+2.5V to +5.5V, Low-Power, Single/Dual,

8-Bit Voltage-Output DACs in µMAX Package

______________________________________________________________________________________

13

Table 6. Analog Output vs. Code

Microprocessor Interfacing

The MAX548A/MAX549A/MAX550A serial interface is

SPI/QSPI and Microwire compatible. For SPI/QSPI, clear

the CPOL and CPHA bits (CPOL = 0 and CPHA = 0).

CPOL = 0 sets the clock idle state to zero, and CPHA =

0 changes data at SCLK’s falling edge. This is the

Microwire default condition. If a serial port is not avail-

able on your microprocessor, three bits of a parallel port

can be used to emulate a serial port by bit manipulation.

Operate the serial clock only when necessary, to mini-

mize digital feedthrough at the DAC registers.

__________Applications Information

Power-Supply

and Ground Considerations

Connect GND to the highest quality ground available.

The reference input can be used without bypassing.

However, for optimum line/load-transient response and

noise performance, bypass the reference input with a

0.1µF to 4.7µF capacitor to GND.

Careful PC board layout minimizes crosstalk in DAC regis-

ters, the reference, and the digital inputs. Separate analog

traces by running ground traces between them. Make sure

that high-frequency digital lines are not routed parallel to

analog lines.

AC Considerations

Digital Feedthrough

High-speed data at any of the digital input pins can

couple through a DAC’s internal stray package capaci-

tance and cause noise (digital feedthrough) at the DAC

output, even though LDAC and/or CS are held high

(see

Typical Operating Characteristics). Test digital

feedthrough by holding LDAC and/or CS high and tog-

gling the digital inputs from all 1s to all 0s.

Analog Feedthrough

Due to internal stray capacitance, higher frequency analog

input signals at REF can couple to the output, even when

the input digital code is all 0s. This condition is shown in

the MAX549A/MAX550A Reference AC Feedthrough vs.

Frequency graph in the

Typical Operating Characteristics.

Test analog feedthrough by setting all DAC outputs to 0V

and sweeping REF.

_____________________________________________Pin Configurations (continued)

OUTB

SCLK

DIN

1

2

8

7

REF

OUTA

CS

GND

DIP/

µMAX

TOP VIEW

3

4

6

5

MAX549A

LDAC

SCLK

DIN

1

2

8

7

REF

OUT

CS

GND

DIP/

µMAX

3

4

6

5

MAX550A

ANALOG OUTPUT (V)

0

0

0

0

1

0

0

1

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

D6

1

1

D4

1

D5

1

0

D2

1

0

DAC CONTENTS

D0

1

0

D1

1

0

D3

1

0

D7

1

0

0

0

0

0

0

0

0

1

0

0

0