AD9540_15 Datasheet, PDF (31/32 Pages) Analog Devices – 655 MHz Low Jitter Clock Generator

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.
AD9540
CFR2[3] Charge Pump Quick Power-Down
Rather than power down the charge pump, which have a long
recovery time, a quick power-down mode that powers down
only the charge pump output buffer is included. Though 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).
Rev. A | Page 31 of 32