3
INDUSTRIAL TEMPERATURE RANGE
IDT5V9950
3.3V PROGRAMMABLE SKEW PLL CLOCK DRIVER TURBOCLOCK II
JR.
Output skew with respect to the REF input is adjustable to com-
pensate for PCB trace delays, backplane propagation delays or to
accommodate requirements for special timing relationships between
clocked components. Skew is selectable as a multiple of a time unit
(tU) which ranges from 625ps to 1.3ns (see Programmable Skew
Range and Resolution Table). There are nine skew configurations
available for each output pair. These configurations are chosen by
the nF1:0 control pins. In order to minimize the number of control
pins, 3-level inputs (HIGH-MID-LOW) are used, they are intended for
but not restricted to hard-wiring. Undriven 3-level inputs default to
the MID level. Where programmable skew is not a requirement, the
control pins can be left open for the zero skew default setting. The
Control Summary Table shows how to select specific skew taps by
using the nF1:0 control pins.
PROGRAMMABLE SKEW
EXTERNAL FEEDBACK
By providing external feedback, the IDT5V9950 gives users flex-
ibility 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.
NOTES:
1. The device may be operated outside recommended frequency ranges without damage, but functional operation is not guaranteed.
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 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 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.
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 ac-
curate responses to input frequency changes.
FS = LOW FS = MID FS = HIGH Comments
Timing Unit Calculation (tU) 1/(32 x FNOM) 1/(16 x FNOM) 1/(8 x FNOM)
VCO Frequency Range (FNOM)(1,2) 24 to 50MHz 48 to 100MHz 96 to 200MHz
Skew Adjustment Range(3)
Max Adjustment: ±7.8125ns ±7.8125ns ±7.8125ns ns
±67.5° ±135° ±270° Phase Degrees
±18.75% ±37.5% ±75% % of Cycle Time
Example 1, FNOM = 25MHz tU = 1.25ns — —
Example 2, FNOM = 37.5MHz tU = 0.833ns — —
Example 3, FNOM = 50MHz tU = 0.625ns tU = 1.25ns —
Example 4, FNOM = 75MHz — tU = 0.833ns —
Example 5, FNOM = 100MHz — tU = 0.625ns tU = 1.25ns
Example 6, FNOM = 150MHz — — tU = 0.833ns
Example 7, FNOM = 200MHz — — tU = 0.625ns
PROGRAMMABLE SKEW RANGE AND RESOLUTION TABLE