Performance Motion Devices Juno MC71112, Руководство пользователя

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Application Notes — MC74113 & MC75113
96
Juno Step Motor Control IC User Guide
15
15.4 Clock Generator, Grounding and
Decoupling
15.4.1 Grounding and Decoupling
As shown in Figure 15-2 , each of the digital supply voltage pins should be connected to the +3.3 Vcc. A minimum of
1.2 μ F capacitor should be used to decouple each Vcc pin. A 2.2 μ F ceramic capacitor is recommended. If the +3.3 Vcc
source is noisy, additional ferrite bead can be placed in series with the decoupling cap to form a LC filtering network
on the power pin.
Each of the “FltCap” pins should be connected to a minimum of 1.2 μ F filtering capacitor which in turn connects to
ground. A 2.2 μ F ceramic capacitor is used in the schematic. The filtering capacitors must be placed as close as possible
to each one of the “FltCap” pins. This general rule applies to all analog and digital components, although in some of
the schematics that follow these capacitors are not shown for reasons of brevity. In some cases, especially for analog
processing circuitry, it may be beneficial to run a separate power line from the power supply to the component in order
to prevent power supply fluctuations from impacting low-level signal components.
The same points should be considered when designing the ground. A good board layout practice should have a star
connection at one point in the power supply.
Additional filtering, such as ferrite beads, may be inserted between the analog and digital grounds to suppress high
frequency ground noise. Some components, such as motor drivers, require special grounding. The system designer
should refer to the component data sheets of selected components in order to ensure correct usage of the grounding
methods.
15.4.2 Decoupling of the On-chip ADC
The voltage supply to the ADC should be decoupled with a 2.2 μ F ceramic capacitor (typical) on the pin. It should be
placed as close as possible to the ADC power supply input pins.