A proper layout is critical for the operation of
any switched mode power supply, especially at high switching frequencies. Therefore,
the PCB layout of the TPSM8287Axx demands careful attention to make sure of best
performance. A poor layout can lead to issues like the following:
- Bad line and load regulation
- Instability
- Increased EMI radiation
- Noise sensitivity
Refer to the Five Steps to a Great PCB Layout for
a Step-Down Converter analog design journal for a detailed
discussion of general best practices. The following are specific recommendations for
the TPSM8287Axx:
- Place the input capacitors as close as possible
to the VIN and GND pins of the device. This placement is the most critical
component placement. Route the input capacitors directly to the VIN and GND pins
avoiding vias.
- Place the output capacitors close to the VOUT and
GND pins and route them directly avoiding vias.
- Place the IC close to the load to minimize the
power loss from voltage drop on the output and to minimize parasitic inductance
between the output capacitors at the TPSM8287Axx and those at the load.
- Use GND vias under the three exposed thermal pads
to improve thermal performance. Directly connect the GND pins to the exposed
thermal pad with copper on the top PCB layer.
- Route the VOSNS and GOSNS remote sense lines as a
differential pair and connect them to the lowest impedance point at the load. Do
not route the VOSNS and GOSNS traces close to any switch nodes, the input
capacitors, clock signals, or other aggressor signals.
- Connect the compensation components between COMP
and GOSNS. Do not connect the compensation components directly to power
ground.
- Place the VSETx resistors (and SYNC_OUT resistor
in the secondary devices) close to the TPSM8287Axx to minimize parasitic
capacitance.
- Route VOSNS, GOSNS, and COMP directly to keep
them short and avoid noisy aggressor signals in the stacked configuration.
- Refer to Figure 9-57 for an
example of component placement, routing, and thermal design.
- See the recommended land pattern for the
TPSM8287Axx at the end of this data sheet. For best manufacturing results,
create the pads as solder mask defined (SMD) when some pins (such as VIN, VOUT,
and GND) are connected to large copper planes. Using SMD pads keeps each pad the
same size and avoids solder pulling the device during reflow.