SET/RESET Functions

The MAX4820/MAX4821 feature set and reset inputs that

allow the user to simultaneously turn all outputs on or off

using a single control line. Drive SET low to set all latch-

es and registers to 1 and turn all outputs on. SET over-

rides all serial/parallel control inputs. Drive RESET low to

clear all latches and registers and turn all outputs off.

RESET overrides all other inputs, including SET.

Applications Information

Daisy Chaining

The MAX4820 features a digital output, DOUT, that pro-

vides a simple way to daisy chain multiple devices. This

feature allows the user to drive large banks of relays

using only a single serial interface. To daisy chain multi-

ple devices, connect all CS pins together, and connect

the DOUT of one device to the DIN of another device

(see Figure 3). During operation, a stream of serial data

is shifted through all the MAX4820s in series. When CS

goes high, all outputs update simultaneously.

The MAX4820 can also be used in a slave configuration

that allows the user to address individual devices.

Connect all the DIN pins together, and use the CS input

to address one device at a time. Drive CS low to select

a slave and input the data into the shift register. Drive

CS high to latch the data and turn on the appropriate

outputs. Typically, in this configuration only one slave is

addressed at a time.

+3.3V/+5V, 8-Channel, Cascadable Relay Drivers

with Serial/Parallel Interface

8

_______________________________________________________________________________________

CS

A_

LVL

Figure 2. Parallel Interface Timing Diagram (MAX4821 only)

MAX4820

DIN

DIN

SCLK

SCLK

CS

SCLK

DOUT

OUT8

PGND

CS

0.1

µF

GND

OUT1

MAX4820

DIN

SCLK

DOUT

OUT8

PGND

CS

0.1

µF

GND

OUT1

MAX4820

DIN

SCLK

DOUT

OUT8

PGND

CS

0.1

µF

GND

OUT1

SCLK

Figure 3. Daisy-Chain Configuration

Table 2. Parallel Interface Address Map

(MAX4821 Only)

A2

A1

A0

OUTPUT

Low

Low

Low

OUT1

Low

Low

High

OUT2

Low

High

Low

OUT3

Low

High

High

OUT4

High

Low

Low

OUT5

High

Low

High

OUT6

High

High

Low

OUT7

High

High

High

OUT8