Datasheet

THEORY OF OPERATION
GENERAL DESCRIPTION
DIGITAL-TO-ANALOG SECTIONS
R R
12-BitR-2RLadder FourMSBsDecodedinto
15EqualSegments
2R2R 2R 2R
S0 S1 S11
2R
V
OUT
E15
2R
E2
2R
E1
V
REFH
-F
V
REFH
-S
V
REFL
-F
V
REFL
-S
OUTPUT RANGE
V
OUT
+
V
REFH
* V
REFL
65536
Code ) V
REFL
(1)
DAC8871
SBAS396A – JUNE 2007 – REVISED JUNE 2008 ............................................................................................................................................................. www.ti.com
The DAC8871 is a 16-bit, single-channel, serial-input, voltage-output DAC. It operates from a dual power supply
ranging from ± 13.5V to ± 19.8V, and typically consumes 10 µ A. The output range is from V
REFL
to V
REFH
. Data are
written to this device in a 16-bit word format, via an SPI serial interface. To ensure a known power-up state, the
DAC8871 is designed with a power-on reset function. After power on, the state of the RSTSEL pin sets the value
of the input register and DAC latch, which sets the output state of the V
OUT
pin. Refer to the Power-On Reset and
Hardware Reset section for more details.
Kelvin sense connections for the reference and analog ground are also included.
The DAC architecture consists of two matched DAC sections and is segmented. A simplified circuit diagram is
shown in Figure 38 . The four MSBs of the 16-bit data word are decoded to drive 15 switches, E1 to E15. Each of
these switches connects one of 15 matched resistors to either V
REFH
or V
REFL
. The remaining 12 bits of the data
word drive switches S0 to S11 of a 12-bit voltage mode R-2R ladder network.
Figure 38. DAC Architecture
The output of the DAC is:
Where Code is the decimal data word loaded to the DAC latch.
For example, if V
REFH
is +10V, and V
REFL
is – 10V, the range of V
OUT
is from – 10V (Code = 0000h) to +10V (Code
= FFFFh).
The range of V
REFL
is from – 18V to (V
REFH
– 1.25V), and the range of V
REFH
is 0V to +18V. The output from the
DAC8871 can be unipolar (from 0V to +18V) or bipolar by setting the proper V
REFL
and V
REFH
values.
14 Submit Documentation Feedback Copyright © 2007 – 2008, Texas Instruments Incorporated
Product Folder Link(s): DAC8871