Rainbow Electronics MAX5191 - Manual (Page 8)

MAX5188/MAX5191
Dual, 8-Bit, 40MHz, Current/Voltage,
Alternate-Phase Output DACs
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Detailed Description
The MAX5188/MAX5191 are dual 8-bit digital-to-analog
converters (DACs) capable of operating with clock
speeds up to 40MHz. Each of these dual converters
consists of separate input and DAC registers, followed
by a current-source array capable of generating up to
1.5mA full-scale output current (Figure 1). An integrat-
ed +1.2V voltage reference and control amplifier deter-
mine the data converters’ full-scale output currents/
voltages. Careful reference design ensures close gain
matching and excellent drift characteristics. The
MAX5191’s voltage output operation features matched
400
Ω on-chip resistors that convert the current from the
current array into a voltage.
Internal Reference
and Control Amplifier
The MAX5188/MAX5191 provide an integrated
50ppm/°C, +1.2V, low-noise bandgap reference that
can be disabled and overridden by an external refer-
ence voltage. REFO serves either as an input for an
external reference or as an output for the integrated ref-
erence. If REN is connected to DGND, the internal ref-
erence is selected and REFO provides a +1.2V output.
Due to its limited 10µA output drive capability, the
REFO pin must be buffered with an external amplifier if
heavier loading is required.
The MAX5188/MAX5191 also employ a control amplifi-
er, designed to simultaneously regulate the full-scale
output current I
FS for both MAX5188/MAX5191 outputs.
The output current is calculated as follows:
I FS = 8 ✕ I REF
where I REF is the reference output current (I REF =
V REFO / R SET ) and I FS is the full-scale output current.
R SET is the reference resistor that determines the
amplifier’s output current (Figure 2) on the MAX5188.
This current is mirrored into the current-source array,
where it is equally distributed between matched current
segments and summed to valid output current readings
for the DACs.
Inside the MAX5191, each output current (DAC1 and
DAC2) is converted to an output voltage (V
OUT1 , V OUT2 )
with two internal, ground-referenced, 400
Ω load resis-
tors. Using the internal +1.2V reference voltage, the inte-
grated reference output current resistor of the MAX5191
(R
SET = 9.6k
Ω) sets I
REF to 125µA and I FS to 1mA.
9.6k*
REFR
REFO
1.2V REF
REN
CURRENT-
SOURCE ARRAY
DAC 1 SWITCHES
DAC 2 SWITCHES
400
Ω
*
MSB DECODE
CLK
OUTPUT
LATCHES
OUTPUT
LATCHES
MSB DECODE
INPUT
LATCHES
*INTERNAL 400 Ω AND 9.6kΩ RESISTORS FOR MAX5191 ONLY.
INPUT
LATCHES
AV DD AGND CS DACEN PD
DV DD DGND
D7–D0
CREF2
MAX5188
MAX5191
CREF1
OUT2P
OUT1P
OUT2N
OUT1N
400
Ω
*
400
Ω
*
400
Ω
*
Figure 1. Functional Diagram