Datasheet
AD7623
Rev. 0 | Page 16 of 28
TRANSFER FUNCTIONS
Using the OB/
2C
digital input, the AD7623 offers two output
codings: straight binary and twos complement. The LSB size
with V
REF
= 2.048 V is 2 × V
REF
/65536, which is 62.5 μV. Refer to
Figure 22 and Table 7 for the ideal transfer characteristic.
05574-022
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE (Straight Binary)
ANALOG INPUT
+FSR–1.5 LSB
+FSR–1 LSB–FSR+1 LSB
–FSR
–FSR+0.5 LSB
Figure 22. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Digital Output Code
Description
Analog Input
V
REF
= 2.048 V
Straight
Binary
Twos
Complement
FSR −1 LSB +2.047938 V 0xFFFF
1
0x7FFF
1
FSR − 2 LSB +2.047875 V 0xFFFE 0x7FFE
Midscale + 1 LSB +62.5 μV 0x8001 0x0001
Midscale 0 V 0x8000 0x0000
Midscale − 1 LSB −62.5 μV 0x7FFF 0xFFFF
−FSR + 1 LSB −2.047938 V 0x0001 0x8001
−FSR −2.048 V 0x0000
2
0x8000
2
1
This is also the code for overrange analog input (V
IN+
− V
IN−
above
V
REF
− V
REFGND
).
2
This is also the code for underrange analog input (V
IN+
− V
IN−
below
−V
REF
+ V
REFGND
).
05574-023
RD
CS
100nF 100nF
AVDD
10μF
100nF
AGND DGND DVDD OVDD OGND
CNVST
BUSY
SDOUT
SCLK
RESET
PD
REFBUFIN
10Ω
D
CLOCK
AD7623
MICROCONVERTER/
MICROPROCESSOR/
DSP
SERIAL
PORT
DIGITAL
INTERFACE
SUPPLY
(2.5V OR 3.3V)
ANALOG
SUPPLY (2.5V)
OVDD
DIGITAL
SUPPLY (2.5V)
IN+
IN–
U2
10Ω
NOTE 5
50Ω
50pF
NOTE 1
ANALOG
INPUT +
C
C
C
C
1nF
1nF
U1
10Ω
NOTE 1
SER/PAR
OB/2C
REFGND
REF
PDBUF
PDREF
100nF
ANALOG
INPUT –
NOTE 2
NOTE 2
NOTE 3
NOTE 4
NOTE 3
NOTE 7
NOTE 6
10μF
10μF
C
REF
10μF
10kΩ
50pF
1. SEE ANALOG INPUT 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).
SEE VOLTAGE REFERENCE INPUT SECTION.
5. OPTION, SEE POWER SUPPLY SECTION.
6. OPTION, SEE POWER-UP SECTION.
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
Figure 23. Typical Connection Diagram