11.1 Layout Guidelines

Proper PCB layout is extremely important in a high current, fast switching circuit to provide appropriate device operation and design robustness. The UCC27531-Q1 gate driver incorporates short propagation delays and powerful output stages capable of delivering large current peaks with very fast rise and fall times at the gate of power switch to facilitate voltage transitions very quickly. At higher VDD voltages, the peak current capability is even higher (2.5-A and 5-A peak current is at VDD = 18 V). Very high di/dt can cause unacceptable ringing if the trace lengths and impedances are not well controlled. The following circuit layout guidelines are strongly recommended when designing with these high-speed drivers.

• Locate the driver device as close as possible to power device in order to minimize the length of high-current traces between the driver Output pins and the gate of the power switch device.
• Locate the VDD bypass capacitors between VDD and GND as close as possible to the driver with minimal trace length to improve the noise filtering. These capacitors support high peak current being drawn from VDD during turn-on of power switch. The use of low inductance SMD components such as chip resistors and chip capacitors is highly recommended.
• The turn-on and turn-off current loop paths (driver device, power switch and VDD bypass capacitor) should be minimized as much as possible in order to keep the stray inductance to a minimum. High di/dt is established in these loops at two instances – during turn-on and turn-off transients, which induces significant voltage transients on the output pins of the driver device and gate of the power switch.
• Wherever possible, parallel the source and return traces of a current loop, taking advantage of flux cancellation
• Separate power traces and signal traces, such as output and input signals.
• Star-point grounding is a good way to minimize noise coupling from one current loop to another. The GND of the driver should be connected to the other circuit nodes such as source of power switch, ground of PWM controller etc at one, single point. The connected paths should be as short as possible to reduce inductance and be as wide as possible to reduce resistance.
• Use a ground plane to provide noise shielding. Fast rise and fall times at OUT may corrupt the input signals during transition. The ground plane must not be a conduction path for any current loop. Instead the ground plane must be connected to the star-point with one single trace to establish the ground potential. In addition to noise shielding, the ground plane can help in power dissipation as well.

11.2 Layout Example

Figure 31. UCC27531-Q1 Layout Example

11.3 Thermal Considerations

The useful range of a driver is greatly affected by the drive power requirements of the load and the thermal characteristics of the package. In order for a gate driver to be useful over a particular temperature range the package must allow for the efficient removal of the heat produced while keeping the junction temperature within rated limits. The thermal metrics for the driver package are summarized in the Thermal Information section of the datasheet. For detailed information regarding the thermal information table, please refer to the TI Application Note, Semiconductor and IC Package Thermal Metrics (SPRA953).