AD9510-VCOSLASHPCB datasheet(33/60 Pages) AD

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AD9510

Rev. A | Page 33 of 60

FUNCTION PIN

The FUNCTION pin (16) has three functions that are selected

by the value in Register 58h<6:5>. This pin is internally pulled

down by a 30 kΩ resistor. If this pin is left NC, the part is in

reset by default. To avoid this, connect this pin to VS with a

1 kΩ resistor.

RESETB: 58h<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 synchronous sync is issued (see the SYNCB: 58h<6:5>

= 01b section) and the AD9510 resumes operation according to

the default values of the registers.

SYNCB: 58h<6:5> = 01b

The FUNCTION pin may be used to cause 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 each divider’s start high bit. 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 divider’s phase offset bits.

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: 58h<6:5> = 11b

The FUNCTION pin may 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.

See the Chip Power-Down or Sleep Mode—PDB section for

more details on what occurs during a PDB initiated power-

down.

DISTRIBUTION SECTION

As previously mentioned, the AD9510 is partitioned into two

operational sections: PLL and distribution. The PLL Section

was discussed previously. If desired, the distribution section can

be used separately from the PLL section.

CLK1 AND CLK2 CLOCK INPUTS

Either CLK1 or CLK2 may be selected as the input to the

distribution 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 45h<0> = 1. This is

the power-up default state.

CLK1 and CLK2 work for inputs up to 1600 MHz. The jitter

performance is improved by a higher input slew rate. The input

level should 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 could degrade the

jitter performance.

See Figure 35 for the CLK1 and CLK2 equivalent input circuit.

These inputs are fully differential and self-biased. The signal

should 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. The other side of the input

should be bypassed to a quiet ac ground by a capacitor.

The unselected clock input (CLK1 or CLK2) should be powered

down 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 the AD9510 has its own

divider. The divider can be bypassed to get 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 may 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.

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