AD7495BRZ Analog Devices Inc, AD7495BRZ Datasheet - Page 15

• Manufacturer Part Number: AD7495BRZ
• Description: ADC Single SAR 1MSPS 12-Bit Serial 8-Pin SOIC N
• Manufacturer: Analog Devices Inc

Specifications of AD7495BRZ

• Package: 8SOIC N
• Resolution: 12 Bit
• Sampling Rate: 1000 KSPS
• Architecture: SAR
• Number Of Analog Inputs: 1
• Digital Interface Type: Serial (SPI, QSPI, Microwire)
• Input Type: Voltage
• Signal To Noise Ratio: 68 dB
• Polarity Of Input Voltage: Unipolar
• Number Of Bits: 12
• Sampling Rate (per Second): 1M
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 10.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum
source impedance depends on the amount of total harmonic
distortion (THD) that can be tolerated. The THD increases as
the source impedance increases and performance degrades.
Figure 16 shows a graph of the total harmonic distortion vs.
source impedance for various analog input frequencies.
Figure 17 shows a graph of total harmonic distortion vs. analog
input frequency for various supply voltages while sampling at
1 MSPS with an SCLK of 20 MHz.
Digital Inputs
The digital inputs applied to the AD7475/AD7495 are not
limited by the maximum ratings, which limit the analog inputs.
Instead, the digital inputs applied can go to 7 V and are not
restricted by the V
Another advantage of SCLK and CS not being restricted by the
V
avoided. If CS or SCLK are applied before V
of latch-up as there would be on the analog inputs if a signal
greater than 0.3 V were applied prior to V
Figure 16. THD vs. Source Impedance for Various Analog Input Frequencies
DD
Figure 17. THD vs. Analog Input Frequency for Various Supply Voltages
+ 0.3 V limit is that power supply sequencing issues are
–10
–20
–30
–40
–50
–60
–70
–80
–90
–75
–77
–79
–81
–83
–85
–87
–89
–91
–93
–95
1
10
V
DD
= V
V
DD
DD
DRIVE
10
= V
SOURCE IMPEDANCE ( Ω )
+ 0.3 V limit as on the analog inputs.
INPUT FREQUENCY (kHz)
DRIVE
= 5.25V
f
IN
= 4.75V
= 200kHz
f
IN
100
100
= 500kHz
V
DD
V
= V
DD
f
DD
IN
DRIVE
1000
= V
= 10kHz
DD
.
DRIVE
, there is no risk
f
= 2.70V
IN
= 100kHz
= 3.60V
1000
10000
Rev. B | Page 15 of 24
V
The AD7475/AD7495 also has the V
controls the voltage at which the serial interface operates. V
allows the ADC to easily interface to both 3 V and 5 V
processors.
For example, if the AD7475/AD7495 were operated with a V
of 5 V, the V
AD7475/AD7495 have better dynamic performance with a V
of 5 V, while still being able to interface to 3 V digital parts.
Care should be taken to ensure V
more than 0.3 V. (See the Absolute Maximum Ratings section.)
Reference Section
An external reference source should be used to supply the 2.5 V
reference to the AD7475. Errors in the reference source result
in gain errors in the AD7475 transfer function and add the
specified full-scale errors on the part. The AD7475 voltage
reference input, REF IN, has a dynamic input impedance. A
small dynamic current is required to charge the capacitors in
the capacitive DAC during the bit trials. This current is typically
50 μA for a 2.5 V reference. A capacitor of at least 0.1 μF should
be placed on the REF IN pin. Suitable reference sources for the
AD7475 are the AD780, AD680, AD1582, ADR391, ADR381,
ADR431, and ADR03.
The AD7495 contains an on-chip 2.5 V reference. As shown in
Figure 18, the voltage that appears at the REF OUT pin is
internally buffered before being applied to the ADC; the output
impedance of this buffer is typically 10 Ω. The reference is
capable of sourcing up to 2 mA. The REF OUT pin should be
decoupled to AGND using a 100 nF or greater capacitor.
If the 2.5 V internal reference is used to drive another device
that is capable of glitching the reference at critical times, then
the reference has to be buffered before driving the device. To
ensure optimum performance of the AD7495, it is recom-
mended that the internal reference not be over driven. If an
ADC with external reference capability is required, the AD7475
should be used.
DRIVE
DRIVE
160kΩ
V
pin could be powered from a 3 V supply. The
Figure 18. AD7495 Reference Circuit
40kΩ
25Ω
DRIVE
DRIVE
does not exceed V
AD7475/AD7495
REF OUT
feature. This feature
DD
by
DRIVE
DD
DD