Dual, 8-Bit, 40MHz, Current/Voltage,

Alternate-Phase Output DACs

8

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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

The output current is calculated as follows:

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

Ω load

resistors. Using the internal +1.2V reference voltage,

the integrated reference output current resistor of the

1mA.

9.6k*

REFR

REFO

1.2V REF

REN

CURRENT-

SOURCE ARRAY

DAC 1 SWITCHES

DAC 2 SWITCHES

MSB DECODE

CLK

OUTPUT

LATCHES

OUTPUT

LATCHES

MSB DECODE

INPUT

LATCHES

*INTERNAL 400

Ω AND 9.6kΩ RESISTORS FOR MAX5191 ONLY.

INPUT

LATCHES

AGND

CS

DACEN

PD

DGND

D7–D0

CREF2

MAX5188

MAX5191

CREF1

OUT2P

OUT1P

OUT2N

OUT1N

Figure 1. Functional Diagram