AD7641 Analog Devices, AD7641 Datasheet - Page 16

• Manufacturer Part Number: AD7641
• Description: 18-Bit, 2 MSPS SAR ADC
• Manufacturer: Analog Devices

Specifications of AD7641

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 2MSPS
• Interface: Byte,Par,Ser,SPI
• Analog Input Type: Diff-Bip
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7641
TRANSFER FUNCTIONS
Using the OB/ 2C digital input, except in 18-bit interface mode,
the AD7641 offers two output codings: straight binary and twos
complement. The LSB size with V
262,144, which is 15.623 μV. Refer to Figure 22 and Table 8 for
the ideal transfer characteristic.
1. SEE ANALOG INPUTS SECTION.
2. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
3. THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE. SEE VOLTAGE REFERENCE INPUT SECTION.
4. A 10µF CERAMIC CAPACITOR (X5R, 1206 SIZE) IS RECOMMENDED (FOR EXAMPLE, PANASONIC ECJ3YB0J106M).
5. OPTION, SEE POWER SUPPLY SECTION.
6. OPTION, SEE POWER-UP SECTION.
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
ANALOG
ANALOG
SUPPLY (2.5V)
INPUT +
INPUT –
SEE VOLTAGE REFERENCE INPUT SECTION.
ANALOG
000...010
000...001
000...000
111...110
111...101
111...111
–FSR + 0.5 LSB
–FSR
Figure 22. ADC Ideal Transfer Function
NOTE 2
C
NOTE 2
C
U1
U2
C
C
–FSR + 1 LSB
C
10µF
10µF
REF
NOTE 1
2.7nF
2.7nF
15Ω
NOTE 1
15Ω
100nF
100nF
NOTE 4
ANALOG INPUT
REF
= 2.048 V is 2 × V
REF
REFBUFIN
REFGND
IN+
IN–
AVDD
+FSR – 1.5 LSB
NOTE 3
NOTE 5
AGND
10Ω
+FSR – 1 LSB
10µF
Figure 23. Typical Connection Diagram
DGND
REF
PD
100nF
/
AD7641
Rev. 0 | Page 16 of 28
PDREF
SUPPLY (2.5V)
NOTE 3
DIGITAL
PDBUF
DVDD
Table 8. Output Codes and Ideal Input Voltages
Description
FSR −1 LSB
FSR − 2 LSB
Midscale + 1 LSB
Midscale
Midscale − 1 LSB
−FSR + 1 LSB
−FSR
1
2
This is also the code for overrange analog input (V
+V
This is also the code for underrange analog input (V
−V
OVDD
REF
REF
− V
+ V
100nF
D0/OB/2C
NORMAL
REFGND
REFGND
MODE0
MODE1
SDOUT
CNVST
OGND
RESET
WARP
BUSY
SCLK
CS
RD
).
).
10µF
Analog Input
V
+2.0479844 V
+2.0479688 V
+15.625 μV
0 V
−15.625 μV
−2.0479844 V
−2.048 V
REF
= 2.048 V
10kΩ
NOTE 6
50pF
50pF
50Ω
SERIAL
PORT
OVDD
(2.5V OR 3.3V)
NOTE 7
INTERFACE
DIGITAL
SUPPLY
D
CLOCK
Digital Output Code (Hex)
Straight
Binary
0x3FFFF
0x3FFFE
0x20001
0x20000
0x1FFFF
0x30001
0x30000
IN+
IN+
MICROPROCESSOR/
MICROCONVERTER/
− V
1
2
− V
IN−
IN−
above
Twos
Complement
0x1FFFF
0x1FFFE
0x00001
0x00000
0x3FFFF
0x20001
0x20000
DSP
below
1
2