AD9540PCB datasheet(31/32 Pages) AD

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AD9540

Rev. 0 | Page 31 of 32

CFR2<7:6> Open

Unused locations. Write a Logic 0.

CFR2<5> CP Polarity

This bit sets the polarity of the charge pump in response to a

ground referenced or a supply referenced VCO.

CFR2<5> = 0 (default). The charge pump is configured to

operate with a supply referenced VCO. If CLK2 lags REFIN, the

charge pump attempts to drive the VCO control node voltage

higher. If CLK2 leads REFIN, the charge pump attempts to drive

the VCO control node voltage lower.

CFR2<5> = 1. The charge pump is configured to operate with a

ground referenced VCO. If CLK2 lags REFIN, the charge pump

attempts to drive the VCO control node voltage lower. If CLK2

leads REFIN, the charge pump attempts to drive the VCO

control node voltage higher.

CFR2<4> Charge Pump Full Power-Down

This bit, when set, puts the charge pump into a full power-down

mode.

CFR2<4> = 0 (default). The charge pump is powered on and

operating normally.

CFR2<4> = 1. The charge pump is powered down completely.

CFR2<3> Charge Pump Quick Power-Down

Rather than power down the charge pump, which can take a

long time to recover from, a quick power-down mode that pow-

ers down only the charge pump output buffer is included. While

this does not reduce the power consumption significantly, it

does shut off the output to the charge pump and allows it to

come back on rapidly.

CFR2<3> = 0 (default). The charge pump is powered on and

operating normally.

CFR2<3> = 1. The charge pump is on and running, but the

output buffer is powered down.

CFR2<2:0> Charge Pump Current Scale

A base output current from the charge pump is determined by a

resistor connected from the CP_RSET pin to ground (see the

PLL Circuitry section). However, it is possible to multiply the

charge pump output current by a value from 1:8 by program-

ming these bits. The charge pump output current is scaled by

CFR2<2:0> +1.

CFR2<2:0> = 000 (default)

Scale factor = 1 to CFR2<2:0> = 111 (8).

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