MAX5188_01 Datasheet, PDF (8/14 Pages) Maxim Integrated Products – Dual, 8-Bit, 40MHz, Current/Voltage, Alternate-Phase Output DACs

Dual, 8-Bit, 40MHz, Current/Voltage,
Alternate-Phase Output DACs
REN
1 2V REF
REFO
REFR
AV_DD
AGND
CS
DACEN
PD
CURRENT-
SOURCE ARRAY
CREF1
CREF2
9.6k*
CLK
DAC 1 SWITCHES
DAC 2 SWITCHES
OUTPUT
LATCHES
OUTPUT
LATCHES
MSB DECODE
MSB DECODE
INPUT
LATCHES
INPUT
LATCHES
OUT1P
OUT1N
OUT2P
OUT2N
MAX5188
MAX5191
DV_DD DGND
*INTERNAL 400Ω AND 9.6kΩ RESISTORS FOR MAX5191 ONLY.
Figure 1. Functional Diagram
D7–D0
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
400Ω 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, 400Ω load resis-
tors. Using the internal +1.2V reference voltage, the inte-
grated reference output current resistor of the MAX5191
(R_SET = 9.6kΩ) sets I_REF to 125µA and I_FS to 1mA.
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