ADC101S101EVAL datasheet(20/23 Pages) NSC

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Applications Information (Continued)

9.0 SHUTDOWN MODE

Shutdown mode is appropriate for applications that either do

not sample continuously, or are willing to trade throughput

for power consumption. When the ADC121S101/101S101/

081S101 is in shutdown mode, all of the analog circuitry is

turned off.

To enter shutdown mode, a conversion must be interrupted

by bringing CS back high anytime between the second and

tenth falling edges of SCLK, as shown in Figure 10. Once CS

has been brought high in this manner, the device will enter

shutdown mode; the current conversion will be aborted and

SDATA will enter TRI-STATE. If CS is brought high before the

second falling edge of SCLK, the device will not change

mode; this is to avoid accidentally changing mode as a result

of noise on the CS line.

10.0 EXITING SHUTDOWN MODE

To exit shutdown mode, bring CS back low. Upon bringing

CS low, the ADC121S101/101S101/081S101 will begin pow-

ering up. Power up typically takes 1 µs. This microsecond of

power-up delay results in the first conversion result being

unusable. The second conversion performed after power-up,

however, is valid, as shown in Figure 11.

If CS is brought back high before the 10th falling edge of

SCLK, the device will return to shutdown mode. This is done

to avoid accidentally entering normal mode as a result of

noise on the CS line. To exit shutdown mode and remain in

normal mode, CS must be kept low until after the 10th falling

edge of SCLK. The ADC121S101/101S101/081S101 will be

fully powered-up after 16 SCLK cycles.

11.0 POWER-UP TIMING

The ADC121S101/101S101/081S101 typically requires 1 µs

to power up, either after first applying V

DD, or after returning

to normal mode from shutdown mode. This corresponds to

one "dummy" conversion for any SCLK frequency within the

specifications in this document. After this first dummy con-

version, the ADC121S101/101S101/081S101 will perform

conversions properly. Note that the t

QUIET time must still be

included between the first dummy conversion and the sec-

ond valid conversion.

12.0 STARTUP MODE

When the V

DD supply is first applied, the ADC121S101/

101S101/081S101 may power up in either of the two modes:

normal or shutdown. As such, one dummy conversion

should be performed after start-up, exactly as described in

Section 11.0. The part may then be placed into either normal

mode or the shutdown mode, as described in Sections 8.0

and 9.0.

13.0 POWER MANAGEMENT

When the ADC121S101/101S101/081S101 is operated con-

tinuously in normal mode, throughput up to 1 MSPS can be

achieved. The user may trade throughput for power con-

sumption by simply performing fewer conversions per unit

time, and putting the ADC121S101/101S101/081S101 into

shutdown mode between conversions. This method is not

advantageous beyond 350 kSPS throughput.

A plot of maximum power consumption versus throughput is

shown in Figure 12 below. To calculate the power consump-

tion for a given throughput, remember that each time the part

exits shutdown mode and enters normal mode, one dummy

conversion is required. Generally, the user will put the part

into normal mode, execute one dummy conversion followed

by one valid conversion, and then put the part back into

shutdown mode. When this is done, the fraction of time

20110216

FIGURE 11. Entering Shutdown Mode

20110217

FIGURE 12. Entering Normal Mode

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