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MAX110/MAX111

Low-Cost, 2-Channel, ±14-Bit Serial ADCs

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ADC Operation

The output data from the MAX110/MAX111 is arranged

in twos-complement format (Figures 4, 5). The sign bit

(POL) is shifted out first, followed by the overrange bit

(OR), and the 14 data bits (MSB first) (see Figure 6).

The MAX110 operates from ±5V power supplies and

converts low-frequency analog signals in the ±3V

range when using the maximum reference voltage of

REF

= 3V (V

REF

= V

REF+

- V

REF-

). Within the ±3V input

range, greater accuracy is obtained within ±2.5V (see

Electrical Characteristics

for details). Note that a nega-

tive input voltage is defined as V

IN-

> V

IN+

. For the

MAX110, the absolute voltage at any analog input pin

must remain within the (V

+ 2.25V) to (V

- 2.25V)

range.

The MAX111 operates from a single +5V supply and

converts low-frequency differential analog signals in the

±1.5V range when using the maximum reference volt-

age of V

REF

= 1.5V. As indicated in the

Electrical

Characteristics

, greater accuracy is achieved within the

±1.2V range. The absolute voltage at any analog input

pin for the MAX111 must remain within 0V to V

- 3.2V.

When V

IN-

> V

IN+

the input is interpreted as negative.

The overrange bit (OFL) is provided to sense when the

input voltage level has exceeded the reference voltage

level. The converter does not “saturate” until the input

voltage is typically 20% larger. The linearity is not guar-

anteed in this range. Note that the overrange bit works

properly if the reference voltage remains within the rec-

ommended voltage range (see

Reference Inputs

). If the

reference voltage exceeds the recommended input

range, the overrange bit may not operate properly.

Digital Interface—Starting a Conversion

Data is transferred into and out of the serial I/O shift

at SCLK. This fully static shift register allows SCLK to

range from DC to 2MHz. Output data from the ADC is

clocked out on SCLK’s falling edge and should be read

on SCLK’s rising edge. Input data to the ADC at DIN is

clocked in on SCLK’s rising edge. A new conversion

begins when CS returns high, provided the MSB in the

input control word (NO-OP) is a 1 (see

Using the

MAX110/MAX111 with MICROWIRE, SPI, and QSPI

Serial Interfaces

). Figure 6 shows the detailed serial-

interface timing diagram.

CCSS

must remain high during the conversion (while

BUSY remains low). Bringing CS low during the conver-

sion causes the ADC to stop converting, and may

result in erroneous output data.

Using the MAX110/MAX111 with SPI, QSPI, and

MICROWIRE Serial Interfaces

Figure 7 shows the most common serial-interface con-

nections. The MAX110/MAX111 are compatible with

SPI, QSPI (CPHA = 0, CPOL = 0), and MICROWIRE

serial-interface standards.

XCLK

TTL/CMOS

RCSEL

GND

+5V

-5V (0V)

( ) ARE FOR MAX111.

(AGND)

MAX110

MAX111

Figure 3b. Connection for Internal RC-Oscillator Mode—XCLK

connects to the internal RC oscillator. Note, the pull-up resistor

is not necessary if the internal oscillator is never shut down.