Rainbow Electronics MAX5123 - Manual (Page 10)

MAX5122/MAX5123
+5V/+3V, 12-Bit, Serial, Force/Sense DACs
with 10ppm/°C Internal Reference
10 ______________________________________________________________________________________
_______________Detailed Description
The MAX5122/MAX5123 12-bit, force/sense DACs are
easily configured with a 3-wire serial interface. They
include a 16-bit data-in/data-out shift register and have
a double-buffered digital input consisting of an input
register and a DAC register. In addition, these devices
employ precision bandgap references, as well as an
output amplifier with accessible feedback and output
pins that can be used to set the gain externally (Figure
1) or for forcing and sensing applications. These DACs
are designed with an inverted R-2R ladder network
(Figure 2) that produces a weighted voltage proportion-
al to the digital input code.
Internal Reference
Both devices use an on-board precision bandgap ref-
erence with a low temperature coefficient of only
10ppm/°C (max) to generate an output voltage of +2.5V
(MAX5122) or +1.25V (MAX5123). The REF pin can
source up to 100µA and may become unstable with
capacitive loads exceeding 100pF. REFADJ can be
used for minor adjustments to the reference voltage.
MAX5122
MAX5123
SR
CONTROL
16-BIT
SHIFT REGISTER
DECODE
CONTROL
INPUT
REGISTER
BANDGAP
REFERENCE
REFERENCE
BUFFER
DAC
REGISTER
DAC
2X
(X1)
DOUT
UPO
FB
OUT
4k
1.25V
12
AGND DGND V
DD
DIN SCLK CS
2.5V (1.25V)
LOGIC
OUTPUT
CLR
RSTVAL
PDL
PD
REFADJ REF
( ) ARE FOR MAX5123 ONLY.
Figure 1. Simplified Functional Diagram
OUT
FB
NOTE: SHOWN FOR ALL 1s ON DAC.
D0 D9 D10 D11
*INTERNAL REFERENCE: +2.5V (MAX5122),
+1.25V (MAX5123); OR EXTERNAL REFERENCE
2R 2R 2R 2R 2R
R R R
REF*
AGND
Figure 2. Simplified Inverted R-2R DAC Structure