VCC

6

OUT

5

GND

UCC38C44

R6

C13

R16

T1

R12

C5

C12

D50

C52

D51

C3

R10

R11

C18

C1A

F1

BR1

+

RT1

L50

C54

R55

R53

R56

C55

R52

SEC

COMMON

12 V

OUT

R50

C50

C51

R50

IC3

R54

AR

K

Q1

5V

OUT

AC INPUT

100 Vac -- 240 Vac

EMI FILTER

REQUIRED

D2

D6

IC2

IC2

Figure 4. Typical Off-Line Application

Figure 5 shows the forward converter with synchronous rectification. This application provides 48 V to 3.3 V at

10 A with over 85% efficiency and uses the UCC38C42 as the secondary-side controller and UCC3961 as the

primary-side startup control device.