Intel 386 manual Sx/1

PHYSICAL DESIGN AND DEBUGGING

	sx/1		5V Trace
IV		I	x/1	S
	?I		?\	I
	/	I	/	I
		"GND		i,U
	//		/'	GND
	?\"	I	7'\'<	I
	I	I	/	I
		r-,		r, =s
		GND		GND
	/ . --		//

Return or . / ,GNDTrace

	7'1'<		X	I
		I	7'1
/
		I	/ ,	I	S"
		I,		I,

	GND	GND
~	l./II 5V	--.A 5V

231732i11-3

Figure 11-3. Orthogonal Arrangement

systems. This capacitor is typically placed at the supply's entry point to the board. It should be an aluminum or'tantalum-electrolytic type capacitor having a low equivalent series capacitance and low equivalent series inductance. The capacitance value is typi- callylO to 47 JlF. An additional 0.1 JlF capacitor may be needed if supply noise is still a problem.

A second type of decoupling is used for the rest of the ICs on the board. Additional decoupling capacitors can be used across the devices between Vee and Vss lines. The voltage spikes that occur due to switching of gates are reduced because the extra current required during switching is supplied by the decoupling capacitors. These capacitors should be placed close to their devices since the -inductance of lengthier connection traces reduce their effectiveness.

11-6