AD7816ARM datasheet(15/20 Pages) AD

15 / 20 page

REV. C

AD7816/AD7817/AD7818

–15–

THROUGHPUT – kHz

0.01

080

0.1

Figure 19. Power vs. Throughput Rate

AD7817 SERIAL INTERFACE

The serial interface on the AD7817 is a 5-wire interface with

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

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.

DB7 – DB0

DB7(DB9) – DB0

DOUT

CONVST

SCLK

BUSY

RD/

DIN

OTI

t15

t16

tPOWER-UP

Figure 17. Mode 2 Operation

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 this data sheet).

tPOWER-UP tCONVERT

CONVST

BUSY

2 s

8 s

tCYCLE

100 s @ 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 4.8 mW, VDD = 3 V. If the power up time is

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

dissipate 4.8 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 while powered up dur-

ing each cycle is (11/100)

× (4.8 mW) = 528 µW typ. Power

dissipated while powered down during each cycle is (89/100)

(3 V

× 2 µA) = 5.34 µW typ. Overall power dissipated is 528 µW

+ 5.34

µW = 533 µW.

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