Rainbow Electronics MAX5190 - Manual (Page 8)

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
400
Ω 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 400 Ω load resistors. Using the internal
+1.2V reference voltage, the MAX5190’s integrated
reference output current resistor (R
SET = 9.6k
Ω) sets
I REF to 125µA and I FS to 1mA.
REFR
REFO
1.2V REF
REN
CURRENT-
SOURCE ARRAY
DAC SWITCHES
400 Ω 400 Ω*
MSB DECODE
CLK
OUTPUT
LATCHES
OUTPUT
LATCHES
MSB DECODE
*INTERNAL 400 Ω AND 9.6kΩ
RESISTORS FOR MAX5190 ONLY.
AV DD AGND CS DACEN PD
*
DV DD DGND
D7–D0
MAX5187
MAX5190
CREF
OUTN
OUTP
INPUT
LATCHES
INPUT
LATCHES
9.6k*
Figure 1. Functional Diagram