+2.7V, Low-Power, Multichannel,

Serial 8-Bit ADCs

______________________________________________________________________________________

11

in control bytes of $FF (hex), which trigger single-

ended, unipolar conversions on CH7 (MAX1110) or

CH3 (MAX1111) in external clock mode without power-

ing down between conversions. In external clock mode,

the SSTRB output pulses high for two clock periods

before the most significant bit of the 8-bit conversion

result is shifted out of DOUT. Varying the analog input

alters the output code. A total of 10 clock cycles is

required per conversion. All transitions of the SSTRB

and DOUT outputs occur on SCLK’s falling edge.

How to Start a Conversion

A conversion is started by clocking a control byte into

DIN. With CS low, each rising edge on SCLK clocks a bit

from DIN into the MAX1110/MAX1111’s internal shift reg-

ister. After CS falls, the first arriving logic “1” bit at DIN

defines the MSB of the control byte. Until this first start bit

arrives, any number of logic “0” bits can be clocked into

DIN with no effect. Table 3 shows the control-byte format.

The MAX1110/MAX1111 are compatible with MICROWIRE,

SPI, and QSPI devices. For SPI, select the correct clock

polarity and sampling edge in the SPI control registers:

set CPOL = 0 and CPHA = 0. MICROWIRE, SPI, and

QSPI all transmit a byte and receive a byte at the same

time. Using the Typical Operating Circuit (Figure 3), the

simplest software interface requires three 8-bit transfers

to perform a conversion (one 8-bit transfer to configure

the ADC, and two more 8-bit transfers to clock out the

8-bit conversion result). Figure 6 shows the MAX1110/

MAX1111 common serial-interface connections.

1µF

0.1µF

DGND

AGND

CS

SCLK

DIN

DOUT

SSTRB

SHDN

+3V

N.C.

0.01µF

CH7 (CH3)

COM

REFOUT

REFIN

C1

1µF

0V TO

+2.048V

ANALOG

INPUT

OSCILLOSCOPE

CH1

CH2

CH3

CH4

*FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FF (HEX)

( ) ARE FOR THE MAX1111.

MAX1110

MAX1111

+3V

500kHz

OSCILLATOR

SCLK

SSTRB

DOUT*

Figure 5. Quick-Look Circuit

Table 4. Full-Scale and Zero-Scale Voltages

UNIPOLAR MODE

+ COM

Full Scale

COM

COM

+ COM

Positive

Full Scale

Zero Scale

Zero

Scale

BIPOLAR MODE

Negative

Full Scale