+3V, Quad, 10-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________

9

In shutdown mode, the MAX5251 output amplifiers and

the reference inputs enter a high-impedance state. The

serial interface remains active. Data in the input regis-

ters is retained in shutdown, allowing the MAX5251 to

recall the output states prior to entering shutdown. Exit

shutdown mode either by recalling the previous config-

uration or by updating the DACs with new data. When

powering up the device or bringing it out of shutdown,

allow 20µs for the outputs to stabilize.

Serial-Interface Configurations

The MAX5251’s 3-wire serial interface is compatible

with both Microwire™ (Figure 2) and SPI™/QSPI™

(Figure 3). The serial input word consists of two address

bits and two control bits followed by 10+2 data bits

(MSB first), as shown in Figure 4. The 4-bit address/

control code determines the MAX5251’s response out-

lined in Table 1. The connection between DOUT and

the serial-interface port is not necessary, but may be

used for data echo. Data held in the MAX5251’s shift

register can be shifted out of DOUT and returned to the

microprocessor (µP) for data verification.

The MAX5251’s digital inputs are double buffered.

Depending on the command issued through the serial

interface, the input register(s) can be loaded without

affecting the DAC register(s), the DAC register(s) can

be loaded directly, or all four DAC registers can be

updated simultaneously from the input registers

(Table 1).

Serial-Interface Description

The MAX5251 requires 16 bits of serial data. Table 1

lists the serial-interface programming commands. For

certain commands, the 10+2 data bits are “don’t

cares.” Data is sent MSB first and can be sent in two

8-bit packets or one 16-bit word (

CS must remain low

until 16 bits are transferred). The serial data is com-

posed of two DAC address bits (A1, A0) and two con-

trol bits (C1, C0), followed by the 10+2 data bits

D9…D0, S1, S0 (Figure 4). Set both sub-bits (S0, S1) to

zero. The 4-bit address/control code determines:

• The register(s) to be updated

• The clock edge on which data is to be clocked out

via the serial-data output (DOUT)

• The state of the user-programmable logic output

(UPO)

• If the part is to go into shutdown mode (assuming

PDL is high)

• How the part is configured when exiting shutdown

mode.

SCLK

DIN

DOUT*

CS

SK

SO

SI*

I/O

MAX5251

MICROWIRE

PORT

*THE DOUT-SI CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX5251,

BUT MAY BE USED FOR READBACK PURPOSES.

Figure 2. Connections for Microwire

DOUT*

DIN

SCLK

CS

MISO*

MOSI

SCK

I/O

SPI/QSPI

PORT

SS

+3.3V

CPOL = 0,CPHA = 0

*THE DOUT-MISO CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX5251,

BUT MAY BE USED FOR READBACK PURPOSES.

MAX5251

Figure 3. Connections for SPI/QSPI

Figure 4. Serial-Data Format

MSB ..................................................................................LSB

16 Bits of Serial Data

Address

Bits

Control

Bits

Data Bits

MSB.................................LSB

A1

A0

C1

C0

D9 ...................................D0 S1 S0

10+2 Data Bits

4 Address/

Control Bits