Datasheet

LTC2636
17
2636fb
operation
The LTC2636 is a family of octal voltage output DACs
in 14-lead DFN and 16-lead MSOP packages. Each DAC
can operate rail-to-rail using an external reference, or
with its full-scale voltage set by an integrated reference.
Eighteen combinations of accuracy (12-, 10-, and 8-bit),
power-on reset value (zero-scale, mid-scale in internal
reference mode, or mid-scale in external reference mode),
and full-scale voltage (2.5V or 4.096V) are available. The
LTC2636 is controlled using a 3-wire SPI/MICROWIRE
compatible interface.
Power-On Reset
The LTC2636-HZ/-LZ clear the output to zero-scale when
power is first applied, making system initialization con-
sistent and repeatable.
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 LTC2636
contains circuitry to reduce the power-on glitch: the
analog output typically rises less than 5mV above zero-
scale during power on. 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 LTC2636-HMI/-HMX/-LMI/-LMX provide an alterna-
tive reset, setting the output to mid-scale when power is
first applied. The LTC2636-LMI and LTC2636-HMI power
up in internal reference mode, with the output set to a
mid-scale voltage of 1.25V and 2.048V respectively. The
LTC2636-LMX and LTC2636-HMX power-up in external
reference mode, with the output set to mid-scale of the
external reference. Default reference mode selection is
described in the Reference Modes section.
Power Supply Sequencing
The voltage at REF (Pin 9-DFN, Pin 11-MSOP) must be
kept within the range –0.3V ≤ V
REF
≤ V
CC
+ 0.3V (see
Absolute Maximum Ratings). Particular care should be
taken to observe these limits during power supply turn-
on and turn-off sequences, when the voltage at V
CC
is in
transition.
Transfer Function
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 (LTC2636-
LMI/-LMX/-LZ) or 4.096V (LTC2636-HMI/-HMX/-HZ) when
in Internal Reference mode, and the voltage at REF when
in External Reference mode.
Table 1. Command Codes
COMMAND*
C3 C2 C1 C0
0 0 0 0 Write to Input Register n
0 0 0 1 Update (Power-Up) DAC Register n
0 0 1 0 Write to Input Register n, Update (Power-Up) All
0 0 1 1 Write to and Update (Power-Up) DAC Register n
0 1 0 0 Power-Down DAC n
0 1 0 1 Power-Down Chip (All DAC’s and Reference)
0 1 1 0 Select Internal Reference (Power-Up Reference)
0 1 1 1 Select External Reference (Power-Down Internal
Reference)
1 1 1 1 No Operation
*Command codes not shown are reserved and should not be used.
Table 2. Address Codes
ADDRESS (n)*
A3 A2 A1 A0
0 0 0 0 DAC A
0 0 0 1 DAC B
0 0 1 0 DAC C
0 0 1 1 DAC D
0 1 0 0 DAC E
0 1 0 1 DAC F
0 1 1 0 DAC G
0 1 1 1 DAC H
1 1 1 1 All DACs
* Address codes not shown are reserved and should not be used.