AD9516-5
Rev. A | Page 43 of 76
RESET MODES
The
AD9516 has several ways to force the chip into a reset
condition that restores all registers to their default values and
makes these settings active.
Power-On Reset—Start-Up Conditions When VS Is Applied
A power-on reset (POR) is issued when the VS power supply is
turned on. The POR pulse duration is <100 ms and initializes
the chip to the power-on conditions that are determined by the
default register settings. These are indicated in the Default Value
a SYNC operation, which brings the outputs into phase alignment
according to the default settings. It is recommended that the
user not toggle SCLK during the reset pulse.
Asynchronous Reset via the RESET Pin
An asynchronous hard reset is executed by momentarily pulling
RESET low. A reset restores the chip registers to the default settings.
It is recommended that the user not toggle SCLK for 20 ns after
RESET goes high.
Soft Reset via Register 0x000[2]
A soft reset is executed by writing Register 0x000[2] and
Register 0x000[5] = 1b. This bit is not self-clearing; therefore,
it must be cleared by writing Register 0x000[2] and Register
0x000[2] = 0b to reset it and complete the soft reset operation.
A soft reset restores the default values to the internal registers.
The soft reset bit does not require an update registers command
(Register 0x232 = 0x01) to be issued.
POWER-DOWN MODES
Chip Power-Down via PD
The
AD9516 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
. The chip remains in this power-down
state until
PD is brought back to logic high. When the
wakes up, it 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.
The PD power-down shuts down the currents on the chip, except
the bias current that is necessary to maintain the LVPECL outputs
in a safe shutdown mode. This is 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.
When the
AD9516 is in a PD power-down, the chip is in the
following state:
The PLL is off (asynchronous power-down).
The CLK input buffer is off.
All dividers are off.
All LVDS/CMOS outputs are off.
All LVPECL outputs are in safe off mode.
The serial port is active and responds to commands.
If the
AD9516 clock outputs must be synchronized to each
other, a SYNC is required upon exiting power-down (see the
PLL Power-Down
The PLL section of the
AD9516 can be selectively powered
down. There are three PLL operating modes that are set by
Register 0x010[1:0], as shown in
Table 49.
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 to
Register 0x230[1] = 1b. This turns off the bias to the distribution
section. If the LVPECL power-down mode is normal operation
(00b), 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 11b, 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
individually by writing to the appropriate registers. The register
map details the individual power-down settings for each output.
The LVDS/CMOS outputs can be powered down, regardless of
their output load configuration.
The LVPECL outputs have multiple power-down modes
(see
Table 53) that give some flexibility in dealing with the
various output termination conditions. When the mode is set to
10b, the LVPECL output is protected from reverse bias to
2 VBE + 1 V. If the mode is set to 11b, the LVPECL output is
not protected from reverse bias and can be damaged under
certain termination conditions. This setting also affects the
operation when the distribution block is powered down with
Individual Circuit Block Power-Down
Other
AD9516 circuit blocks (such as CLK, REF1, and REF2)
can be powered down individually. This gives flexibility in
configuring the part for power savings whenever certain chip
functions are not needed.