AD5024 Analog Devices, AD5024 Datasheet - Page 22

• Manufacturer Part Number: AD5024
• Manufacturer: Analog Devices

Specifications of AD5024

• Resolution (bits): 12bit
• Dac Update Rate: 125kSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5024/AD5044/AD5064
POWER-ON RESET
The AD5024/AD5044/AD5064/AD5064-1 contain a power-on
reset circuit that initializes the registers to their default values
and controls the output voltage during power-up. By connecting
the POR pin low, the AD5024/AD5044/AD5064/AD5064-1
output powers up to zero scale. Note that this is outside the
linear region of the DAC; by connecting the POR pin high, the
AD5024/AD5044/AD5064/AD5064-1 output powers up to
midscale. The output remains powered up at this level until a
valid write sequence is made to the DAC. This is useful in
applications where it is important to know the state of the
output of the DAC while it is in the process of powering up.
There is also a software executable reset function that resets the
DAC to the power-on reset code. Command 0111 is designated
for this reset function (see Table 8). Any events on LDAC or
CLR during power-on reset are ignored. The power-on reset
circuit is triggered when V
takes 50 μs to complete. No writes to the AD5024/AD5044/
AD5064/AD5064-1 should take place during this time. For
applications which have a slow V
more than 2 ms to 3ms), it is recommended that a software
reset command is written when the power supplies have
reached their final value.
POWER-DOWN MODES
The AD5024/AD5044/AD5064/AD5064-1 contain three
separate power-down modes. Command 0100 is designated for
the power-down function (see Table 8). These power-down
modes are software-programmable by setting two bits, Bit DB9
and Bit DB8, in the shift register. Table 12 shows how the state of
the bits corresponds to the mode of operation of the device.
Table 12. Modes of Operation
DB9
0
0
1
1
Table 13. 32-Bit Shift Register Contents for Power-Up/Power-Down Function
MSB
DB31
to
DB28
X
Don’t
cares
DB8
0
1
0
1
DB27
0
Command bits (C3 to C0)
Operating Mode
Normal operation
Power-down modes:
1 kΩ to GND
100 kΩ to GND
Three-state
DB26
1
DB25
0
DD
passes 2.6 V approximately and
DD
DB24
0
ramp time (for example,
DB23
X
Address bits (A3 to A0)—
DB22
X
don’t cares
DB21
X
Rev. E | Page 22 of 28
DB20
X
DB19
to
DB10
X
Don’t
cares
Any or all DACs (DAC D to DAC A) can be powered down to
the selected mode by setting the corresponding four bits (DB3,
DB2, DB1, DB0) to 1. See Table 13 for the contents of the shift
register during power-down/power-up operation.
When both Bit DB9 and Bit D8 in the shift register are set to 0,
the part works normally with its normal power consumption of
4 mA at 5 V. However, for the three power-down modes, the
supply current falls to 0.4 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 has the advantage that the output impedance of the part is
known while the part is in power-down mode. There are three
different power-down options. The output is connected inter-
nally to GND through either a 1 kΩ or a 100 kΩ resistor, or it is
left open-circuited (three-state). The output stage is illustrated in
Figure 51.
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. The DAC register can be
updated while the device is in power-down mode. The time to
exit power-down is typically 4.5 μs for V
DB9
PD1
down mode
DAC
Power-
Figure 51. Output Stage During Power-Down
DB8
PD0
POWER-DOWN
DB7
to
DB4
X
Don’t
cares
AMPLIFIER
CIRCUITRY
DB3
DAC D
Power-down/power-up channel
selection—set bit to 1 to select
DD
= 5 V (see Figure 30).
DB2
DAC C
RESISTOR
NETWORK
DB1
DAC B
V
OUT
LSB
DB0
DAC A