AD7951 Analog Devices, AD7951 Datasheet - Page 18

• Manufacturer Part Number: AD7951
• Manufacturer: Analog Devices

Specifications of AD7951

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 1MSPS
• Interface: Byte,Par,Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni
• Ain Range: Bip 10V,Bip 5.0V,Uni 10V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7951
MODES OF OPERATION
The AD7951 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 allows the fastest
conversion rate up to 1 MSPS. 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 AD7951 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 (800 kSPS) without any limitation on
time between conversions. This mode makes the AD7951 ideal
for asynchronous applications such as data acquisition systems,
where both high accuracy and fast sample rate are required.
Table 7. 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
This is also the code for overrange analog input (V
V
4.999695 V
4.999390 V
2.500305 V
2.5 V
2.499695 V
305.2 μV
0 V
IN
= 5 V
V
9.999389 V
9.998779 V
5.000610 V
5.000000 V
4.999389 V
610.4 μV
0 V
IN
IN+
IN+
= 10 V
− V
− V
IN−
IN−
above V
below V
V
REF
= 5 V
REF
REF
V
+4.999389 V
+4.998779 V
+610.4 μV
0 V
−610.4 μV
−4.999389 V
−5 V
IN
− V
− V
= ±5 V
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REFGND
REFGND
).
).
+9.998779 V
+9.997558 V
−1.221 mV
V
+1.221 mV
0 V
−9.998779 V
−10 V
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 670 kSPS and in this
mode, the ADC powers down circuits after conversion making
the AD7951 ideal for battery-powered applications.
TRANSFER FUNCTIONS
Using the OB/ 2C digital input or via the configuration register,
the AD7951 offers two output codings: straight binary and twos
complement. See Figure 26 and Table 7 for the ideal transfer
characteristic and digital output codes for the different analog
input ranges, V
register, the OB/ 2C input is a don’t care and should be tied to
either high or low.
IN
= ±10 V
111...111
111...110
111...101
000...010
000...001
000...000
–FSR + 0.5 LSB
–FSR
IN
Figure 26. ADC Ideal Transfer Function
. Note that when using the configuration
Straight Binary
0x3FFF
0x3FFE
0x2001
0x2000
0x1FFF
0x0001
0x0000
–FSR + 1 LSB
1
2
ANALOG INPUT
Digital Output Code
+FSR – 1.5 LSB
Twos Complement
0x1FFF
0x1FFE
0x0001
0x0000
0x3FFF
0x2001
0x2000
1
2
+FSR – 1 LSB