AD9510
Data Sheet
Rev. B | Page 32 of 56
FUNCTION PIN
The FUNCTION pin (16) has three functions that are selected
by the value in Register 0x58[6:5]. This pin is internally pulled
down by a 30 k resistor. If this pin is left unconnected, the
part is in reset by default. To avoid this, connect this pin to VS
with a 1 k resistor.
RESETB: Register 0x58[6:5] = 00b (Default)
In its default mode, the FUNCTION pin acts as RESETB, which
generates an asynchronous reset or hard reset when pulled low.
The resulting reset writes the default values into the serial control
port buffer registers as well as loading them into the chip control
registers. When the RESETB signal goes high again, a synchro-
default values of the registers.
SYNCB: Register 0x58[6:5] = 01b
Using the FUNCTION pin causes a synchronization or
alignment of phase among the various clock outputs. The
synchronization applies only to clock outputs that
Are not powered down
The divider is not masked (no sync = 0b)
Are not bypassed (bypass = 0b)
SYNCB is level and rising edge sensitive. When SYNCB is low,
the set of affected outputs are held in a predetermined state,
defined by the start high bit of each divider. On a rising edge,
the dividers begin after a predefined number of fast clock cycles
(fast clock is the selected clock input, CLK1 or CLK2) as
determined by the values in the phase offset bits of the divider.
The SYNCB application of the FUNCTION pin is always active,
regardless of whether the pin is also assigned to perform reset
or power-down. When the SYNCB function is selected, the
FUNCTION pin does not act as either RESETB or PDB.
PDB: Register 0x58[6:5] = 11b
The FUNCTION pin can also be programmed to work as an
asynchronous full power-down, PDB. Even in this full power-
down mode, there is still some residual VS current because
some on-chip references continue to operate. In PDB mode,
the FUNCTION pin is active low. The chip remains in a power-
down state until PDB is returned to logic high. The chip returns
to the settings programmed prior to the power-down.
details on what occurs during a PDB initiated power-down.
DISTRIBUTION SECTION
As previously mentioned, the
AD9510 is partitioned into two
discussed previously in this data sheet. If desired, the distribution
section can be used separately from the PLL section.
CLK1 AND CLK2 CLOCK INPUTS
Either CLK1 or CLK2 can be selected as the input to the distri-
bution section. The CLK1 input can be connected to drive the
distribution section only. CLK1 is selected as the source for the
distribution section by setting Register 0x45[0] = 1. This is the
power-up default state.
CLK1 and CLK2 work for inputs up to 1600 MHz. A higher input
slew rate improves the jitter performance. The input level must
be between approximately 150 mV p-p to no more than 2 V p-p.
Anything greater may result in turning on the protection diodes
on the input pins, which may degrade the jitter performance.
These inputs are fully differential and self-biased. The signal
must be ac-coupled using capacitors. If a single-ended input
must be used, this can be accommodated by ac-coupling to one
side of the differential input only. Bypass the other side of the
input to a quiet ac ground by a capacitor.
Power down the unselected clock input (CLK1 or CLK2) to
eliminate any possibility of unwanted crosstalk between the
selected clock input and the unselected clock input.
DIVIDERS
Each of the eight clock outputs of th
e AD9510 has its own
divider. The divider can be bypassed to obtain an output at the
same frequency as the input (1×). When a divider is bypassed,
it is powered down to save power.
All integer divide ratios from 1 to 32 can be selected. A divide
ratio of 1 is selected by bypassing the divider.
Each divider can be configured for divide ratio, phase, and duty
cycle. The phase and duty cycle values that can be selected
depend on the divide ratio that is chosen.
Setting the Divide Ratio
The divide ratio is determined by the values written via the serial
control port (SCP) to the registers that control each individual
output, OUT0 to OUT7. These are the even numbered registers
beginning at Register 0x48 and going through Register 0x56.
Each of these registers is divided into bits that control the
number of clock cycles that the divider output stays high
(HIGH_CYCLES[3:0]) and the number of clock cycles that the
divider output stays low (LOW_CYCLES[7:4]). Each value is 4
bits and has the range of 0 to 15.
The divide ratio is set by
Divide Ratio = (HIGH_CYCLES + 1) + (LOW_CYCLES + 1)