In power-down mode, the MAX525 output amplifiers

and the reference inputs enter a high-impedance state.

The serial interface remains active. Data in the input

registers is retained in power-down, allowing the

MAX525 to recall the output states prior to entering

shutdown. Start up from power-down either by recalling

the previous configuration or by updating the DACs

with new data. When powering up the device or bring-

ing it out of shutdown, allow 15µs for the outputs to sta-

bilize.

Serial-Interface Configurations

The MAX525’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 12 data bits

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

control code determines the MAX525’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 MAX525’s shift

register can be shifted out of DOUT and returned to the

microprocessor (µP) for data verification.

The MAX525’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 MAX525 requires 16 bits of serial data. Table 1 lists

the serial-interface programming commands. For cer-

tain commands, the 12 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 composed of two DAC

address bits (A1, A0) and two control bits (C1, C0),

followed by the 12 data bits D11…D0 (Figure 4). 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 coming out of shut-

down mode.

Low-Power, Quad, 12-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________

9

SCLK

DIN

DOUT*

CS

SK

SO

SI*

I/O

MAX525

MICROWIRE

PORT

*THE DOUT-SI CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX525,

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

+5V

CPOL = 0, CPHA = 0

*THE DOUT-MISO CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX525,

BUT MAY BE USED FOR READBACK PURPOSES.

MAX525

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

D11................................................D0

12 Data Bits

4 Address/

Control Bits