IDT5V9885B Integrated Device Technology, Inc., IDT5V9885B Datasheet - Page 7

• Manufacturer Part Number: IDT5V9885B
• Description: 3.3V EEPROM PROGRAMMABLE CLOCK GENERATOR
• Manufacturer: Integrated Device Technology, Inc.

Feedback-Divider
for either PLL0 or PLL1, then the SS_OFFSET[5:0] bits (0x61, 0x69) would be factored into the overall feedback divider value. See the SPREAD SPECTRUM
GENERATION section for more details on how to configure PLL0 and PLL1 when spread spectrum is enabled. The two PLLs can also be configured for fractional
divide ratios. See FRACTIONAL DIVIDER for more details. For PLL2, only the N[11:0] bits (N2) are used to program its feedback divider and there is no spread
spectrum generation and fractional divides capability. The12-bit feedback-divider integer values range from 1 to 4095.
PLL0 and PLL1:
M = 2*N[11:0] + A[3:0] + 1 + SS_OFFSET[5:0] * 1/64
M = 2*N[11:0] + A[3:0] + 1 (spread spectrum disabled)
A[3:0] = 0000 = -1
Note: A[3:0] < (N[11:0] - 5), must be met when using A. N cannot be programmed with a value of 4, 8, or 16 when using A.
PLL2:
M = N[11:0]
A fractional divide can also be set for PLL0 and PLL1 by using the A[3:0] bits in conjunction with the SS_OFFSET[5:0] bits, which is detailed in the FRACTIONAL
DIVIDER section. Note that the VCO has a frequency range of 10MHz to 1200MHz. To maintain low jitter, it is best to maximize the VCO frequency. For example,
if the reference clock is 100MHz and a 200MHz clock is required, to achieve the best jitter performance, multiply the 100MHz by 12 to get the VCO running at
the highest possible frequency of 1200MHz and then divide it down to get 200MHz. Or if the reference clock is 25MHz and 20MHz is the required clock, multiply
the 25MHz by 40 to get the VCO running at 1000MHz and then divide it down to get 20MHz. If N is set to '0x00', the VCO will slew to the minimum frequency.
Post-Divider
divide along its path. The 10-bit post-dividers will divide down the output banks' frequency with integer values ranging from 1 to 1023.
except for OUT1, has a set of PM bits. When disabling the post-divider, no clock will appear at the outputs, but will remain powered on. The values are listed
in the table below.
IDT5V9885B
3.3V EEPROM PROGRAMMABLE CLOCK GENERATOR
N[11:0] and A[3:0] are the bits used to program the feedback-divider for PLL0 (N0 and A0) and PLL1 (N1 and A1). If spread spectrum generation is enabled
The following equations govern how the feedback divider value is set. Note that the equations are different for PLL0/PLL1 and PLL2
The user can achieve an even or odd integer divide ratio for both PLL0 and PLL1 by setting the A[3:0] bits accordingly and disabling the spread spectrum.
Q[9:0] are the bits used to program the 10-bit post-dividers on output banks OUT2-6. OUT1 bank does not have a 10-bit post-divider or any other post-
There is the option to choose between disabling the post-divider, utilizing a div/1, a div/2, or the 10-bit post-divider by using the PM[1:0] bits. Each bank,
= 0001 = 1
= 0010 = 2
= 0011 = 3
= 1111 = 15
.
.
.
PM[1:0]
00
01
10
11
(Eq. 5)
Q[9:0] + 2 (Eq. 6)
P Post-Divider
disabled
div/1
div/2
(Eq. 3)
(Eq. 4)
7
VCO
Post-Divider Diagram
/ (Q+2)
P
INDUSTRIAL TEMPERATURE RANGE
/2
00
01
10
11
PM[1:0]
/2
To Outputs