AD7654ASTZ datasheet(14/28 Pages) AD

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AD7654

Rev. B | Page 14 of 28

APPLICATION INFORMATION

CIRCUIT INFORMATION

The AD7654 is a very fast, low power, single-supply, precise,

simultaneous sampling 16-bit ADC.

The AD7654 provides the user with two on-chip, track-and-

hold, successive approximation ADCs that do not exhibit any

pipeline or latency, making it ideal for multiple multiplexed

channel applications. The AD7654 can also be used as a

4-channel ADC with two pairs simultaneously sampled.

The AD7654 can be operated from a single 5 V supply and be

interfaced to either 5 V or 3 V digital logic. It is housed in a

48-lead LQFP or tiny 48-lead LFCSP that combines space

savings and allows flexible configurations as either a serial or

parallel interface. The AD7654 is pin-to-pin compatible with

PulSAR ADCs.

MODES OF OPERATION

The AD7654 features two modes of operation, normal and

impulse. Each of these modes is more suitable for specific

applications.

Normal mode is the fastest mode (500 kSPS). Except when it is

powered down (PD = HIGH), the power dissipation is almost

independent of the sampling rate.

Impulse mode, the lowest power dissipation mode, allows

power saving between conversions. The maximum

throughput in this mode is 444 kSPS. When operating at

10 kSPS, for example, it typically consumes only 2.6 mW. This

feature makes the AD7654 ideal for battery-powered

applications.

TRANSFER FUNCTIONS

The AD7654 data format is straight binary. The ideal transfer

characteristic for the AD7654 is shown in Figure 17 and Table 7.

The LSB size is 2*VREF/65536, which is about 76.3 μV.

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

+FS – 1.5 LSB

+FS – 1 LSB

–FS + 1 LSB

–FS

–FS + 0.5 LSB

Figure 17. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

Description

Analog Input

VREF = 2.5 V

Digital Output Code

FSR − 1 LSB

4.999924 V

0xFFFF1

FSR − 2 LSB

4.999847 V

0xFFFE

Midscale + 1 LSB

2.500076 V

0x8001

Midscale

2.5 V

0x8000

Midscale − 1 LSB

2.499924 V

0x7FFF

−FSR + 1 LSB

−76.29 μV

0x0001

−FSR

0 V

0x00002

1 This is also the code for overrange analog input

(VINx – VINxN above 2 × (VREF − VREFGND)).

2 This is also the code for underrange analog input (VINx below VINxN).

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