AD7829 AD [Analog Devices], AD7829 Datasheet - Page 12

• Manufacturer Part Number: AD7829
• Description: 3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel Sampling ADCs
• Manufacturer: AD [Analog Devices]

AD7822/AD7825/AD7829
OPERATING MODES
The AD7822, AD7825, and AD7829 have two possible modes
of operation, depending on the state of the CONVST pulse
approximately 100 ns after the end of a conversion, i.e., upon
the rising edge of the EOC pulse.
Mode 1 Operation (High-Speed Sampling)
When the AD7822, AD7825, and AD7829 are operated in
Mode 1 they are not powered-down between conversions. This
mode of operation allows high throughput rates to be achieved.
Figure 20 shows how this optimum throughput rate is achieved
by bringing CONVST high before the end of a conversion, i.e.,
before the EOC pulses low. When operating in this mode, a new
conversion should not be initiated until 30 ns after the end of a
read operation. This is to allow the track/hold to acquire the
analog signal to 0.5 LSB accuracy.
DB0–DB7
CONVST
EOC
DB0–DB7
RD
CS
CONVST
EOC
CS
RD
TRACK
t
t
POWER-UP
2
120ns
HOLD
t
1
Figure 20. Mode 1 Operation
Figure 21. Mode 2 Operation
t
1
–12–
Mode 2 Operation (Automatic Power-Down)
When the AD7822, AD7825, and AD7829 are operated in
Mode 2 (see Figure 21), they automatically power down at the
end of a conversion. The CONVST signal is brought low to ini-
tiate a conversion and is left logic low until after the EOC goes
high, i.e., approximately 100 ns after the end of the conversion.
The state of the CONVST signal is sampled at this point (i.e.,
530 ns maximum after CONVST falling edge) and the AD7822,
AD7825, and AD7829 will power down as long as CONVST
is low. The ADC is powered up again on the rising edge of the
CONVST signal. Superior power performance can be achieved
in this mode of operation by only powering up the AD7822,
AD7825, and AD7829 to carry out a conversion. The parallel
interface of the AD7822, AD7825, and AD7829 is still fully
operational while the ADCs are powered down. A read may occur
while the part is powered down, and so it does not necessarily
need to be placed within the EOC pulse as shown in Figure 21.
TRACK
VALID
DATA
VALID
DATA
POWER
DOWN
HERE
t
3
HOLD
REV. B