Datasheet

AD9920A
Rev. B | Page 86 of 112
STANDBY MODE OPERATION
The AD9920A contains three standby modes to optimize the
overall power dissipation in a particular application. Bits[1:0]
of Address 0x00 control the power-down state of the device.
Table 48. Power States Set by Standby Register
Standby Register,
Bits[1:0] Description
00 Normal operation (full power)
01 Standby1 mode
10 Standby2 mode
11 Standby3 mode (lowest power)
Tabl e 4 9 and Table 50 summarize the operation of each power-
down mode. The OUT_CONTROL register takes priority over
the Standby1 and Standby2 modes in determining the digital
output states, but Standby3 mode takes priority over OUT_
CONTROL. Standby3 has the lowest power consumption and
even shuts down the crystal oscillator circuit between CLI and
CLO. Therefore, if CLI and CLO are being used with a crystal
to generate the master clock, this circuit is powered down, and
there is no clock signal.
When returning from Standby3 mode to normal operation, the
timing core must be reset at least 500 μs after the STANDBY
register is written to. This allows sufficient time for the crystal
circuit to settle.
The vertical outputs can also be programmed to hold a specific
value during the Standby3 mode by using Address 0x26. This
register is useful during power-up if different polarities are
required by the V-driver and CCD to prevent damage when VH
and VL areas are applied. The polarities for Standby1 mode and
Standby2 mode are also programmable, using Address 0x25, and
OUT_CONTROL = low uses the same polarities programmed
for Standby1 and Standby2 modes in Address 0x25. The GPO
polarities are programmable using Address 0x27.
Note that the GPO outputs are high-Z by default at power-up
until Address 0x7A is used to select them as outputs.
CLI FREQUENCY CHANGE
If the input clock CLI is interrupted or changed to a different
frequency, the timing core must be reset for proper operation.
After the CLI clock has settled to the new frequency, or the
previous frequency is resumed, write 0 and then 1 to the
TGCORE_
RST
register (Address 0x14). This guarantees
that the timing core operates properly.
Table 49. Standby Mode Operation for HCLKMODE = 0x1, 0x2, or 0x4
(Standby Polarities for XV, XSUBCK, and GPO Outputs Are Programmable)
I/O Block Standby3 (Default)
1, 2
OUT_CONTROL = Low
2
Standby2
3, 4
Standby1
3, 4
AFE Off No change Off Only REFT, REFB on
Timing Core Off No change Off On
CLO Oscillator Off No change Off On
CLO Low No change Low Running
H1 High-Z Low Low (4.3 mA) Low (4.3 mA)
H2 High-Z High High (4.3 mA) High (4.3 mA)
H3 High-Z Low Low (4.3 mA) Low (4.3 mA)
H4 High-Z High High (4.3 mA) High (4.3 mA)
H5 High-Z Low Low (4.3 mA) Low (4.3 mA)
H6 High-Z High High (4.3 mA) High (4.3 mA)
H7 High-Z Low Low (4.3 mA) Low (4.3 mA)
H8 High-Z High High (4.3 mA) High (4.3 mA)
HL High-Z Low Low (4.3 mA) Low (4.3 mA)
RG High-Z Low Low (4.3 mA) Low (4.3 mA)
VD Low
VDHDPOL
value VDHDPOL value
Running
HD Low
VDHDPOL
value VDHDPOL value
Running
DCLK Low Running Low Running
D0 to D11 Low Low Low Low
XV1 to XV24 Low Low Low Low
XSUBCK Low Low Low Low
GPO1 to GPO4,
GPO7, and GPO8
Low Low Low Low
1
To exit Standby3 or Standby2 mode, write 00 to the standby register (Address 0x00, Bits[1:0]) and then reset the timing core after 500 μs to guarantee proper settling of the
oscillator and external crystal.
2
Standby3 mode takes priority over OUT_CONTROL for determining the output polarities.
3
These polarities assume OUT_CONTROL = high because OUT_CONTROL = low takes priority over Standby1 and Standby2.
4
Standby1 and Standby2 set H and RG drive strength to minimum value (4.3 mA).