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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, VIN.

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

ANALOG INPUT

+FSR – 1.5 LSB

+FSR –1LSB

–FSR + 1 LSB

–FSR

–FSR + 0.5 LSB

Figure 26. ADC Ideal Transfer Function

Table 8. Output Codes and Ideal Input Voltages

VREF = 5 V

Digital Output Code

Description

VIN = 0 V to +5 V

(10 V p-p)

VIN = 0 V to +10 V

(20 V p-p)

VIN = ±5 V

(20 V p-p)

VIN = ±10 V

(40 V p-p)

Straight Binary

Twos Complement

FSR − 1 LSB

+4.999962 V

+9.999924 V

+19.999847 V

0x3FFFF1

0x1FFFF1

FSR − 2 LSB

+4.999924 V

+9.999847 V

+19.999695 V

0x3FFFE

0x1FFFE

Midscale + 1 LSB

+38.15 μV

−76.29 μV

+152.59 μV

0x20001

0x00001

Midscale

0 V

0x20000

0x00000

Midscale − 1 LSB

−38.15 μV

−76.29 μV

−152.59 μV

0x1FFFF

0x3FFFF

−FSR + 1 LSB

−4.999962 V

−9.999924 V

−19.999847 V

0x00001

0x20001

−FSR

−5 V

−10 V

−20 V

0x000002

0x200002

1 This is also the code for overrange analog input.

2 This is also the code for underrange analog input.

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