Linear Technology DC1333A-C - LTC2640-HM12: 12-Bit SPI DAC (4.096V ref, Reset to Mid-Scale), req DC590 DC1333A-C DC1333A-C Data Sheet
Product codes
DC1333A-C
LTC2640
17
2640fc
The LTC2640 is a family of single voltage-output DACs
in 8-lead ThinSOT packages. Each DAC can operate rail-
to-rail using an external reference, or with its full-scale
voltage set by an integrated reference. 12 combinations of
accuracy (12-, 10-, and 8-bit), power-on reset value (zero
or mid-scale), and full-scale voltage (2.5V or 4.096V) are
available. The LTC2640 is controlled using a 3-wire SPI/
MICROWIRE compatible interface.
Power-On Reset
The LTC2640-HZ/LTC2640-LZ clear the output to zero-
The LTC2640-HZ/LTC2640-LZ clear the output to zero-
scale when power is first applied, making system initializa-
tion consistent and repeatable.
For some applications, downstream circuits are active
For some applications, downstream circuits are active
during DAC power-up, and may be sensitive to nonzero
outputs from the DAC during this time. The LTC2640
contains circuitry to reduce the power-on glitch: the
analog output typically rises less than 5mV above zero-
scale during power on if the power supply is ramped
to 5V in 1ms or more. In general, the glitch amplitude
decreases as the power supply ramp time is increased.
See “Power-On Reset Glitch” in the Typical Performance
Characteristics section.
The LTC2640-HM/LTC2640-LM provide an alternative
reset, setting the output to mid-scale when power is first
applied.
Default reference mode selection is described in the Refer-
Default reference mode selection is described in the Refer-
ence Modes section.
Power Supply Sequencing
The voltage at REF (Pin 6) should be kept within the range
The voltage at REF (Pin 6) should be kept within the range
–0.3V ≤ V
REF
≤ V
CC
+ 0.3V (see Absolute Maximum Rat-
ings). Particular care should be taken to observe these
limits during power supply turn-on and turn-off sequences,
when the voltage at V
CC
(Pin 5) is in transition.
Transfer Function
The digital-to-analog transfer function is:
The digital-to-analog transfer function is:
V
OUT(IDEAL)
=
k
2
N
V
REF
where k is the decimal equivalent of the binary DAC input
code, N is the resolution, and V
REF
is either 2.5V (LTC2640-
LM/LTC2640-LZ) or 4.096V (LTC2640-HM/LTC2640-HZ)
when in Internal Reference mode, and the voltage at REF
(Pin 6) when in External Reference mode.
operation
Figure 2. Command and Data Input Format
2640 F02
C3
COMMAND
4 DON'T-CARE BITS
MSB
MSB
MSB
LSB
LSB
LSB
DATA (12 BITS + 4 DON'T-CARE BITS)
C2
C1
C0
X
X
X
X
D11 D10 D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
X
X
C3
COMMAND
4 DON'T-CARE BITS
DATA (10 BITS + 6 DON'T-CARE BITS)
C2
C1
C0
X
X
X
X
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
X
X
X
X
C3
COMMAND
INPUT WORD (LTC2640-12)
INPUT WORD (LTC2640-10)
INPUT WORD (LTC2640-8)
4 DON'T-CARE BITS
DATA (8 BITS + 8 DON'T-CARE BITS)
C2
C1
C0
X
X
X
X
D7
D6
D5
D4
D3
D2
D1
D0
X
X
X
X
X
X
X
X