Rainbow Electronics MAX5811 - Manual (Page 7)

MAX5811
10-Bit Low Power 2-Wire Interface Serial,
Voltage-Output DAC
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Detailed Description
The MAX5811 is a 10-bit, voltage-output DAC with an
I
2 C/SMBus-compatible 2-wire interface. The device
consists of a serial interface, power-down circuitry,
input and DAC registers, a 10-bit resistor string DAC,
unity-gain output buffer, and output resistor network.
The serial interface decodes the address and control
bits, routing the data to either the input or DAC register.
Data can be directly written to the DAC register imme-
diately 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 pow-
ered.
DAC Operation
The MAX5811 uses a segmented resistor string DAC
architecture, which saves power in the overall system
and guarantees output monotonicity. The MAX5811’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 MAX5811 analog output is buffered by a precision,
unity-gain follower that slews at about 0.5V/µs. The
buffer output swings rail-to-rail, and is capable of dri-
ving 5k
Ω in parallel with 200pF. The output settles to
±0.5LSB within 4µs.
Power-On Reset
The MAX5811 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 buffer disabled and the output pulled to
GND through the 100k
Ω termination resistor. Following
power-up, a wake-up command must be initiated
before any conversions are performed.
Power-Down Modes
The MAX5811 has three software-controlled low-power
power-down modes. All three modes disable the output
buffer and disconnect the DAC resistor string from V
DD ,
reducing supply current draw to 300nA. 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
The MAX5811 features an I 2 C/SMBus-compatible 2-
wire interface consisting of a serial data line (SDA) and
V
V D
OUT
REF
N
=
× ( )
2
Pin Description
PIN NAME FUNCTION
1 V DD Power Supply and DAC Reference Input
2 GND Ground
3 SDA Bidirectional Serial Data I/O
4 SCL Serial Clock Line
5 ADD Address Select. A logic high sets the address LSB to 1, a logic low sets the address LSB to 0.
6 OUT Analog Output
Table 1. Power-Down Command Bits
POWER-DOWN
COMMAND BITS
PD1 PD0
MODE/FUNCTION
0 0 Power-up device. DAC output restored to previous value.
0 1 Power-down mode 0. Power-down device with output floating.
1 0 Power-down mode 1. Power-down device with output terminated with 1k Ω to GND.
1 1 Power-down mode 2. Power-down device with output terminated with 100k Ω to GND.