Designers must pay close attention to PCB layout to achieve optimum performance for the UCC23511. Some key guidelines are:
- Component placement:
- Low-ESR and low-ESL capacitors must be connected close to the device between the VCC and VEE pins to bypass noise and to support high peak currents when turning on the external power transistor.
- To avoid large negative transients on the VEE pins connected to the switch node, the parasitic inductances between the source of the top transistor and the source of the bottom transistor must be minimized.
- Grounding considerations:
- Limiting the high peak currents that charge and discharge the transistor gates to a minimal physical area is essential. This limitation decreases the loop inductance and minimizes noise on the gate terminals of the transistors. The gate driver must be placed as close as possible to the transistors.
- High-voltage considerations:
- To ensure isolation performance between the primary and secondary side, avoid placing any PCB traces or copper below the driver device. A PCB cutout or groove is recommended in order to prevent contamination that may compromise the isolation performance.
- Thermal considerations:
- A large amount of power may be dissipated by the UCC23511 if the driving voltage is high, the load is heavy, or the switching frequency is high. Proper PCB layout can help dissipate heat from the device to the PCB and minimize junction-to-board thermal impedance (θJB).
- Increasing the PCB copper connecting to the VCC and VEE pins is recommended, with priority on maximizing the connection to VEE. However, the previously mentioned high-voltage PCB considerations must be maintained.
- If the system has multiple layers, TI also recommends connecting the VCC and VEE pins to internal ground or power planes through multiple vias of adequate size. These vias should be located close to the IC pins to maximize thermal conductivity. However, keep in mind that no traces or coppers from different high voltage planes are overlapping.