AD9520-0/PCBZ Analog Devices Inc, AD9520-0/PCBZ Datasheet - Page 50

• Manufacturer Part Number: AD9520-0/PCBZ
• Description: 12/24 Channel Clock Gen 2,0GH
• Manufacturer: Analog Devices Inc

Specifications of AD9520-0/PCBZ

• Design Resources: Synchronizing Multiple AD9910 1 GSPS Direct Digital Synthesizers (CN0121) Phase Coherent FSK Modulator (CN0186)
• Main Purpose: Timing, Clock Generator
• Utilized Ic / Part: AD9520-0
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9520-0
Soft Reset via the Serial Port
The serial port control register allows for a soft reset by setting
Bit 2 and Bit 5 in Register 0x000. When Bit 5 and Bit 2 are set,
the chip enters a soft reset mode and restores the chip either to
the setting stored in EEPROM (the EEPROM pin = 1) or to the
on-chip setting (the EEPROM pin = 0), except for Register 0x000.
These bits are self-clearing. During the internal reset, the outputs
are held static.
Soft Reset to Settings in EEPROM when EEPROM Pin = 0 via
the Serial Port
The serial port control register allows the chip to be reset to
settings in EEPROM when the EEPROM pin = 1 via 0xB02[1].
This bit is self-clearing. This bit does not have any effect when
the EEPROM pin = 0. It takes ~20 ms for the outputs to begin
toggling after the Soft_EEPROM register is cleared.
POWER-DOWN MODES
Chip Power-Down via PD
The AD9520 can be put into a power-down condition by
pulling the PD pin low. Power-down turns off most of the
functions and currents inside the AD9520. The chip remains
in this power-down state until PD is brought back to logic high.
When taken out of power-down mode, the AD9520 returns to
the settings programmed into its registers prior to the power-
down, unless the registers are changed by new programming
while the PD pin is held low.
Powering down the chip shuts down the currents on the chip,
except for the bias current necessary to maintain the LVPECL
outputs in a safe shutdown mode. The LVPECL bias currents are
needed to protect the LVPECL output circuitry from damage that
can be caused by certain termination and load configurations
when tristated. Because this is not a complete power-down, it
can be called sleep mode. The AD9520 contains special circuitry to
prevent runt pulses on the outputs when the chip is entering or
exiting sleep mode.
When the AD9520 is in a PD power-down, the chip is in the
following state:
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The PLL is off (asynchronous power-down).
The VCO is off.
The CLK input buffer is off, but the CLK input dc bias
circuit is on.
In differential mode, the reference input buffer is off, and
the dc bias circuit is still on.
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PLL Power-Down
The PLL section of the AD9520 can be selectively powered
down. There are two PLL power-down modes set by
Register 0x010[1:0]: asynchronous and synchronous.
In asynchronous power-down mode, the device powers down as
soon as the registers are updated. In synchronous power-down
mode, the PLL power-down is gated by the charge pump to
prevent unwanted frequency jumps. The device goes into power-
down on the occurrence of the next charge pump event after the
registers are updated.
Distribution Power-Down
The distribution section can be powered down by writing
0x230[1] = 1b, which turns off the bias to the distribution
section. If the LVPECL power-down mode is normal operation
(0b), it is possible for a low impedance load on that LVPECL
output to draw significant current during this power-down. If
the LVPECL power-down mode is set to 1b, the LVPECL output
is not protected from reverse bias and can be damaged under
certain termination conditions.
Individual Clock Output Power-Down
Any of the clock distribution outputs can be powered down
into safe power-down mode by individually writing to the
appropriate registers. The register map details the individual
power-down settings for each output. These settings are found
in Register 0x0F0[0] to Register 0x0FD[0].
Individual Clock Channel Power-Down
Any of the clock distribution channels can be powered down
individually by writing to the appropriate registers. Powering
down a clock channel is similar to powering down an individual
driver, but it saves more power because the dividers are also
powered down. Powering down a clock channel also automatically
powers down the drivers connected to it. The register map
details the individual power-down settings for each output
channel. These settings are found in 0x192[2], 0x195[2],
0x198[2], and 0x19B[2].
In singled-ended mode, the reference input buffer is off,
but the dc bias circuit is off.
All dividers are off.
All CMOS outputs are tristated.
All LVPECL outputs are in safe off mode.
The serial control port is active, and the chip responds to
commands.