MAX5187/MAX5190
8-Bit, 40MHz, Current/Voltage-Output DACs
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Detailed Description
The MAX5187/MAX5190 are 8-bit DACs capable of
operating with clock speeds up to 40MHz. Each con-
verter consists of separate input and DAC registers, fol-
lowed by a current-source array capable of generating
up to 1.5mA full-scale output current (Figure 1). An inte-
grated +1.2V voltage reference and control amplifier
determine the data converters’ full-scale output cur-
rents/voltages. Careful reference design ensures close
gain matching and excellent drift characteristics. The
MAX5190’s voltage-output operation features matched
400Ω on-chip resistors that convert the current array
current into a voltage.
Internal Reference
and Control Amplifier
The MAX5187/MAX5190 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 external refer-
ence input or an integrated reference output. If REN is
connected to DGND, the internal reference is selected
and REFO provides a +1.2V output. Due to its limited
10µA output drive capability, REFO must be buffered
with an external amplifier if heavier loading is required.
The MAX5187/MAX5190 also employ a control amplifi-
er, designed to simultaneously regulate the full-scale
output current (I
FS
) for both outputs of the devices. The
output current is calculated as follows:
I
FS
= 8 x 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 on the MAX5187 (Figure 2).
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.
The MAX5190 converts this output current into a differ-
ential output voltage (V
OUT
) with two internal, ground-
referenced 400Ω load resistors. Using the internal
+1.2V reference voltage, the MAX5190’s integrated
reference output current resistor (R
SET
= 9.6kΩ) sets
I
REF
to 125µA and I
FS
to 1mA.
RESISTORS FOR MAX5190 ONLY.
