EVAL-AD7934-6CB AD [Analog Devices], EVAL-AD7934-6CB Datasheet - Page 24

• Manufacturer Part Number: EVAL-AD7934-6CB
• Description: 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer
• Manufacturer: AD [Analog Devices]

AD7934-6
POWER MODES OF OPERATION
The AD7934-6 has four different power modes of operation.
These modes are designed to provide flexible power manage-
ment options. Different options can be chosen to optimize
the power dissipation/throughput rate ratio for differing
applications. The mode of operation is selected by the power
management bits, PM1 and PM0, in the control register (see
Table 8). When power is first applied to the AD7934-6, an on-
chip, power-on reset circuit ensures that the default power-up
condition is normal mode.
Note that, after power-on, the track-and-hold is in hold mode,
and the first rising edge of CONVST places the track-and-hold
into track mode.
Normal Mode (PM1 = PM0 = 0)
This mode is intended for the fastest throughput rate perform-
ance because the user does not have to allow for power-up times
associated with the AD7934-6. It remains fully powered up at all
times. At power-on reset, this mode is the default setting in the
control register.
Autoshutdown Mode (PM1 = 0; PM0 = 1)
In this mode of operation, the AD7934-6 automatically enters
full shutdown at the end of each conversion, shown at Point A
in Figure 34 and Figure 38. In shutdown mode, all internal
circuitry on the device is powered down. The part retains
information in the control register during shutdown. The track-
and-hold also goes into hold at this point, and remains in hold
as long as the device is in shutdown. The AD7934-6 remains in
shutdown mode until the next rising edge of CONVST (see
Point B in Figure 34 and Figure 38). To keep the device in
shutdown for as long as possible, CONVST should idle low
between conversions as shown in Figure 38. On this rising edge,
the part begins to power-up and the track-and-hold returns to
track mode. The power-up time required is 10 ms minimum
regardless of whether the user is operating with the internal or
external reference. The user should ensure that the power-up
time has elapsed before initiating a conversion.
CONVST
CLKIN
BUSY
1
A
Figure 38. Autoshutdown/Autostandby Modes
14
Rev. A | Page 24 of 28
Autostandby Mode (PM1 = 1; PM0 = 0)
In this mode, the AD7934-6 automatically enters standby mode
at the end of each conversion, shown as Point A in Figure 34.
When this mode is entered, all circuitry on the AD7934-6 is
powered down except for the reference and reference buffer.
The track-and-hold also goes into hold at this point and
remains in hold as long as the device is in standby. The part
remains in standby until the next rising edge of CONVST
powers up the device. The power-up time required depends on
whether the internal or external reference is used. With an
external reference, the power-up time required is a minimum of
600 ns. When using the internal reference, the power-up time
required is a minimum of 7 µs. The user should ensure this
power-up time has elapsed before initiating another conversion
as shown in Figure 38. This rising edge of CONVST also places
the track-and-hold back into track mode.
Full Shutdown Mode (PM1 = 1; PM0 = 1)
When this mode is entered, all circuitry on the AD7934-6 is
powered down upon completion of the write operation, that is,
on rising edge of WR . The track-and-hold enters hold mode at
this point. The part retains the information in the control
register while the part is in shutdown. The AD7934-6 remains
in full shutdown mode, and the track-and-hold in hold mode,
until the power management bits (PM1 and PM0) in the control
register are changed. If a write to the control register occurs
while the part is in full shutdown mode, and the power
management bits are changed to PM0 = PM1 = 0 (normal
mode), the part begins to power up on the WR rising edge, and
the track-and-hold returns to track. To ensure the part is fully
powered up before a conversion is initiated, the power-up time
of 10 ms minimum should be allowed before the CONVST
falling edge; otherwise, invalid data is read.
Note that all power-up times quoted apply with a 470 nF
capacitor on the V
B
t
POWER-UP
REFIN
1
pin.
14