input register, it transfers its contents to the DAC latch

on CS’s low-to-high transition (Figure 3). Note that if CS

is not kept low during the entire 16 SCLK cycles, data

will be corrupted. In this case, reload the DAC latch

with a new 16-bit word. The serial clock (SCLK) can

idle either high or low between transitions. Figure 4

shows the complete 3-wire serial interface transmis-

sion. Table 3 lists serial interface mapping.

Applications Information

Device Powered by an External Reference

Since the MAX5385 generates an output voltage pro-

accuracy of the on-board reference, thereby affecting

the overall accuracy of the DAC. The circuit in Figure 5

rejects this power-supply noise by powering the device

directly with a precision voltage reference, improving

overall system accuracy. The MAX6103 (+3V, 75ppm)

or the MAX6105 (+5V, 75ppm) precision voltage refer-

ences are ideal choices due to the low power require-

ments of the MAX5385. This solution is also useful

when the required full-scale output voltage is different

from the available supply voltages.

Digital Inputs and Interface Logic

The digital interface for the 8-bit DAC is based on a

3-wire standard that is compatible with SPI, QSPI, and

MICROWIRE interfaces. The three digital inputs (CS, DIN,

and SCLK) load the digital input serially into the DAC.

All the digital inputs include Schmitt-trigger buffers to

accept slow-transition interfaces. This means that opto-

couplers can interface directly to the MAX5383/

MAX5384/MAX5385 without additional external logic.

The digital inputs are compatible with CMOS logic levels

and can be driven with voltages up to +5.5V regardless

of the supply voltage.

Power-Supply Bypassing and Layout

Careful PC board layout is important for best system

performance. To reduce crosstalk and noise injection,

keep analog and digital signals separate. To ensure

that the ground return from GND to the supply ground

is short and low impedance, a ground plane is recom-

as close as possible to the device. If the supply is

excessively noisy, connect a 10

Ω resistor in series with

Low-Cost, Low-Power, 8-Bit DACs with 3-Wire

Serial Interface in SOT23

_______________________________________________________________________________________

9

Table 3. Serial Interface Mapping

X

= Don’t care

16-BIT SERIAL WORD

ANALOG

MSB

LSB

OUTPUT

FUNCTION

XX00

0000

0000

XXXX

0V

Normal operation

XX00

1111

1111

XXXX

× (255/256)

Normal operation

XX00

0000

0001

XXXX

× (1/256)

Normal operation

XX00

1000

0000

XXXX

× (128/256)

Normal operation

XX01

XXXX

XXXX

XXXX

0V

Shutdown,

1k

Ω to GND

XX10

XXXX

XXXX

XXXX

0V

Shutdown,

100k

Ω to GND

XX11

XXXX

XXXX

XXXX

0V

Shutdown,

1M

Ω to GND

Table 2. Shutdown Modes

DAC CODE

[D13 AND D12]

MODE

OUTPUT RESISTANCE TO

GROUND (

Ω)

MAXIMUM SUPPLY

CURRENT (

µA)

01

Shutdown

1k

1

10

Shutdown

100k

1

11

Shutdown

1M

1