Detailed Description

The MAX5821 is a dual, 10-bit, voltage-output DAC with

consists of a serial interface, power-down circuitry, dual

input and DAC registers, two 10-bit resistor string

DACs, two unity-gain output buffers, and output resistor

networks. The serial interface decodes the address and

control bits, routing the data to the proper input or DAC

register. Data can be directly written to the DAC regis-

ter, immediately updating the device output, or can be

written to the input register without changing the DAC

output. Both registers retain data as long as the device

is powered.

DAC Operation

The MAX5821 uses a segmented resistor string DAC

architecture, which saves power in the overall system

and guarantees output monotonicity. The MAX5821’s

input coding is straight binary, with the output voltage

given by the following equation:

where N = 10 (bits), and D = the decimal value of the

input code (0 to 1023).

Output Buffer

The MAX5821 analog outputs are buffered by preci-

sion, unity-gain followers that slew 0.5V/µs. Each buffer

output swings rail-to-rail, and is capable of driving 5k

Ω

in parallel with 200pF. The output settles to ±0.5LSB

within 4µs.

Power-On Reset

The MAX5821 features an internal POR circuit that ini-

tializes the device upon power-up. The DAC registers

are set to zero scale and the device is powered down,

with the output buffers disabled and the outputs pulled

to GND through the 100k

Ω termination resistor.

Following power-up, a wake-up command must be initi-

ated before any conversions are performed.

Power-Down Modes

The MAX5821 has three software-controlled low-power

power-down modes. All three modes disable the output

buffers and disconnect the DAC resistor strings from

REF, reducing supply current draw to 1µA and the ref-

erence current draw to less than 1µA. In power-down

mode 0, the device output is high impedance. In

power-down mode 1, the device output is internally

pulled to GND by a 1k

Ω termination resistor. In power-

down mode 2, the device output is internally pulled to

GND by a 100k

Ω termination resistor. Table 1 shows

the power-down mode command words.

Upon wake-up, the DAC output is restored to its previ-

ous value. Data is retained in the input and DAC regis-

ters during power-down mode.

Digital Interface

wire interface consisting of a serial data line (SDA) and

a serial clock line (SCL). The MAX5821 is SMBus com-

SCL facilitate bidirectional communication between the

MAX5821 and the master at rates up to 400kHz. Figure

1 shows the 2-wire interface timing diagram. The

MAX5821 is a transmit/receive slave-only device, rely-

ing upon a master to generate a clock signal. The mas-

ter (typically a microcontroller) initiates data transfer on

the bus and generates SCL to permit that transfer.

A master device communicates to the MAX5821 by

transmitting the proper address followed by command

and/or data words. Each transmit sequence is framed

a STOP (P) condition. Each word transmitted over the

V

VD

OUT

REF

N

_

()

=

×

2

Dual, 10-Bit, Low-Power, 2-Wire, Serial

Voltage-Output DAC

_______________________________________________________________________________________

7

Pin Description

PIN

NAME

FUNCTION

Power Supply

2

GND

Ground

3

ADD

Address Select. A logic high sets the address LSB to 1; a logic low sets the address LSB to zero.

4

SCL

Serial Clock Input

5

SDA

Bidirectional Serial Data Interface

6

REF

Reference Input

7

OUTA

DAC A Output

8

OUTB

DAC B Output