AD7621 datasheet(18/32 Pages) AD

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AD7612

Rev. 0 | 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, VIN. 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

ANALOG INPUT

+FSR – 1.5 LSB

+FSR –1LSB

–FSR + 1 LSB

–FSR

–FSR + 0.5 LSB

Figure 26. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

VREF = 5 V

Digital Output Code

Description

VIN = 5 V

VIN = 10 V

VIN = ±5 V

VIN = ±10 V

Straight Binary

Twos Complement

FSR − 1 LSB

4.999924 V

9.999847 V

+4.999847 V

+9.999695 V

0xFFFF1

0x7FFF1

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

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

−5 V

−10 V

0x00002

0x80002

1 This is also the code for overrange analog input (VIN+ − VIN− above VREF − VREFGND).

2 This is also the code for overrange analog input (VIN+ − VIN− below VREF − VREFGND).

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