ICD2051 Cypress Semiconductor Corp., ICD2051 Datasheet - Page 4

• Manufacturer Part Number: ICD2051
• Description: Dual Programmable Clock Generator
• Manufacturer: Cypress Semiconductor Corp.

ICD2051:1/95
Revision: April 11, 1995
Derive the proper programming word for a 39.5 MHz output
frequency, using 14.31818 MHz as the reference frequency:
Set I to 0111. The result:
Several choices of P and Q are available:
Table 5. P and Q Value Candidates
Choose (P, Q)=(80,29) for best accuracy (40 ppm).
Therefore:
The programming word, W is generated by concatenating
I=0111, P’=1001101, R=1, M=001, Q’=0011011 to obtain
A LOW-to-HIGH transition on SCLKA/SCLKB (depending on
appropriate channel) is used to shift the programming word W
into DATA as a serial bit stream, LSB first. (See the set-up and
hold timing specifications later in this datasheet.) If more than
22 shifts are performed, only the last 22 data bits received will
be retained.
Glitch-Free Frequency-Modification Procedure
When changing to a new frequency, there is a period of time
when the output signal will be in transition and may glitch due
to changes in the post divider. For applications where it is crit-
ical that the output clock not glitch and always maintain some
known value, the MUXREFA and MUXREFB inputs must be
used. Under normal operation, MUXREF(X) is HIGH and the output
clocks are at the programmed value. When MUXREF(X) is brought
LOW, the reference clock is now multiplexed to the associated out-
put clock. The output remains at this fixed frequency while the pro-
grammed frequency seeks its new value.
When programming the ICD2051, use the MUXREF inputs in
the following manner:
Since 39.5 MHz<40 MHz, double it to 79.0 MHz. Set M to 001.
1. Set MUXREF(X) to a LOW state. This will set the output to the
2. Shift in the desired output frequency value via a 22-bit word
3. After the last bit is shifted in, the VCO will settle to the new
4. Set MUXREF(X) to a HIGH state. This will set the output to the
P
69
80
91
f
P’=P 3=80 3=77=1001101 (4dH)
Q’=Q 2=29 2=27=0011011 (1bH)
W=0111100110110010011011 (1e6c9bH)
reference frequency. The transition is guaranteed to be
glitch-free. (See the timing specifications.)
(as defined above) using the appropriate SCLK and DATA
lines.
state (within .01% of the actual output frequency) within 10
msec.
new programmed frequency. This transition is guaranteed to be
(VCO)
P/Q=2.7857
=79.0=(2 x 14.31818 x P/Q)
Q
25
29
33
f
79.0363
78.9969
78.9669
(VCO)
(MHz)
Error (PPM)
460
40
419
4
Skew-Controlled 2 on CLKA
The CLKA output is available concurrently as 1, 2, and 4
values of the desired output. The 1 and 2 outputs are also closely
matched in order to minimize the phase differences between the
two outputs. Typical phase coherence is less than 2 ns of skew
between the two outputs, with 1 ns or less available as an order
option.
Output Frequency Accuracy
The accuracy of the ICD2051 output frequencies depends on
the target output frequency. As stated previously, the output
frequencies of the ICD2051 are integrally related to the input
reference frequency:
Only certain output frequencies are possible for a particular
reference frequency. However, the ICD2051 normally produc-
es an output frequency within 0.1% of the desired output fre-
quency. Specifics regarding accuracy (ppm) are given for any
desired output frequency as part of the BitCalc program output.
Three-State Output Operation
The OEA or OEB signal, when pulled LOW, will three-state the
clock output line (CLKA or CLKB respectively). This supports
wired-OR connections between external clock lines, and al-
lows for procedures such as automated testing where the
clock must be disabled. The OE signals contain internal
pull-ups; they can be left unconnected if three-state operation
is not required.
Estimating Total Current Drain
Actual current drain is a function of frequency and of circuit
loading. The operating current of a given output is given by the
equation: I=C•V•f, where I=current, C=load capacitance (max. 25
pF), V=output voltage (usually 5V), and f=output frequency (in
MHz).
To calculate total operating current, sum the following:
This gives an approximation of the actual operating current.
For unconnected output pins, one can assume 5 10 pF load-
ing, depending on package type.
Typical values:
Table 6. Typical Load Current Values
glitch-free. (See Serial Programming Timing in the Switching
Waveforms section of this datasheet.)
f
XBUF
CLKA
CLKA/2
CLKA/4
CLKB
Internal
(OUT)
Frequency
=2 x f
high
high
low
(REF)
x P/Q
Load
none
none
high
C•V•f
C•V•f
C•V•f
C•V•f
C•V•f
12 mA
(REF)
(CLKA)
(CLKA/2)
(CLKA/4)
(CLKB)
Current (mA)
ICD2051
100
15
40