SLUSC18A September 2014 – March 2015 UCC29950
The UCC29950 should be operated from a VCC rail which is within the limits given in the VCC Bias Supply section of the Electrical Characteristics table. To avoid the possibility that the device might stop switching, VCC must not be allowed to fall into the UVLO range. In order to minimize power dissipation in the device, VCC should not be unnecessarily high. Keeping VCC at 12 V is a good compromise between these competing constraints. The gate drive outputs from the UCC29950 deliver large current pulses into their loads. This indicates the need for a low ESR decoupling capacitor to be connected as directly as possible between the VCC and PGND terminals. Ceramic capacitors with a stable dielectric characteristic over temperature, such as X7R, are recommended. Avoid capacitors which have a large drop in capacitance with applied DC voltage bias and use a part that has a low voltage co-efficient of capacitance. The recommended decoupling capacitance is 10 µF, X7R, with at least a 25-V rating.
Operation in Self Bias Mode requires an additional, larger, energy storage capacitor. The value required depends on the details of the application but typically this part is between 100 µF and 300 µF. This energy storage capacitor does not require low ESR and it does not need to be placed close to the UCC29950. A 25-V rated aluminum electrolytic capacitor is a good choice.