IDT5993A Datasheet, PDF (3/8 Pages) Integrated Device Technology – PROGRAMMABLE SKEW PLL CLOCK DRIVER TURBOCLOCK

IDT5993A
PROGRAMMABLE SKEW PLL CLOCK DRIVER TURBOCLOCK
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
EXTERNAL FEEDBACK
By providing external feedback, the IDT5993A gives users flexibility
with regard to skew adjustment. The FB signal is compared with the
input REF signal at the phase detector in order to drive the VCO. Phase
differences cause the VCO of the PLL to adjust upwards or downwards
accordingly.
An internal loop filter moderates the response of the VCO to the
phase detector. The loop filter transfer function has been chosen to
provide minimal jitter (or frequency variation) while still providing accu-
rate responses to input frequency changes.
PLL PROGRAMMABLE SKEW RANGE AND RESOLUTION TABLE
FS = LOW
FS = MID
FS = HIGH
Comments
Timing Unit Calculation (tU)
VCO Frequency Range (FNOM)^(1,2)
Skew Adjustment Range⁽³⁾
1/(44 x FNOM)
15 to 35MHz
1/(26 x FNOM)
25 to 60MHz
1/(16 x FNOM)
40 to 100 MHz
Max Adjustment:
±9.09ns
±9.23ns
±9.38ns
ns
±49°
±83°
±135°
Phase Degrees
±14%
±23%
±37%
% of Cycle Time
Example 1, FNOM = 15MHz
tU = 1.52ns
—
—
Example 2, FNOM = 25MHz
tU = 0.91ns
tU = 1.54ns
—
Example 3, FNOM = 30MHz
tU = 0.76ns
tU = 1.28ns
—
Example 4, FNOM = 40MHz
—
tU = 0.96ns
tU = 1.56ns
Example 5, FNOM = 50MHz
—
tU = 0.77ns
tU = 1.25ns
Example 6, FNOM = 80MHz
—
—
tU = 0.78ns
NOTES:
1. The device may be operated outside recommended frequency ranges without damage, but functional operation is not guaranteed. Selecting the appropriate FS value based on
input frequency range allows the PLL to operate in its ‘sweet spot’ where jitter is lowest.
2. The level to be set on FS is determined by the nominal operating frequency of the VCO and Time Unit Generator. The VCO frequency always appears at 1Q1:0, 2Q1:0, and the
higher outputs when they are operated in their undivided modes. The frequency appearing at the REF and FB inputs will be the same as the VCO when the output connected
to FB is undivided. The frequency of the REF and FB inputs will be 1/2 or 1/4 the VCO frequency when the part is configured for a frequency multiplication by using a divided
output as the FB input.
3. Skew adjustment range assumes that a zero skew output is used for feedback. If a skewed Q output is used for feedback, then adjustment range will be greater. For example
if a 4tU skewed output is used for feedback, all other outputs will be skewed –4tU in addition to whatever skew value is programmed for those outputs. ‘Max adjustment’ range
applies to output pairs 3 and 4 where ± 6tU skew adjustment is possible and at the lowest FNOM value.
CONTROL SUMMARY TABLE FOR FEEDBACK SIGNALS
nF1:0
LL⁽¹⁾
Skew (Pair #1, #2)
–4tU
LM
–3tU
LH
–2tU
ML
–1tU
MM
Zero Skew
MH
1tU
HL
2tU
HM
3tU
HH
4tU
NOTE:
1. LL disables outputs if TEST = MID and GND/sOE = HIGH.
Skew (Pair #3)
Divide by 2
–6tU
–4tU
–2tU
Zero Skew
2tU
4tU
6tU
Divide by 4
3