Datasheet

ADC081S051

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SNAS309E –APRIL 2005–REVISED MARCH 2013

To enter shutdown mode, a conversion must be interrupted by bringing CS high anytime between the second

and tenth falling edges of SCLK, as shown in Figure 23. 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.

Figure 23. Entering Shutdown Mode

Figure 24. Entering Normal Mode

To exit shutdown mode, bring CS back low. Upon bringing CS low, the ADC will begin powering up (power-up

time is specified in the Timing Specifications table). 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 24.

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 ADC will be fully

powered-up after 16 SCLK cycles.

POWER MANAGEMENT

The ADC takes time to power-up, either after first applying V

, 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 conversion, the ADC will perform conversions properly. Note that the t

QUIET

time

must still be included between the first dummy conversion and the second valid conversion.

When the V

supply is first applied, the ADC may power up in either of the two modes: normal or shutdown. As

such, one dummy conversion should be performed after start-up, as described in the previous paragraph. The

part may then be placed into either normal mode or the shutdown mode, as described in Sections 7.1 and 7.2.

When the ADC is operated continuously in normal mode, the maximum specified throughput is f

SCLK

/ 20 at the

maximum specified f

SCLK

. Throughput may be traded for power consumption by running f

SCLK

at its maximum

specified rate and performing fewer conversions per unit time, raising the ADC CS line after the 10th and before

the 15th fall of SCLK of each conversion. A plot of typical power consumption versus throughput is shown in the

Typical Performance Characteristics section. To calculate the power consumption for a given throughput, multiply

the fraction of time spent in the normal mode by the normal mode power consumption and add the fraction of

time spent in shutdown mode multiplied by the shutdown mode power consumption. Note that the curve of power

consumption vs. throughput is essentially linear. This is because the power consumption in the shutdown mode

is so small that it can be ignored for all practical purposes.

Product Folder Links: ADC081S051