ELANSC310 datasheet(86/119 Pages) AMD

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Élan™SC310 Microcontroller Data Sheet

PREL IMINARY

LOOP FILTERS

Each of the Phase-Locked Loops (PLLs) in the

ÉlanSC310 microcontroller requires an external Loop

Filter. Figure 30 describes each of the Loop Filters and

the recommended component values. The recom-

mended values for the components are shown in

Table 44.

The system designer shall include the pads on the

printed circuit board to accommodate the future instal-

lation/change of C2 and R1. This is recommended be-

cause the PLL performance can be affected by the

physical circuit board design. In addition, future revi-

sions of the ÉlanSC310 microcontroller with a modified

PLL design may require the addition of these compo-

nents to the system board.

The component value(s) of the Loop Filter directly af-

fect the acquisition (start up) time of the PLL circuit.

With the values recommended, the approximate acqui-

sition time is 200 ms. Therefore, the system designer

should program the Clock Control Register at Index 8F

appropriately. Bits 0, 1, and 2 set the PLL restart delay

time. When the PLLs are shut off for any reason (i.e.,

power management), the PLL will be allowed an

amount of time equal to that programmed in this regis-

ter to start up before the PLL outputs are enabled for

the internal device logic. A PLL restart delay time of

256 ms should be set in the Clock Control Register.

The pulse width of the RSTDRV signal is adjustable

based on the PLL start-up timing. For more informa-

tion, see the timing specifications in Table 45 on page

88, Figure 32–Figure 35.

Table 9 on page 28 shows the pin characteristics for the

Loop Filters, including the reset voltage level when

RESIN is active.

For more information about Loop Filters, see the

Trou-

bleshooting Guide for Micro Power Off Mode on

ÉlanTMSC300 and ÉlanSC310 Microcontrollers and

Evaluation Boards Application Note, order #21810.

Figure 30.

Loop-Filter Component

Notes:

When the PLL is on, VLFx should be approximately between

1 V and 2 V.

Table 44.

Loop-Filter Component Values

LFx

0.47

µF

Not Installed

0.47

µF

Not Installed

0.47

µF

Not Installed

0.47

µF

Not Installed

LFx

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