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AD7321

Data Sheet

Rev. B | Page 28 of 36

MODES OF OPERATION

The AD7321 has several modes of operation that are designed

to provide flexible power management options. These options

are chosen to optimize the power dissipation/throughput rate

ratio for different application requirements. The mode of

operation of the AD7321 is controlled by the power management

bits, Bit PM1 and Bit PM0, in the control register as shown in

Table 11. The default mode is normal mode, where all internal

circuitry is fully powered up.

NORMAL MODE

(PM1 = PM0 = 0)

This mode is intended for the fastest throughput rate performance

with the AD7321 being fully powered up at all times. Figure 45

shows the general operation of the AD7321 in normal mode.

The conversion is initiated on the falling edge of CS, and the

track-and-hold section enters hold mode as described in the

Serial Interface section. Data on the DIN line during the

16 SCLK transfer is loaded into one of the on-chip registers if

the write bit is set. The register is selected by programming the

2 LEADING ZEROS, CHANNEL I.D. BIT, SIGN BIT

+ CONVERSION RESULT

DATA INTO CONTROL/RANGE REGISTER

SCLK

DOUT

DIN

Figure 45. Normal Mode

The AD7321 remains fully powered up at the end of the

conversion if both PM1 and PM0 contain 0 in the control

To complete the conversion and access the conversion result,

16 serial clock cycles are required. At the end of the conversion,

CS can idle either high or low until the next conversion.

Once the data transfer is complete, another conversion can be

initiated after the quiet time, tQUIET, has elapsed.

FULL SHUTDOWN MODE

(PM1 = PM0 = 1)

In this mode, all internal circuitry on the AD7321 is powered

down. The part retains information in the registers during full

shutdown. The AD7321 remains in full shutdown mode until

the power management bits, Bit PM1 and Bit PM0, in the

control register are changed.

A write to the control register with PM1 = 1 and PM0 = 1 places

the part into full shutdown mode. The AD7321 enters full shut-

down mode on the 15th SCLK rising edge once the control register

is updated.

If a write to the control register occurs while the part is in full

shutdown mode with the power management bits, Bit PM1 and

Bit PM0, set to 0 (normal mode), the part begins to power up

on the 15th SCLK rising edge once the control register is

updated. Figure 46 shows how the AD7321 is configured to exit

full shutdown mode. To ensure the AD7321 is fully powered up,

tPOWER-UP should elapse before the next CS falling edge.

SCLK

SDATA

DIN

INVALID DATA

CHANNEL IDENTIFIER BITS + CONVERSION RESULT

DATA INTO CONTROL REGISTER

tPOWER-UP

THE PART IS FULLY POWERED UP

ONCE

tPOWER-UP HAS ELAPSED

CONTROL REGISTER IS LOADED ON THE FIRST 15 CLOCKS,

PM1 = 0, PM0 = 0

TO KEEP THE PART IN NORMAL MODE, LOAD PM1 = PM0 = 0

IN CONTROL REGISTER

PART IS IN FULL

SHUTDOWN

PART BEGINS TO POWER UP ON THE 15TH

SCLK RISING EDGE AS PM1 = PM0 = 0

Figure 46. Exiting Full Shutdown Mode

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