AD7440BRTZ-R2 datasheet(25/27 Pages) AD

25 / 27 page

Data Sheet

AD7440/AD7450A

Rev. D | Page 25 of 27

Thus, the average power dissipated during each cycle with a

throughput rate of 100 kSPS is (2/10) × 4 mW = 0.8 mW.

This is how the power numbers in Figure 44 are calculated.

For throughput rates above 320 kSPS, it is recommended to

reduce the serial clock frequency for best power performance.

Figure 44. Power vs. Throughput Rate for Power-Down Mode

GROUNDING AND LAYOUT HINTS

The printed circuit board that houses the AD7440/AD7450A

should be designed so that the analog and digital sections are

separated and confined to certain areas of the board. This

facilitates the use of ground planes that can be easily separated.

A minimum etch technique is generally best for ground planes

as it gives the best shielding. Digital and analog ground planes

should be joined in only one place, a star ground point

established as close to the GND pin on the AD7440/AD7450A

as possible. Avoid running digital lines under the devices

because this couples noise onto the die. The analog ground

plane should be allowed to run under the AD7440/AD7450A to

avoid noise coupling. The power supply lines to the AD7440/

AD7450A should use as large a trace as possible to provide low

impedance paths and reduce the effects of glitches on the power

supply line.

Fast switching signals like clocks should be shielded with digital

ground to avoid radiating noise to other sections of the board,

and clock signals should never run near the analog inputs.

Avoid crossover of digital and analog signals. Traces on

opposite sides of the board should run at right angles to each

other. This reduces the effects of feedthrough through the

board. A microstrip technique is by far the best but is not

always possible with a double-sided board.

In this technique, the component side of the board is dedicated

to ground planes while signals are placed on the solder side.

Good decoupling is also important. All analog supplies should

be decoupled with 10 µF tantalum capacitors in parallel with

0.1 µF capacitors to GND. To achieve the best from these

decoupling components, they must be placed as close as

possible to the device.

EVALUATING THE AD7440/AD7450A

PERFORMANCE

The evaluation board package includes a fully assembled and

tested evaluation board, documentation, and software for

controlling the board from a PC via the evaluation board

controller. The evaluation board controller can be used in

conjunction with the AD7440/AD7450A evaluation board, as

well as many other Analog Devices evaluation boards ending

with the CB designator, to demonstrate and evaluate the ac and

dc performance of the AD7440/AD7450A.

The software allows the user to perform ac (fast Fourier

transform) and dc (histogram of codes) tests on the device. See

the AD7440/AD7450A application note that accompanies the

evaluation kit for more information.

THROUGHPUT (kSPS)

100

350

0.01

100

150

200

250

300

0.1

VDD = 5V

VDD = 3V

AD7440BRTZ-R2 数据表(PDF) 25 Page - Analog Devices

AD7440BRTZ-R2 数据表(HTML) 25 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

数据表下载