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AD5326 Datasheet(PDF) 16 Page - Analog Devices

Part No. AD5326
Description  2.5 V to 5.5 V, 500 μA, Quad Voltage Output 8-/10-/12-Bit DACs in 10-Lead Packages
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Manufacturer  AD [Analog Devices]
Direct Link  http://www.analog.com
Logo AD - Analog Devices

AD5326 Datasheet(HTML) 16 Page - Analog Devices

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AD5304/AD5314/AD5324
Data Sheet
Rev. H | Page 16 of 24
Double-Buffered Interface
The AD5304/AD5314/AD5324 DACs have double-buffered inter-
faces consisting of two banks of registers—input registers and
DAC registers. The input register is directly connected to the input
shift register and the digital code is transferred to the relevant input
register on completion of a valid write sequence. The DAC
register contains the digital code used by the resistor string.
Access to the DAC register is controlled by the LDAC bit. When
the LDAC bit is set high, the DAC register is latched and hence
the input register can change state without affecting the contents of
the DAC register. However, when the LDAC bit is set low, all DAC
registers are updated after a complete write sequence.
This is useful if the user requires simultaneous updating of all
DAC outputs. The user can write to three of the input registers
individually and then, by setting the LDAC bit low when
writing to the remaining DAC input register, all outputs
update simultaneously.
These parts contain an extra feature whereby the DAC register
is not updated unless its input register has been updated since
the last time that LDAC was brought low. Normally, when LDAC
is brought low, the DAC registers are filled with the contents of
the input registers. In the case of the AD5304/AD5314/AD5324,
the part updates the DAC register only if the input register has
been changed since the last time the DAC register was updated,
thereby removing unnecessary digital crosstalk.
POWER-DOWN MODE
The AD5304/AD5314/AD5324 have low power consumption,
dissipating only 1.5 mW with a 3 V supply and 3 mW with a
5 V supply. Power consumption can be further reduced when
the DACs are not in use by putting them into power-down mode,
selected by a 0 on Bit 13 (PD) of the control word.
When the PD bit is set to 1, all DACs work normally with a typical
power consumption of 600 μA at 5 V (500 μA at 3 V). However, in
power-down mode, the supply current falls to 200 nA at 5 V
(80 nA at 3 V) when all DACs are powered down. Not only does
the supply current drop, but also the output stage is internally
switched from the output of the amplifier, making it open-circuit.
This has the advantage that the output is three-stated while the
part is in power-down mode, and provides a defined input
condition for whatever is connected to the output of the DAC
amplifier. The output stage is illustrated in Figure 35.
The bias generator, the output amplifier, the resistor string, and
all other associated linear circuitry are shut down when the power-
down mode is activated. However, the contents of the registers
are unaffected when in power-down. The time to exit power-down
is typically 2.5 μs for VDD = 5 V and 5 μs when VDD = 3 V. This is
the time from the falling edge of the 16th SCLK pulse to when
the output voltage deviates from its power down voltage. See
Figure 22 for a plot.
RESISTOR
STRING DAC
AMPLIFIER
VOUT
POWER-DOWN
CIRCUITRY
Figure 35. Output Stage during Power-Down
MICROPROCESSOR INTERFACING
AD5304/AD5314/AD5324 to ADSP-21xx
Figure 36 shows a serial interface between the AD5304/AD5314/
AD5324 and the ADSP-21xx family. The ADSP-21xx is set up
to operate in the SPORT transmit alternate framing mode. The
ADSP-21xx sport is programmed through the SPORT control
register and must be configured as follows: internal clock operation,
active-low framing, and 16-bit word length. Transmission is
initiated by writing a word to the Tx register after the SPORT
has been enabled. The data is clocked out on each rising edge of
the DSP’s serial clock and clocked into the AD5304/AD5314/
AD5324 on the falling edge of the DAC’s SCLK.
AD5304/
AD5314/
AD5324*
ADSP-21xx*
*ADDITIONAL PINS OMITTED FOR CLARITY.
DIN
DT
SCLK
SCLK
SYNC
TFS
Figure 36. AD5304/AD5314/AD5324 to ADSP-21xx Interface


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