AD7453 Analog Devices, AD7453 Datasheet - Page 16

• Manufacturer Part Number: AD7453
• Description: Pseudo Differential, 555 kSPS, 12-Bit A/D Converter in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7453

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 555kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: SOT

AD7453
POWER-UP TIME
The power-up time of the AD7453 is typically 1 µs, which
means that with any frequency of SCLK up to 10 MHz, one
dummy cycle is always sufficient to allow the device to power
up. Once the dummy cycle is complete, the ADC is fully
powered up and the input signal is acquired properly. The quiet
time, t
bus goes back into three-state after the dummy conversion to
the next falling edge of CS .
When running at the maximum throughput rate of 555 kSPS,
the AD7453 powers up and acquires a signal within ±0.5 LSB in
one dummy cycle. When powering up from power-down mode
with a dummy cycle, as in Figure 26, the track and-hold, which
was in hold mode while the part was powered down, returns to
track mode after the first SCLK edge the part receives after the
falling edge of CS . This is shown as Point A in Figure 26.
Although at any SCLK frequency one dummy cycle is sufficient
to power up the device and acquire V
mean that a full dummy cycle of 16 SCLKs must always elapse
to power up the device and acquire V
power up the device and acquire the input signal.
For example, if a 5 MHz SCLK frequency is applied to the ADC,
the cycle time is 3.2 µs (i.e., 1/(5 MHz) × 16). In one dummy
cycle, 3.2 µs, the part is powered up and V
However after 1 µs with a 5 MHz SCLK, only five SCLK cycles
have elapsed. At this stage, the ADC is fully powered up and the
signal acquired. So in this case, CS can be brought high after the
10
to initiate the conversion.
th
SCLK falling edge and brought low again after a time, t
QUIET
SDATA
SCLK
, must still be allowed—from the point at which the
CS
A
1
PART BEGINS
TO POWER UP
INVALID DATA
IN
IN
, it does not necessarily
fully; 1 µs is sufficient to
IN
is acquired fully.
t
10
POWER-UP
Figure 26. Exiting Power-Down Mode
QUIET
Rev. B | Page 16 of 20
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When power supplies are first applied to the AD7453, the ADC
may either power up in the power-down mode or normal mode.
Because of this, it is best to allow a dummy cycle to elapse to
ensure that the part is fully powered up before attempting a
valid conversion. Likewise, if the user wants the part to power
up in power-down mode, the dummy cycle may be used to
ensure the device is in power-down mode by executing a cycle
such as that shown in Figure 25. Once supplies are applied to
the AD7453, the power-up time is the same as that when
powering up from power-down mode. It takes approximately
1 µs to power up fully if the part powers up in normal mode. It
is not necessary to wait 1 µs before executing a dummy cycle to
ensure the desired mode of operation. Instead, the dummy cycle
can occur directly after power is supplied to the ADC. If the
first valid conversion is then performed directly after the
dummy conversion, care must be taken to ensure that adequate
acquisition time has been allowed.
As mentioned earlier, when powering up from the power-down
mode, the part returns to track mode upon the first SCLK edge
applied after the falling edge of CS . However, when the ADC
powers up initially after supplies are applied, the track-and-hold
is already in track mode. This means (assuming one has the
facility to monitor the ADC supply current) that if the ADC
powers up in the desired mode of operation and thus a dummy
cycle is not required to change the mode, then a dummy cycle is
not required to place the track-and-hold into track.
1
THIS PART IS FULLY POWERED
UP WITH V
IN
VALID DATA
FULLY ACQUIRED
10
16