AD7818AR(2000) Просмотр технического описания (PDF) - Analog Devices

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AD7818AR
(Rev.:2000)

Single- and 4-Channel, 9 μ
s, 10-Bit ADCs with On-Chip Temperature Sensor

Analog Devices 

AD7816/AD7817/AD7818

CONVST

BUSY

t POWER-UP

t1

t3

CS

OTI

RD/ WR

t15

t16

SCLK

DIN

DOUT

DB0 – DB7

Figure 17. Mode 2 Operation

DB0 – DB7(DB9)

POWER VS. THROUGHPUT

Superior power performance can be achieved by using the Auto-

matic Power-Down (Mode 2) at the end of a conversion—see

Operating Modes section of the data sheet.

CONVST

tPOWER-UP tCONVERT

2␮s

8␮s

BUSY

tCYCLE

100ms @ 10kSPS

Figure 18. Automatic Power-Down

Figure 18 shows how the Automatic Power-Down is imple-

mented to achieve the optimum power performance from the

AD7816, AD7817 and AD7818. The devices are operated in

Mode 2 and the duration of CONVST pulse is set to be equal to

the power-up time (2 µs). As the throughput rate of the device is

reduced the device remains in its power-down state longer, and

the average power consumption over time drops accordingly.

For example, if the AD7817 is operated in a continuous sam-

pling mode with a throughput rate of 10 kSPS, the power con-

sumption is calculated as follows. The power dissipation during

normal operation is 6 mW, VDD = 3 V. If the power up time is

2 µs and the conversion time is 9 µs, the AD7817 can be said to

dissipate 6 mW typically for 11 µs (worst case) during each

conversion cycle. If the throughput rate is 10 kSPS, the cycle

time is 100 µs and the power dissipated during each cycle is

(11/100) × (6 mW) = 600 µW typ.

10

1

0.1

0.01

0

10 20 30 40 50

60 70 80

THROUGHPUT – kHz

Figure 19. Power vs. Throughput Rate

AD7817 SERIAL INTERFACE

The serial interface on the AD7817 is a five-wire interface with

read and write capabilities, with data being read from the output

register via the DOUT line and data being written to the control

register via the DIN line. The part operates in a slave mode and

requires an externally applied serial clock to the SCLK input to

access data from the data register or write to the control byte.

The RD/WR line is used to determine whether data is being

written to or read from the AD7817. When data is being written

to the AD7817, the RD/WR line is set logic low and when data

is being read from the part the line is set logic high—see Figure

20. The serial interface on the AD7817 is designed to allow the

part to be interfaced to systems that provide a serial clock that is

synchronized to the serial data, such as the 80C51, 87C51,

68HC11, 68HC05 and PIC16Cxx microcontrollers.

–14–

REV. A

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