AD7475 Analog Devices, AD7475 Datasheet - Page 14

• Manufacturer Part Number: AD7475
• Description: 1 MSPS, 12-Bit A/D Converter in MSOP-8 or SOIC-8
• Manufacturer: Analog Devices

Specifications of AD7475

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 1MSPS
• Interface: Ser
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: SOIC,SOP

AD7475/AD7495
TYPICAL CONNECTION DIAGRAM
Figure 13 and Figure 15 show typical connection diagrams for
the AD7475 and AD7495, respectively. In both setups the GND
pin is connected to the analog ground plane of the system. In
Figure 13, REF IN is connected to a decoupled 2.5 V supply
from a reference source, the AD780, to provide an analog input
range of 0 V to 2.5 V. Although the AD7475 is connected to a
V
processor. The V
same 3 V supply of the microprocessor to allow a 3 V logic
interface (see the Digital Inputs section.) In Figure 15, the REF
OUT pin of the AD7495 is connected to a buffer and then
applied to a level-shifting circuit used on the analog input to
allow a bipolar signal to be applied to the AD7495. A minimum
100 nF capacitance is required on the REF OUT pin to GND.
The conversion result from both ADCs is output in a 16-bit
word with four leading zeros followed by the MSB of the 12-bit
result. For applications where power consumption is of concern,
the power-down modes should be used between conversions or
bursts of several conversions to improve power performance.
See the Operating Modes section for more information.
INPUT
0V TO
0.1 μ F
(MIN)
2.5V
DD
of 5 V, the serial interface is connected to a 3 V micro-
REF IN
V
V
GND
DD
IN
0.1 μ F
Figure 13. AD7475 Typical Connection Diagram
AD7475
AD780
2.5V
10 μ F
DRIVE
pin of the AD7475 is connected to the
0V
V
SDATA
V
SCLK
DRIVE
5V
SUPPLY
CS
V
0.1 μ F
SERIAL
INTERFACE
3R
R
R
10 μ F
R
SUPPLY
Figure 15. AD7495 Typical Connection Diagram
3V
μ C/ μ P
INPUT
0V TO
2.5V
REF OUT
V
V
GND
Rev. B | Page 14 of 24
DD
IN
0.1μF
0.1μF
(MIN)
AD7495
10μF
Analog Input
Figure 14 shows an equivalent circuit of the analog input
structure of the AD7475/AD7495. The D1 and D2 diodes
provide ESD protection for the analog inputs. Care must be
taken to ensure that the analog input signal never exceeds the
supply rails by more than 200 mV. This causes these diodes to
become forward-biased and start conducting current into the
substrate. The maximum current these diodes can conduct
without causing irreversible damage to the part is 20 mA.
The capacitor C1 in Figure 14 is typically about 4 pF and can
primarily be attributed to pin capacitance. The resistor R1 is a
lumped component made up of the on resistance of a switch.
This resistor is typically about 100 Ω. The capacitor C2 is
the ADC sampling capacitor and has a capacitance of 16 pF,
typically. For ac applications, it is recommended to remove
high frequency components from the analog input signal
using an RC low-pass filter on the relevant analog input pin. In
applications where harmonic distortion and signal-to-noise
ratio are critical, the analog input should be driven from a low
impedance source. Large source impedances significantly affect
the ac performance of the ADC. This may necessitate the use of
an input buffer amplifier. The choice of the op amp is a function
of the particular application.
SDATA
V
SCLK
DRIVE
5V
SUPPLY
CS
V
IN
0.1μF
4pF
C1
SERIAL
INTERFACE
Figure 14. Equivalent Analog Input Circuit
V
10μF
DD
D1
D2
CONVERSION PHASE: SWITCH OPEN
TRACK PHASE: SWITCH CLOSED
SUPPLY
3V
R1
μC/μP
16pF
C2