Datasheet

Table Of Contents
Section 21 Clock Pulse Generator
REJ09B0140-0900 Rev. 9.00 Page 677 of 846
Sep 16, 2010
H8S/2215 Group
21.7 PLL Circuit for USB
The PLL circuit has the function of tripling or doubling* the 16- or 24-MHz* clock from the
system oscillator to generate the 48-MHz USB operating clock. When the PLL circuit is used, set
the UCKS3 to UCKS0 bits of UCTLR. For details, refer to section 15, Universal Serial Bus
Interface (USB). When the PLL circuit is not used, connect the PLLVCC pin to VCC, and leave
the PLLCAP pin open as shown in figure 21.11.
Note: * Available only in H8S/2215R, H8S/2215T and H8S/2215C.
16 MHz or
24 MHz
*
2
crystal
resonator
or ceramic
resonator
or external
clock
48-MHz
crystal
resonator
or external
clock
Open
Open
state
(2) PLL is not used(1) PLL is used
Notes: 1. CB, CPB is laminated ceramic.
2. The 24-MHz crystal resonator or external clock is available only in H8S/2215R, H8S/2215T and H8S/2215C.
R
P
:
200 Ω
PLLVCC
EXTAL
XTAL
EXTAL48
XTAL48
PLLCAP
PLLVSS
VCC
VSS
Vcc
C1: 470 pF
CPB: 0.1 μF
*
1
CB: 0.1 μF
*
1
R1: 3 kΩ
PLLVCC
EXTAL
XTAL
EXTAL48
XTAL48
PLLCAP
PLLVSS
VCC
VSS
Vcc
Crystal resonator or
external clock in range
13 MHz to 16 MHz for
H8S/2215, 13 MHz to
24 MHz for
H8S/2215R, and 16
MHz to 24 MHz for
H8S/2215C; 16 MHz or
24 MHz ceramic
resonator or external
clock for H8S/2215T
Figure 21.11 Example of PLL Circuit
When designing the board, place the capacitor C1 and resistor R1 as close as possible to the
PLLCAP pin. Other signal lines should be routed away from the oscillator circuit to prevent
induction from interfering with correct oscillation. C1 must be grounded to PLLVSS. In addition,
PLLVCC and PLLVSS must be separated from the VCC and VSS pins. Bypass capacitors CPB
and CB must be connected between VCC and VSS and between PLVCC and PLVSS,
respectively.