Datasheet

AD7612 Data Sheet
Rev. A | Page 18 of 32
MODES OF OPERATION
The AD7612 features three modes of operation: warp, normal,
and impulse. Each of these modes is more suitable to specific
applications. The mode is configured with the input pins, WARP
and IMPULSE, or via the configuration register. See Table 6 for
the pin details and the Hardware Configuration section and
Software Configuration section for programming the mode
selection with either pins or configuration register. Note that
when using the configuration register, the WARP and IMPULSE
inputs are don’t cares and should be tied to either high or low.
Warp Mode
Setting WARP = high and IMPULSE = low allow the fastest con-
version rate up to 750 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 since 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 AD7612 ideal for applications
where both high accuracy and fast sample rate are required. In
addition, the AD7612 can run up to 900 kSPS throughput with
some performance degradation, mainly dc linearity.
Normal Mode
Setting WARP = IMPULSE = low or WARP = IMPULSE = high
allows the fastest mode (600 kSPS) without any limitation on
time between conversions. This mode makes the AD7612 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 saving between conversions.
The maximum throughput in this mode is 500 kSPS and in this
mode, the ADC powers down circuits after conversion making
the AD7612 ideal for battery-powered applications.
TRANSFER FUNCTIONS
Using the OB/
2C
digital input or via the configuration register,
the AD7612 offers two output codings: straight binary and twos
complement. See Figure 26 and Table 7 for the ideal transfer char-
acteristic and digital output codes for the different analog input
ranges, V
IN
. Note that when using the configuration register, the
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
06265-026
Figure 26. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
V
REF
= 5 V Digital Output Code
Description V
IN
= 5 V V
IN
= 10 V V
IN
= ±5 V V
IN
= ±10 V Straight Binary Twos Complement
FSR − 1 LSB 4.999924 V 9.999847 V +4.999847 V +9.999695 V 0xFFFF
1
0x7FFF
1
FSR − 2 LSB 4.999847 V 9.999695 V +4.999695 V +9.999390 V 0xFFFE 0x7FFE
Midscale + 1 LSB 2.500076 V 5.000153 V +152.6 µV +305.2 µV 0x8001 0x0001
Midscale 2.5 V 5.000000 V 0 V 0 V 0x8000 0x0000
Midscale − 1 LSB 2.499924 V 4.999847 V −152.6 µV −305.2 µV 0x7FFF 0xFFFF
−FSR + 1 LSB 76.3 µV 152.6 µV −4.999847 V −9.999695 V 0x0001 0x8001
−FSR 0 V 0 V −5 V −10 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 overrange analog input (V
IN+
− V
IN−
below V
REF
− V
REFGND
).