MPC9774
MOTOROLA TIMING SOLUTIONS6
APPLICATIONS INFORMATION
MPC9774 Configurations
Configuring the MPC9774 amounts to properly configuring
the internal dividers to produce the desired output
frequencies. The output frequency can be represented by
this formula:
÷
÷
÷
⋅ ÷
where f
REF
is the reference frequency of the selected input
clock source (CCLKO or CCLK1), M is the PLL feedback
divider and N is a output divider. M is configured by the
FSEL_FB[0:1] and N is individually configured for each
output bank by the FSEL_A, FSEL_B and FSEL_C inputs.
The reference frequency f
REF
and the selection of the
feedback-divider M is limited by the specified VCO frequency
range. f
REF
and M must be configured to match the VCO
frequency range of 200 to 500 MHz in order to achieve stable
PLL operation:
f
VCO,MIN
(f
REF
⋅ VCO_SEL ⋅ M) f
VCO,MAX
The PLL post-divider VCO_SEL is either a divide-by-two
or a divide-by-four and can be used to situate the VCO into
the specified frequency range. This divider is controlled by
the VCO_SEL pin. VCO_SEL effectively extends the usable
input frequency range while it has no effect on the output to
reference frequency ratio. The output frequency for each
bank can be derived from the VCO frequency and the output
divider:
f
QA[4:0]
= f
VCO
÷ (VCO_SEL ⋅ N
A
)
f
QB[4:0]
= f
VCO
÷ (VCO_SEL ⋅ N
B
)
f
QC[3:0]
= f
VCO
÷ (VCO_SEL ⋅ N
C
)
Table 9. MPC9774 Divider
Divider Function VCO_SEL Values
M PLL feedback
÷2 8, 12, 16, 24
FSEL_FB[0:1]
÷4 16, 24, 32, 48
N
A
Bank A Output
÷2 4, 8
Divider FSEL_A
÷4 8, 16
N
B
Bank B Output
÷2 4, 8
Divider FSEL_B
÷4 8, 16
N
C
Bank C Output
÷2 8, 12
Divider FSEL_C
÷4 16, 24
Table 9 shows the various PLL feedback and output
dividers. The output dividers for the three output banks allow
the user to configure the outputs into 1:1, 2:1, 3:2 and 3:2:1
frequency ratios. Figure 3 and Figure 4 display example
configurations for the MPC9774:
Figure 3. Example Configuration Figure 4. Example Configuration
MPC9774
MPC9774 example configuration (feedback of
QFB = 20.83 MHz, VCO_SEL = ÷2, M = 12, N
A
=
2, N
B
= 4, N
C
= 4, f
VCO
= 500 MHz).
Frequency range Min Max
Input 8.33 MHz 20.83 MHz
QA outputs 50 MHz 125 MHz
QB outputs 25 MHz 62.5 MHz
QC outputs 25 MHz 62.5 MHz
MPC9774
MPC9774 example configuration (feedback of
QFB = 25 MHz, VCO_SEL = ÷2, M = 8, N
A
= 2,
N
B
= 4, N
C
= 6, f
VCO
= 400 MHz).
Frequency range Min Max
Input 20 MHz 48 MHz
QA outputs 50 MHz 120 MHz
QB outputs 50 MHz 120 MHz
QC outputs 100 MHz 200 MHz
