ICS84021 Datasheet, PDF (2/14 Pages) Integrated Circuit Systems – 260MHZ, CRYSTAL-TO-LVCMOS / LVTTL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS84021
260MHZ, CRYSTAL-TO-LVCMOS / LVTTL
FREQUENCY SYNTHESIZER
FUNCTIONAL DESCRIPTION
NOTE: The functional description that follows describes op-
eration using a 25MHz crystal. Valid PLL loop divider values
for different crystal or input frequencies are defined in the
Input Frequency Characteristics, Table 5, NOTE 1.
The ICS84021 features a fully integrated PLL and therefore
requires no external components for setting the loop band-
width. A fundamental crystal is used as the input to the on-
chip oscillator. The output of the oscillator is fed into the phase
detector. A 25MHz crystal provides a 25MHz phase detector
reference frequency. The VCO of the PLL operates over a
range of 620MHz to 780MHz. The output of the M divider is
also applied to the phase detector.
The phase detector and the M divider force the VCO output
frequency to be M times the reference frequency by adjusting
the VCO control voltage. Note that for some values of M (either
too high or too low), the PLL will not achieve lock. The output of
the VCO is scaled by a divider prior to being sent to each of
the LVCMOS output buffers. The divider provides a 50% out-
put duty cycle.
The programmable features of the ICS84021 support two input
modes to program the M divider and N output divider. The two
input operational modes are parallel and serial. Figure 1 shows
the timing diagram for each mode. In parallel mode, the
nP_LOAD input is initially LOW. The data on inputs M0 through
M8 and N0 and N1 is passed directly to the M divider and
N output divider. On the LOW-to-HIGH transition of the nP_LOAD
input, the data is latched and the M divider remains loaded until
the next LOW transition on nP_LOAD or until a serial event oc-
curs. As a result, the M and N bits can be hardwired to set the
M divider and N output divider to a specific default state that will
automatically occur during power-up. The TEST output is LOW
when operating in the parallel input mode. The relationship be-
tween the VCO frequency, the crystal frequency and the M di-
vider is defined as follows: fVCO = fxtal x M
The M value and the required values of M0 through M8 are
shown in Table 3B, Programmable VCO Frequency Function
Table. Valid M values for which the PLL will achieve lock for a
25MHz reference are defined as 25 ≤ M ≤ 31. The frequency
out is defined as follows: FOUT = fVCO = fxtal x M
N
N
Serial operation occurs when nP_LOAD is HIGH and
S_LOAD is LOW. The shift register is loaded by sampling
the S_DATA bits with the rising edge of S_CLOCK. The con-
tents of the shift register are loaded into the M divider and N
output divider when S_LOAD transitions from LOW-to-HIGH.
The M divide and N output divide values are latched on the
HIGH-to-LOW transition of S_LOAD. If S_LOAD is held HIGH,
data at the S_DATA input is passed directly to the M divider
and N output divider on each rising edge of S_CLOCK. The
serial mode can be used to program the M and N bits and
test bits T1 and T0. The internal registers T0 and T1 deter-
mine the state of the TEST output as follows:
T1 T0
TEST Output
00
LOW
01
S_DATA, Shift Register Input
10
Output of M divider
11
CMOS Fout
S_CLOCK
SERIAL LOADING
S_DATA
S_LOAD
T 1 T0 *NULL N1 N0 M8 M7 M6 M5 M4 M3 M2 M1 M 0
tt
SH
nP_LOAD
t
S
PARALLEL LOADING
M0:M8, N0:N1
M, N
nP_LOAD
tt
SH
Time
FIGURE 1. PARALLEL & SERIAL LOAD OPERATIONS
*NOTE: The NULL timing slot must be observed.
84021AY
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2
REV. A NOVEMBER 7, 2003