LTC2634-HMI10 LINER [Linear Technology], LTC2634-HMI10 Datasheet - Page 19

• Manufacturer Part Number: LTC2634-HMI10
• Manufacturer: LINER [Linear Technology]

OPERATION
The LTC2634 is a family of quad voltage output DACs in
16-lead QFN and 10-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 LTC2634
is controlled using a 3-wire SPI/MICROWIRE compatible
interface.
Power-On Reset
The LTC2634-HZ/LTC2634-LZ clear the output to zero-scale
when power is fi rst 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 LTC2634
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 LTC2634-HMI/LTC2634-HMX/LTC2634-LMI/
LTC2634-LMX provide an alternative reset, setting the
output to mid-scale when power is fi rst applied. The
LTC2634-LMI and LTC2634-HMI power up in internal
reference mode, with the output set to a mid-scale volt-
age of 1.25V and 2.048V, respectively. The LTC2634-LMX
and LTC2634-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 Refer-
ence Modes section.
Power Supply Sequencing
The voltage at REF (Pin 10, QFN/Pin 7, MSOP) must be
kept within the range –0.3V ≤ V
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
transition.
Transfer Function
The digital-to-analog transfer function is:
where k is the decimal equivalent of the binary DAC
input code, N is the resolution, and V
(LTC2634-LMI/LTC2634-LMX/LTC2634-LZ) or 4.096V
(LTC2634-HMI/LTC2634-HMX/LTC2634-HZ) when in
internal reference mode, and the voltage at REF when in
external reference mode. The resulting DAC output span
is 0V to V
Serial Interface
The CS/LD input is level-triggered. When this input is
taken low, it acts as a chip-select signal, enabling the SDI
and SCK buffers and the input shift register. Data (SDI
input) is transferred at the next 24 rising SCK edges.
The 4-bit command, C3-C0, is loaded fi rst; then the 4-bit
DAC address, A3-A0; and fi nally the 16-bit data word.
The data word comprises the 12-, 10- or 8-bit input code,
ordered MSB to LSB, followed by 4, 6 or 8 don’t-care
bits (LTC2634-12/LTC2634-10/LTC2634-8 respectively;
see Figure 2). Data can only be transferred to the device
when the CS/LD signal is low, beginning on the fi rst rising
edge of SCK. SCK may be high or low at the falling edge
V
OUT IDEAL
(
REF
, as it is necessary to tie REFLO to GND.
)
=
⎛
⎝ ⎜
2
k
N
⎞
⎠ ⎟
(
V
REF
–
V
REFLO
REF
≤ V
)
REF
LTC2634
+
CC
V
REFLO
is either 2.5V
+ 0.3V (see
19
CC
is in
2634fb