Datasheet
AD7634 Data Sheet
Rev. B | Page 18 of 32
Warp Mode
Setting WARP = high and IMPULSE = low allows the fastest
conversion rate of up to 670 kSPS. However, in this mode, the
full-specified accuracy is guaranteed only when the time between
conversions does not exceed 1 ms. If the time between two
consecutive conversions is longer than 1 ms (after power-up),
the first conversion result should be ignored because in warp mode,
the ADC performs a background calibration during the SAR
conversion process. This calibration can drift if the time between
conversions exceeds 1 ms thus causing the first conversion to
appear offset. This mode makes the AD7634 ideal for applications
where both high accuracy and fast sample rate are required.
Normal Mode
Setting WARP = IMPULSE = low or WARP = IMPULSE = high
allows the fastest mode (570 kSPS) without any limitation on
time between conversions. This mode makes the AD7634 ideal
for asynchronous applications such as data acquisition systems,
where both high accuracy and fast sample rate are required.
Impulse Mode
Setting WARP = low and IMPULSE = high uses the lowest power
dissipation mode and allows power savings between conver-
sions. The maximum throughput in this mode is 450 kSPS, and
in this mode, the ADC powers down circuits after conversion,
making the AD7634 ideal for battery-powered applications.
TRANSFER FUNCTIONS
Except in 18-bit parallel interface mode, using the D0/OB/
2C
digital input or via the configuration register, the AD7634 offers
two output codings: straight binary and twos complement. See
Figure 26 and Table 8 for the ideal transfer characteristic and
digital output codes for the different analog input ranges, V
IN
.
Note that when using the configuration register, the D0/OB/
2C
input is a don’t care and should be tied to either high or low.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE (Straight Binary)
ANALOG INPUT
+FSR – 1.5 LSB
+FSR –1LSB–FSR + 1 LSB
–FSR
–FSR + 0.5 LSB
06406-026
Figure 26. ADC Ideal Transfer Function
Table 8. Output Codes and Ideal Input Voltages
V
REF
= 5 V Digital Output Code
Description
V
IN
= 0 V to +5 V
(10 V p-p)
V
IN
= 0 V to +10 V
(20 V p-p)
V
IN
= ±5 V
(20 V p-p)
V
IN
= ±10 V
(40 V p-p)
Straight Binary Twos Complement
FSR − 1 LSB +4.999962 V +9.999924 V +9.999924 V +19.999847 V 0x3FFFF
1
0x1FFFF
1
FSR − 2 LSB +4.999924 V +9.999847 V +9.999847 V +19.999695 V 0x3FFFE 0x1FFFE
Midscale + 1 LSB +38.15 µV −76.29 µV −76.29 µV +152.59 µV 0x20001 0x00001
Midscale 0 V 0 V 0 V 0 V 0x20000 0x00000
Midscale − 1 LSB −38.15 µV −76.29 µV −76.29 µV −152.59 µV 0x1FFFF 0x3FFFF
−FSR + 1 LSB −4.999962 V −9.999924 V −9.999924 V −19.999847 V 0x00001 0x20001
−FSR −5 V −10 V −10 V −20 V 0x00000
2
0x20000
2
1
This is also the code for overrange analog input.
2
This is also the code for underrange analog input.