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DAC8408FS View Datasheet(PDF) - Analog Devices

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Description
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DAC8408FS Datasheet PDF : 16 Pages
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DAC8408
Figure 4. Equivalent DAC Circuit (AII Digital Inputs LOW)
DIGITAL SECTION
Figure 5 shows the digital input/output structure for one bit.
The digital WR, WR, and RD controls shown in the figure are
internally generated from the external A/B, R/W, DS1, and DS2
signals. The combination of these signals decide which DAC is
selected. The digital inputs are CMOS inverters, designed such
that TTL input levels (2.4 V and 0.8 V) are converted into
CMOS logic levels. When the digital input is in the region of 1.2 V
to 1.8 V, the input stages operate in their linear region and draw
current from the +5 V supply (see Typical Supply Current vs.
Logic Level curve on page 6). It is recommended that the digital
input voltages be as close to VDD and DGND as is practical in
order to minimize supply currents. This allows maximum sav-
ings in power dissipation inherent with CMOS devices. The
three-state readback digital output drivers (in the active mode)
provide TTL-compatible digital outputs with a fan-out of one
TTL load. The three state digital readback leakage-current is
typically 5 nA.
Figure 5. Digital Input/Output Structure
INTERFACE LOGIC SECTION
DAC Operating Modes
• All DACs in HOLD MODE.
• DAC A, B, C, or D individually selected (WRITE MODE).
• DAC A, B, C, or D individually selected (READ MODE).
• DACs A and C simultaneously selected (WRITE MODE).
• DACs B and D simultaneously selected (WRITE MODE).
DAC Selection: Control inputs, DS1, DS2, and A/B select
which DAC can accept data from the input port (see Mode Se-
lection Table).
Mode Selection: Control inputs DS and R/W control the oper-
ating mode of the selected DAC.
Write Mode: When the control inputs DS and R/W are both
low, the selected DAC is in the write mode. The input data
latches of the selected DAC are transparent, and its analog out-
put responds to activity on the data inputs DB0–DB7.
Hold Mode: The selected DAC latch retains the data that was
present on the bus line just prior to DS or R/W going to a high
state. All analog outputs remain at the values corresponding to
the data in their respective latches.
Read Mode: When DS is low and R/W is high, the selected
DAC is in the read mode, and the data held in the appropriate
latch is put back onto the data bus.
MODE SELECTION TABLE
Control Logic
DS1 DS2 A/B R/W
Mode
L
HH L
L
HL L
H
LH L
H
LL
L
WRITE
WRITE
WRITE
WRITE
L
HH H
L
HL H
H
LH H
H
LL
H
READ
READ
READ
READ
L
LH L
L
LL L
WRITE
WRITE
H
HX X
L
LH H
L
LL H
HOLD
HOLD
HOLD
L = Low State, H = High State, X = Irrelevant
DAC
A
B
C
D
A
B
C
D
A&C
B&D
A/B/C/D
A/B/C/D
A/B/C/D
REV. A
–9–
 

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