The performance of the switching regulator depends as much on the layout of the PCB as the component selection. Following a few simple guidelines will maximize noise rejection and minimize the generation of EMI within the circuit.
Discontinuous currents are the most likely to generate EMI. Therefore, take care when routing these paths. The main path for discontinuous current in the devices using a buck regulator topology contains the input capacitor, CIN, the recirculating diode, D, the N-channel MOSFET, Q1, and the sense resistor, RIS. In the TPS92692 and TPS92692-Q1 devices using a boost regulator topology, the discontinuous current flows through the output capacitor COUT, diode, D, N-channel MOSFET, Q1, and the current sense resistor, RIS. In devices using a buck-boost regulator topolog. Be careful when laying out both discontinuous loops. Ensure that these loops are as small as possible. In order to minimize parasitic inductance, ensure that the connection between all the components are short and thick. In particular, make the switch node (where L, D, and Q1 connect) just large enough to connect the components. To minimize excessive heating, large copper pours can be placed adjacent to the short current path of the switch node.
Route the CSP and CSN together with Kelvin connections to the current sense resistor with traces as short as possible. If needed, use common mode and differential mode noise filters to attenuate switching and diode reverse recovery noise from affecting the internal current sense amplifier.
Because the COMP, IS, OV, DIM/PWM, and IADJ pins are all high-impedance inputs that couple external noise easily, ensure that the loops containing these nodes are minimized whenever possible.
In some applications, the LED or LED array can be far away from the TPS92692 and TPS92692-Q1 devices, or on a separate PCB connected by a wiring harness. When an output capacitor is used and the LED array is large or separated from the rest of the regulator, place the output capacitor close to the LEDs to reduce the effects of parasitic inductance on the AC impedance of the capacitor.
The TPS92692 and TPS92692-Q1 devices have an exposed thermal pad to aid power dissipation. Adding several vias under the exposed pad helps conduct heat away from the device. The junction-to-ambient thermal resistance varies with application. The most significant variables are the area of copper in the PCB and the number of vias under the exposed pad. The integrity of the solder connection from the device exposed pad to the PCB is critical. Excessive voids greatly decrease the thermal dissipation capacity.