REV. 0

–10–

AD7482

Thus, the power dissipated during each cycle is:

27

42

69

mW

mW

mW

+=

Figure 7 shows the AD7482 conversion sequence operating in

normal mode.

CONVST

BUSY

1 s

300 ns

700 ns

Figure 7. Normal Mode Power Dissipation

In NAP Mode, almost all the internal circuitry is powered down.

In this mode, the power dissipation of the AD7482 is reduced

to 2.5 mW. When exiting NAP Mode, a minimum of 300 ns

when using an external reference must be waited before initiat-

ing a conversion. This is necessary to allow the internal

circuitry to settle after power-up and for the track-and-hold to

properly acquire the analog input signal. The internal reference

cannot be used in conjunction with the NAP Mode.

If the AD7482 is put into NAP Mode after each conversion, the

average power dissipation will be reduced, but the throughput rate

will be limited by the power-up time. Using the AD7482 with a

throughput rate of 500 kSPS while placing the part in NAP

Mode after each conversion would result in average power dissi-

pation as follows:

The power-up phase contributes:

() (

)

300

2

5

12

ns/

s

V

mA

9 mW

µ×

×

=

The conversion phase contributes:

(/

) (

)

.

300

2

5

18

13 5

ns

s

V

mA

mA

µ×

×

=

While in NAP Mode for the rest of the cycle, the AD7482

dissipates only 1.75 mW of power.

() (

.

)

.

1400

2

5

0 5

1 75

ns/

s

V

mA

mW

µ×

×

=

Thus, the power dissipated during each cycle is:

913 51 75

24 25

mW +

. mW + .

mW =

mW

.

Figure 8 shows the AD7482 conversion sequence if putting the

part into NAP Mode after each conversion.

CONVST

600ns

NAP

BUSY

1400ns

300ns

2

s

Figure 8. NAP Mode Power Dissipation

Figures 9 and 10 show a typical graphical representation of

power versus throughput for the AD7482 when in normal and

NAP Modes, respectively.

THROUGHPUT – kSPS

90

0

3000

500

1500

2000

2500

85

80

75

70

65

60

1000

Figure 9. Normal Mode, Power vs. Throughput

THROUGHPUT – kSPS

0

0

250

500

750

1000

1250

1500

1750

2000

10

20

30

40

50

60

70

80

90

Figure 10. NAP Mode, Power vs. Throughput

In Standby Mode, all the internal circuitry is powered down and

the power consumption of the AD7482 is reduced to 10

µW. The

power-up time necessary before a conversion can be initiated is

longer because more of the internal circuitry has been powered

down. In using the internal reference of the AD7482, the ADC

must be brought out of Standby Mode 500 ms before a conver-

sion is initiated. Initiating a conversion before the required

power-up time has elapsed will result in incorrect conversion

data. If an external reference source is used and kept powered

up while the AD7482 is in Standby Mode, the power-up time

required will be reduced to 80 s.