Datasheet
MAX5115/MAX5116
Nonvolatile, Quad, 8-Bit DACs with 2-Wire Serial
Interface
______________________________________________________________________________________ 11
Detailed Description
The MAX5115/MAX5116 8-bit DACs feature internal,
nonvolatile registers that store the DAC states for initial-
ization during power-up. These devices consist of resis-
tor-string DACs, rail-to-rail output buffers, a shift
register, power-on reset (POR) circuitry, and volatile
and nonvolatile memory registers (Figures 1 and 2).
The shift register decodes the control and address bits,
routing the data to the proper registers. Writing data to
a selected volatile register immediately updates the
DAC outputs.
The volatile registers retain data as long as the device
is powered. Removing power clears the volatile regis-
ters. The nonvolatile registers retain data even after
power is removed. On startup, when power is first
applied, data from the nonvolatile registers is trans-
ferred to the volatile registers to automatically initialize
the device. Read data from the nonvolatile or volatile
registers using the 2-wire serial interface.
DAC Operation
The MAX5115/MAX5116 use a DAC matrix decoding
architecture that saves power. A resistor string divides
the difference between the external reference voltages,
V
REFH_
and V
REFL_
. Row and column decoders select
the appropriate tap from the resistor string, providing
the equivalent analog voltage. The resistor string pre-
sents a code-independent input impedance to the ref-
erence and guarantees a monotonic output. Figure 3
shows a simplified diagram of one DAC.
Output Buffer Amplifiers
The MAX5115/MAX5116 analog outputs are internally
buffered by a precision unity-gain amplifier. The outputs
swing from GND to V
DD
with a V
REFL_
-to-V
REFH_
output
transition. The amplifier outputs typically settle to ±0.5 LSB
in 8µs when loaded with 5kΩ in parallel with 100pF.
DAC Registers
The MAX5115/MAX5116 feature two registers per DAC,
a volatile and a nonvolatile register, that store the DAC
data. The volatile DAC register holds the current value
of each DAC. Write data to the volatile registers directly
from the 2-wire serial interface or by loading the previ-
ously stored data from the respective nonvolatile regis-
ter. Clear the volatile registers by removing power to
the device. The volatile registers are read/write.
The nonvolatile register retains the DAC values even
after power is removed. Read stored data using the 2-
wire serial interface. On power-up, the devices auto-
matically initialize with data stored in the nonvolatile
registers. The nonvolatile registers are read/write and
programmed to all zeros at the factory.
REFH_
REFL_
R1
R15
R16
R255
R0
D7
D6
D5
D4
DAC
MSB DECODER
D3
D0
D2 D1
LSB DECODER
Figure 3. DAC Simplified Circuit Diagram