Figure 11-1 shows the recommended placement and routing of device
bypass capacitors. Below guidelines must be followed to achieve low emissions design:
- High frequency bypass capacitors 10 nF must be placed close to VDD
and VISOOUT pins, within 1 mm distance away from device pins. This is very
essential for optimised radiated emissions performance. Ensure that these capacitors are
0402 size so that they offer least inductance (ESL).
- Bulk capacitors of atleast 10 μF must be placed on power converter input
(VDD) and output (VISOOUT) supply pins after the 10 nF capacitor
with a distance of 2 - 4 mm, as shown in Layout Example.
- Traces on VDD and GND1 must be symmetric till bypass
capacitors. Similarly traces on VISOOUT and GND2 must be symmetric.
- Place two 0402 size Ferrite beads (Part number: BLM15EX331SN1) on
power supply pins, one between VISOOUT and VISOIN and the other
between GND2 (pin 11) and GND2(pin 15), as shown in example PCB layout, so that any high
frequency noise from power converter output sees a high impedance before it goes to
other components on PCB.
- Do not have any metal traces or ground pour within 4 mm of power converter
output terminals VISOOUT (pin12) and GND2 (pin11).
- Place the CAN BUS protection and filtering circuitry close to the bus
connector to prevent transients, ESD, and noise from propagating onto the board. This
layout example shows an optional transient voltage suppression (TVS) diode, D1, which
may be implemented if the system-level requirements exceed the specified rating of the
transceiver. This example also shows two optional 68pF bus filter capacitors
- Common mode choke or ferrite beads on bus terminals (CANH/CANL) can minimise
any high frequency noise that can couple of CAN bus cable which can act as antenna and
amplify that noise. This will improve Radiated emissions performance on a system
level.
- Following the layout guidelines of EVM as much as possible is highly
recommended for a low radiated emissions design. EVM Link is available in Related Documentation.