Datasheet

LTC2632
17
2632fa
OPERATION
The LTC2632 is a family of dual voltage output DACs in an
8-lead TSOT package. Each DAC can operate rail-to-rail
using an external reference, or with its full-scale voltage
set by an integrated reference. Fifteen 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 LTC2632 is controlled using
a 3-wire SPI/MICROWIRE compatible interface.
Power-On Reset
The LTC2632-HZ/LTC2632-LZ clear the output to zero-scale
when power is first applied, making system initialization
consistent 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 LTC2632 con-
tains circuitry to reduce the power-on glitch: the analog
output typically rises less than 10mV 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 LTC2632-HI/LTC2632-LI/LTC2632-LX provides an
alternative reset, setting the output to mid-scale when
power is first applied. The LTC2632-LI and LTC2632-HI
power-up in internal reference mode, with the output set
to a mid-scale voltage of 1.25V and 2.048V respectively.
The LTC2632-LX powers up in external reference mode,
with the output set to mid-scale of the external reference.
Default reference mode selection is described in the Refer-
ence Modes section.
Power Supply Sequencing
The voltage at REF (Pin 3) must be kept within the range
–0.3V ≤ V
REF
≤ V
CC
+ 0.3V (see the Absolute Maximum
Ratings section). 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 (LTC2632-
LI/LTC2632-LX/LTC2632-LZ) or 4.096V (LTC2632-HI/
LTC2632-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 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
1 1 1 1 All DACs
* Address codes not shown are reserved and should not be used.