Nonvolatile, Quad, 8-Bit DACs with 2-Wire Serial

Interface

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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,

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

transition. The amplifier outputs typically settle to ±0.5 LSB

in 8µs when loaded with 5k

Ω 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

D3

D0

D2

D1

LSB DECODER

Figure 3. DAC Simplified Circuit Diagram