The MAX33076-9E, a family of quad receivers, offer premium performance with a highly integrated, robust feature set of fault protection, common-mode range, and ESD protection. Whether used for point to point or multipoint bus receiver system, careful and sound design methodology need to be taken for optimal performance.
Place a small 0.1µF decoupling capacitor at the VCC pin. This capacitor acts like a local energy reservoir and helps filter out voltage spikes and pass DC component.
- Separate the solid ground and power planes for lowest impedance and inductance to minimize noise. This also helps get the best possible conduction and reduces external influences of EMI noise.
- Keep the PCB traces as short as possible between the receiver and the connector to minimize attenuation and reflection.
- Place the decoupling capacitor and termination resistor as close to the receiver as possible. This helps minimize parasitic capacitance.
- For signal integrity, route the receiver inputs away from the supply lines. Likewise, route the receiver outputs away from supply lines.
- For a multipoint bus, keep stub length to a minimum to avoid reflections on the line. The higher the data rate, the shorter the stub length. A good rule of thumb for maximum stub length is to keep it shorter than 1/10 the driver rise time per the following formula:
where
tr = the rise time of the driver
v = signal velocity as a percentage of c
c = speed of light (9.8 x 108 ft/s)
A conservative signal velocity of 40% is a good estimate for a standard FR4 substrate and 60% for the cable. For a more accurate calculation, look for the velocity factor in a cable data sheet, which is determined by the dielectric material of the cable.
It is recommended to use a twisted pair of 24AWG cables with an impedance between 100Ω and 130Ω, a capacitance less than 100pF per meter between conductors, and a capacitance less than 200pF per meter between conductors and cable shield. Shielded CAT5 or similar Ethernet cable can be used as well.