+3V/+5V, Low-Power, 8-Bit Octal DAC

with Rail-to-Rail Output Buffers

10

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Detailed Description

Serial Interface

At power-on, the serial interface and all DACs are

cleared and set to code zero. The serial data output

(DOUT) is set to transition on SCLK’s falling edge.

The MAX5258/MAX5259 communicate with micro-

processors (µPs) through a synchronous, 3-wire inter-

face (Figure 1). Data is sent MSB first and can be

transmitted in two 4-bit and one 8-bit (byte) packets, or

one 16-bit word. The first two bits are ignored. A 4-wire

interface adds a line for LDAC, allowing asynchronous

updating. Data is transmitted and received simultane-

ously.

Figure 2 shows the detailed serial-interface timing. Note

that the clock should be low if it is stopped between

updates. DOUT does not go into a high-impedance state

if the clock idles or CS is high.

Serial data is clocked into the data registers in MSB-first

format, with the address and configuration information

preceding the actual DAC data. Data is clocked in on

SCLK’s rising edge while CS is low. Data at DOUT is

clocked out 16 clock cycles later, either at SCLK’s falling

edge (default or mode 0) or rising edge (mode 1).

CS must be low to enable the device. If CS is high, the

interface is disabled and DOUT remains unchanged.

CS must go low at least 40ns before the first rising edge

of the clock pulse to properly clock in the first bit. With

CS low, data is clocked into the MAX5258/MAX5259’s

internal shift register on the rising edge of the external

serial clock. Always clock in the full 16 bits.

Serial Input Data Format and Control Codes

The 16-bit serial input format, shown in Figure 3, com-

prises two “don’t care” bits, three DAC address bits (A2,

A1, A0), three control bits (C2, C1, C0), and eight data

bits (D7…D0). The 6-bit address/control code configures

the DAC as shown in Table 1.

Pin Description

PIN

NAME

FUNCTION

1

OUTB

DAC B Voltage Output

2

OUTA

DAC A Voltage Output

3

GND

Ground

Power Supply

5

REF

Reference Voltage Input

6

LDAC

Load DAC Input. Driving this asynchronous input low transfers the contents of each input register

to its respective DAC registers.

7

OUTE

DAC E Voltage Output

8

OUTF

DAC F Voltage Output

9

OUTG

DAC G Voltage Output

10

OUTH

DAC H Voltage Output

11

CS

Chip Select Input. Data is shifted in and out when CS is low. Programming commands are executed

when CS returns high.

12

SCLK

Serial Clock Input. Data is clocked in on the rising edge and clocked out on the falling edge

(default) or rising edge (A2 = 1; see Table 1).

13

DIN

Serial Data Input. Data is clocked in on the rising edge of SCLK.

14

DOUT

Serial Data Output. Sinks and sources current. Data at DOUT can be clocked out on the falling

edge (mode 0) or rising edge (mode 1) of SCLK (Table 1).

15

OUTD

DAC D Voltage Output

16

OUTC

DAC C Voltage Output