Detailed description, Pin description – Rainbow Electronics MAX5842 User Manual
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MAX5842
Quad, 12-Bit, Low-Power, 2-Wire, Serial
Voltage-Output DAC
8
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Detailed Description
The MAX5842 is a quad, 12-bit, voltage-output DAC
with an I
2
C/SMBus-compatible 2-wire interface. The
device consists of a serial interface, power-down cir-
cuitry, four input and DAC registers, four 12-bit resistor
string DACs, four 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 register, immediately updating the device out-
put, 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 MAX5842 uses a segmented resistor string DAC
architecture, which saves power in the overall system
and guarantees output monotonicity. The MAX5842’s
input coding is straight binary, with the output voltage
given by the following equation:
where N = 12 (bits), and D = the decimal value of the
input code (0 to 4095).
Output Buffer
The MAX5842 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 MAX5842 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 MAX5842 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 reference current draw to less than 1µA. In
power-down mode 0, the device output is high imped-
ance. 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
The MAX5842 features an I
2
C/SMBus-compatible
2-wire interface consisting of a serial data line (SDA)
and a serial clock line (SCL). The MAX5842 is SMBus
compatible within the range of V
DD
= 2.7V to 3.6V. SDA
and SCL facilitate bidirectional communication between
the MAX5842 and the master at rates up to 400kHz.
Figure 1 shows the 2-wire interface timing diagram. The
MAX5842 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 MAX5842 by
transmitting the proper address followed by command
and/or data words. Each transmit sequence is framed
V
V
D
OUT
REF
N
_
( )
=
×
2
Pin Description
PIN
NAME
FUNCTION
1
ADD
Address Select. A logic high sets the address LSB to 1; a logic low sets the address LSB to zero.
2
SCL
Serial Clock Input
3
V
DD
Power Supply
4
GND
Ground
5
SDA
Bidirectional Serial Data Interface
6
REF
Reference Input
7
OUTA
DAC A Output
8
OUTB
DAC B Output
9
OUTC
DAC C Output
10
OUTD
DAC D Output