DAC8564 datasheet(30/46 Pages) TI

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POWER-DOWN MODES

DAC Power-Down Commands

OUT

Amplifier

Resistor

String

DAC

Power-Down

Circuitry

Resistor

Network

DAC7565

SBAS412A – FEBRUARY 2008 – REVISED MARCH 2008 ............................................................................................................................................... www.ti.com

DACs. However, for the three power-down modes,

the supply current falls to 1.3

µA at 5.5V (0.5µA at

The DAC7565 has two separate sets of power-down

3.6V). Not only does the supply current fall, but the

commands. One set is for the DAC channels and the

output stage also switches internally from the output

other set is for the internal reference. For more

of the amplifier to a resistor network of known values.

information on powering down the reference, see the

Enable/Disable Internal Reference section.

The advantage of this switching is that the output

impedance of the device is known while it is in

power-down mode. As described in Table 7, there are

three different power-down options. VOUT can be

The DAC7565 uses four modes of operation. These

connected internally to GND through a 1k

Ω resistor, a

modes are accessed by setting three bits (PD2, PD1,

100k

Ω resistor, or open circuited (High-Z). The output

and PD0) in the shift register. Table 7 shows how to

stage is shown in Figure 96. In other words, DB16,

control the operating mode with data bits PD0

DB15, and DB14 = '111' represent a power-down

(DB16), PD1 (DB15), and PD2 (DB14).

condition with Hi-Z output impedance for a selected

channel. '101' represents a power-down condition

Table 7. DAC Operating Modes

with 1k

Ω output impedance, and '110' represents a

PD0

PD1

PD2

power-down condition with 100k

Ω output impedance.

(DB16)

(DB15)

(DB14)

DAC OPERATING MODES

Normal operation

Output typically 1k

Ω to GND

Output typically 100k

Ω to GND

Output high-impedance

The DAC7565 treats the power-down condition as

data; all the operational modes are still valid for

power-down. It is possible to broadcast a power-down

condition to all the DAC7565s in a system; it is also

possible to simultaneously power-down a channel

while updating data on other channels.

Figure 96. Output Stage During Power-Down

When the PD0 bit is set to '0', the device works

normally with its typical current consumption of 1mA

All analog channel circuitries are shut down when the

at 5.5V with an input code = 2048. The reference

power-down

mode

exercised.

However,

the

current is included with the operation of all four

contents of the DAC register are unaffected when in

power down. The time required to exit power-down is

typically 2.5

µs for V

DD = 5V, and 5µs for VDD = 3V.

See the Typical Characteristics for more information.

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