AD5313R datasheet(20/26 Pages) AD

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AD5313R

Data Sheet

Rev. B | Page 20 of 26

27B

READBACK OPERATION

Readback mode is invoked through a software executable readback

command. If the SDO output is disabled via the daisy-chain mode

disable bit in the control register, it is automatically enabled for

the duration of the read operation, after which it is disabled again.

Command 1001 is reserved for the readback function. This com-

mand, in association with selecting one of the address bits, DAC B

or DAC A, determines the register to be read. Note that only one

DAC register can be selected during readback. The remaining

three address bits (which includes the two don’t care bits) must

be set to Logic 0. The remaining data bits in the write sequence

are ignored. If more than one address bit is selected or no address

bits are selected, DAC Channel A is read back by default. During

the next SPI write, the data appearing on the SDO output contains

the data from the previously addressed register.

For example, to read back the DAC register for Channel A,

implement the following sequence:

1. Write 0x900000 to the AD5313R input register. This setting

configures the device for read mode with the Channel A

DAC register selected. Note that all data bits, DB15 to DB0,

are don’t care bits.

2. Follow this write operation with a second write, a NOP

condition, 0x000000 (0xF00000 in daisy-chain mode).

During this write, the data from the register is clocked out

on the SDO line. DB23 to DB20 contain undefined data,

and the last 16 bits contain the DB19 to DB4 DAC register

contents.

28B

POWER-DOWN OPERATION

The AD5313R contains three separate power-down modes.

Command 0100 controls the power-down function (see Table 9).

These power-down modes are software-programmable by

setting eight bits, Bit DB7 to Bit DB0, in the input shift register.

There are two bits associated with each DAC channel. Table 11

explains how the state of the two bits corresponds to the mode

of operation of the device.

Table 11. Modes of Operation

Operating Mode

PDx1

PDx0

Normal Operation Mode

Power-Down Modes

1 kΩ to GND

100 kΩ to GND

Three-State

Either DAC or both DACs (DAC A and DAC B) can be powered

down to the selected mode by setting the corresponding bits. See

Table 12 for the contents of the input shift register during the

power-down/power-up operation.

When both Bit PDx1 and Bit PDx0 (where x is the channel that

is selected) in the input shift register are set to 0, the AD5313R

works normally, with a normal power consumption of 4 mA at

5 V. However, for the three power-down modes of the AD5313R,

the supply current falls to 4 μA at 5 V. Not only does the supply

current fall, but the output stage is also internally switched from

the output of the amplifier to a resistor network of known values.

This switchover has the advantage that the output impedance of

the part is known while the part is in power-down mode. The

three power-down options are as follows:

•

The output is connected internally to GND through a 1 kΩ

resistor.

•

The output is connected internally to GND through a 100 kΩ

resistor.

•

The output is left open-circuited (three-state).

The output stage is illustrated in Figure 42.

Figure 42. Output Stage During Power-Down

The bias generator, output amplifier, resistor string, and other

associated linear circuitry are shut down when the power-down

mode is activated. However, the contents of the DAC register

are unaffected when in power-down, and the DAC register can

be updated while the device is in power-down mode. The time

that is required to exit power-down is typically 4.5 µs for VDD = 5 V.

To further reduce the current consumption, the on-chip reference

can be powered off (see the Internal Reference Setup section).

Table 12. 24-Bit Input Shift Register Contents of Power-Down/Power-Up Operation

15F

DB23

(MSB)

DB22

DB21

DB20

DB19 to DB16

DB15 to DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

(LSB)

PDB1

PDB0

PDA1

PDA0

Command bits (C3 to C0)

Address bits; don’t care

Power-down,

select DAC B

Set to 1

Power-down,

select DAC A

X = don’t care.

RESISTOR

NETWORK

VOUTX

DAC

POWER-DOWN

CIRCUITRY

AMPLIFIER

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