UCC28C43: difference between UC2843 and UCC28C43

Hi user021864,
The following snip is taken from the UCC28C43 datasheet:
"The UCC28C4x and UCC38C4x series are an enhanced replacement with pin-to-pin compatibility to the bipolar
UC284x, UC384x, UC284xA, and UC384xA families. The new series offers improved performance when
compared to older bipolar devices and other competitive BiCMOS devices with similar functionality. These
improvements generally consist of tighter specification limits that are a subset of the older product ratings,
maintaining drop-in capability. In new designs, these improvements can reduce the component count or enhance
circuit performance when compared to the previously available devices."

In particular you will notice that the UCC28C43 parts can operate at higher frequency and draw about one fifth of the supply current of earlier bipolar parts. Please note that although these parts are intended to be drop in replacements it is not possible to say this will be true for all applications. In particular I would like to draw your attention to the difference in maximum supply voltage and the fact that the UCC28C43 device does not contain the zener clamp included UC2843 bipolar devices

"VDD is the power input connection for this device. In normal operation, power VDD through a current limiting
resistor. 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 on the input bias pin. Also, because no internal clamp is included in the device, the VDD pin
must be protected from external sources which could exceed the 20 V level. If containing the start-up and
bootstrap supply voltage from the auxiliary winding NA below 20 V under all line and load conditions can not be
achieved, use a zener protection diode from VDD to GND. Depending on the impedance and arrangement of the
bootstrap supply, this may require adding a resistor, RVDD, in series with the auxiliary winding to limit the current
into the zener as shown in Figure 20. Insure that over all tolerances and temperatures, the minimum zener
voltage is higher than the highest UVLO upper turnon threshold. To ensure against noise related problems, filter
VDD with a ceramic bypass capacitor to GND. The VDD pin must be decoupled as close to the GND pin as
possible."

I hope this answers your question.
Joe Leisten