AM3871 datasheet(174/345 Pages) TI1

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1.5 V (DVDD_DDR[x])

CVDD, CVDD_x

3.3 V Supplies

(DVDD, DVDD_x,

DVDD_C, VDDA_x_3P3)

1.8 V Supplies

(DVDD, DVDD_x, DVDD_M,

DVDD_DDR[x], VDDA_x_1P8, VDDA_1P8)

AM3874, AM3872, AM3871

SPRS695

– SEPTEMBER 2011

www.ti.com

Figure 7-3. Power-Down Sequence

7.2.9

Power-Supply Decoupling

7.2.9.1

Analog and PLL

PLL and Analog supplies benefit from filters or ferrite beads to keep the noise from causing problems. The

minimum recommendation is a ferrite bead along with at least one capacitor on the device side of the

bead. An additional recommendation is to add one capacitor just before the bead to form a Pi filter. The

filter needs to be as close as possible to the device pin, with the device side capacitor being the most

important component to be close to the device pin. PLL pins close together can be combined on the same

supply, but analog pins should all have their own filters. PLL pins farther away from each other may need

their own filtered supply.

7.2.9.2

Digital

Recommended capacitors for power supply decoupling are all 0.1uF in the smallest body size that can be

used. Capacitors are more effective in the smallest physical size to limit lead inductance. For example,

0201 sized capacitors are better than 0402 sized capacitors, and so on. TI recommends using capacitors

no larger than 0402. Place at least one capacitor for every two power pins. For those power pins that have

only one pin, a capacitor is still required. Place one bulk (10 uF or larger) capacitor for every 10 or so

power pins as closely as possible to the chip. These larger caps do not need to be under the chip

footprint.

Pay special attention not to put so much capacitance on the supply that it slows the start-up voltage ramp

enough to change the power sequencing order. Also be sure to verify that the main chip reset is low until

after all supplies are at their correct voltage and stable.

DDR peripheral related supply capacitor numbers are provided in Section 8.13, LPDDR/DDR2/DDR3

Memory Controller.

174

Power, Reset, Clocking, and Interrupts

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