ELANSC310 AMD [Advanced Micro Devices], ELANSC310 Datasheet - Page 86

• Manufacturer Part Number: ELANSC310
• Description: Single-Chip, 32-Bit, PC/AT Microcontroller
• Manufacturer: AMD [Advanced Micro Devices]

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
Élan
Evaluation Boards Application Note , order #21810.
86
TM
SC300 and ÉlanSC310 Microcontrollers and
Élan™SC310 Microcontroller Data Sheet
P R E L I M I N A R Y
Notes:
When the PLL is on, V
1 V and 2 V.
LFx
LFx
1
2
3
4
Table 44. Loop-Filter Component Values
Figure 30. Loop-Filter Component
C
R
1
1
R
0
0
0
0
1
LFx
should be approximately between
0.47 F
0.47 F
0.47 F
0.47 F
C
1
Not Installed
Not Installed
Not Installed
Not Installed
C
2
C
2