AD7477ARTZ-REEL7 Analog Devices Inc, AD7477ARTZ-REEL7 Datasheet - Page 16

• Manufacturer Part Number: AD7477ARTZ-REEL7
• Description: IC,A/D CONVERTER,SINGLE,10-BIT,CMOS,TSOP,6PIN
• Manufacturer: Analog Devices Inc

Specifications of AD7477ARTZ-REEL7

• Number Of Bits: 10
• Sampling Rate (per Second): 1M
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 17.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7477CBZ - BOARD EVALUATION FOR AD7477
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table II provides some typical performance data with various
op amps used as the input buffer for a 100 kHz input tone at
room temperature under the same setup conditions.
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum
source impedance will depend on the amount of total harmonic
distortion (THD) that can be tolerated. The THD will increase
as the source impedance increases and the performance will
degrade. See TPC 7.
Digital Inputs
The digital inputs applied to the AD7476A/AD7477A/AD7478A
are not limited by the maximum ratings that limit the analog
input. Instead, the digital inputs applied can go to 7 V and are
not restricted by the V
For example, if the AD7476A/AD7477A/AD7478A were oper-
ated with a V
the digital inputs. However, it is important to note that the data
output on SDATA will still have 3 V logic levels when V
Another advantage of SCLK and CS not being restricted by the
V
issues are avoided. If CS or SCLK is applied before V
is no risk of latch-up as there would be on the analog input if a
signal greater than 0.3 V was applied prior to V
MODES OF OPERATION
The mode of operation of the AD7476A/AD7477A/AD7478A is
selected by controlling the (logic) state of the CS signal during a
conversion. There are two possible modes of operation: normal
and power-down. The point at which CS is pulled high after the
conversion has been initiated will determine whether the
AD7476A/AD7477A/AD7478A will enter power-down mode or
not. Similarly, if already in power-down, CS can control
whether the device will return to normal operation or remain in
power-down. These modes of operation are designed to provide
flexible power management options. These options can be
chosen to optimize the power dissipation/throughput rate ratio for
different application requirements.
Normal Mode
This mode is intended for the fastest throughput rate perfor-
mance; the user does not have to worry about any power-up
times with the AD7476A/AD7477A/AD7478A remaining fully
powered all the time. Figure 9 shows the general diagram of the
operation of the AD7476A/AD7477A/AD7478A in this mode.
The conversion is initiated on the falling edge of CS as described
in the Serial Interface section. To ensure that the part remains
fully powered up at all times, CS must remain low until at least
10 SCLK falling edges have elapsed after the falling edge of CS.
If CS is brought high any time after the 10th SCLK falling edge
but before the end of the t
ered up, but the conversion will be terminated and SDATA will
go back into three-state.
AD7476A/AD7477A/AD7478A
DD
Table II. AD7476A Typical Performance with Various
Input Buffers, V
Op Amp in the
Input Buffer
AD711
AD797
AD845
+ 0.3 V limit is the fact that power supply sequencing
DD
of 3 V, then 5 V logic levels could be used on
DD
DD
= 3 V
+ 0.3 V limit as on the analog input.
CONVERT
AD7476A SNR Performance
(dB)
72.3
72.5
71.4
, the part will remain pow-
DD
.
DD
DD
, there
= 3 V.
–16–
For the AD7476A, 16 serial clock cycles are required to com-
plete the conversion and access the complete conversion results.
For the AD7477A and AD7478A, a minimum of 14 and 12
serial clock cycles are required to complete the conversion and
access the complete conversion results, respectively.
CS may idle high until the next conversion or may idle low until
CS returns high sometime prior to the next conversion (effec-
tively idling CS low).
Once a data transfer is complete (SDATA has returned to
three-state), another conversion can be initiated after the quiet
time, t
Power-Down Mode
This mode is intended for use in applications where slower
throughput rates are required; either the ADC is powered down
between each conversion, or a series of conversions is performed
at a high throughput rate and the ADC is then powered down
for a relatively long duration between these bursts of several
conversions. When the AD7476A/AD7477A/AD7478A is in
power-down, all analog circuitry is powered down.
To enter power-down, the conversion process must be inter-
rupted by bringing CS high anywhere after the second falling
edge of SCLK and before the 10th falling edge of SCLK, as
shown in Figure 10. Once CS has been brought high in this
window of SCLKs, the part will enter power-down, the con-
version that was initiated by the falling edge of CS will be
terminated, and SDATA will go back into three-state. If CS is
brought high before the second SCLK falling edge, the part will
remain in normal mode and will not power down. This will
avoid accidental power-down due to glitches on the CS line.
In order to exit this mode of operation and power up the
AD7476A/AD7477A/AD7478A again, a dummy conversion is
performed. On the falling edge of CS, the device will begin to
power up and will continue to power up as long as CS is held low
until after the falling edge of the 10th SCLK. The device will be
fully powered up once 16 SCLKs have elapsed, and valid data
will result from the next conversion as shown in Figure 11. If CS
is brought high before the 10th falling edge of SCLK, then the
AD7476A/AD7477A/AD7478A will go back into power-down.
This avoids accidental power-up due to glitches on the CS line or
an inadvertent burst of eight SCLK cycles while CS is low. So
although the device may begin to power up on the falling edge of
CS, it will power down again on the rising edge of CS as long as it
occurs before the 10th SCLK falling edge.
Power-Up Time
The power-up time of the AD7476A/AD7477A/AD7478A is
1 µs, which means that with any frequency of SCLK up to 20 MHz,
one dummy cycle will always be sufficient to allow the device to
power up. Once the dummy cycle is complete, the ADC will be
fully powered up and the input signal will be acquired properly.
The quiet time, t
where the bus goes back into three-state after the dummy con-
version to the next falling edge of CS. When running at a 1 MSPS
throughput rate, the AD7476A/AD7477A/AD7478A will power
up and acquire a signal within ± 0.5 LSB in one dummy
cycle, i.e., 1 µs.
When powering up from the power-down mode with a dummy
cycle, as in Figure 11, the track-and-hold that 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 11. Although at any
QUIET
, has elapsed by bringing CS low again.
QUIET
, must still be allowed from the point
REV. C