AN3213 datasheet(42/64 Pages) STMICROELECTRONICS

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ST7570 demonstration board description

AN3213

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Doc ID 17429 Rev 1

Another important parameter for effective heat dissipation is the copper thickness for both

top and bottom layers. 1 oz copper is considered as the minimum value to ensure good

dissipation.

The bottom-side routing plays an important role too. The solid ground area of copper under

the device must be as large as possible to minimize the thermal impedance. Therefore,

traces on the bottom-side must run as far as possible from the device area.

7.3.2

Ground connections

Good soldering of the ST7570 exposed pad is also required to minimize ground noise.

Being the exposed pad connected to VSSA, its cleanliness is directly related to the noise

level detected by the receiving circuitry (i.e. to the actual sensitivity level) and to the PLL

behavior.

It is very important to filter each supply to its respective ground: VCC to VSS, VCCA and

VDD_PLL to VSSA, VDDIO and VDD to GND.

7.3.3

Oscillator

It is very important to keep the crystal oscillator and the load capacitors as close as possible

to the device.

The resonant circuit must be far away from noise sources such as:

●

Power supply circuitry

●

Burst and surge protections

●

Mains coupling circuits

●

Any PCB track or via carrying an RF switching signal.

To properly shield and separate the oscillator section from the rest of the board, it is

recommended to use a ground plane, on both sides of the PCB, filling all the area below the

crystal oscillator. No tracks or vias, except for the crystal connections, should cross the

ground plane.

Figure 36.

PCB copper dissipating area on top

layer for the ST7570 demonstration

board

Figure 37.

PCB copper dissipating area on

bottom layer for the ST7570

demonstration board

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