UCC28C40, UCC28C41, UCC28C42, UCC28C43, UCC28C44, UCC28C45
UCC38C40, UCC38C41, UCC38C42, UCC38C43, UCC38C44, UCC38C45
SLUS458E -- AUGUST 2001 -- REVISED OCTOBER 2010
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
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
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.
Figure 4 shows a typical off-line application.
100 Vac -- 240 Vac
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.