MAX1221 datasheet(33/44 Pages) MAXIM

33 / 44 page

12-Bit, Multichannel ADCs/DACs with FIFO,

Temperature Sensing, and GPIO Ports

______________________________________________________________________________________

and forces them to a high-impedance state. DAC out-

puts 0 and 1 remain in their previous state.

Output-Data Format

Figures 6–9 illustrate the conversion timing for the

MAX1221/MAX1223/MAX1343. All 12-bit conversion

results are output in 2-byte format, MSB first, with four

leading zeros. Data appears on DOUT on the falling

edges of SCLK. Data is binary for unipolar mode and

two’s complement for bipolar mode and temperature

results. See Figures 3, 4, and 5 for input/output and

temperature-transfer functions.

ADC Transfer Functions

Figure 3 shows the unipolar transfer function for single-

ended or differential inputs. Figure 4 shows the bipolar

transfer function for differential inputs. Code transitions

occur halfway between successive-integer LSB values.

Output coding is binary, with 1 LSB = VREF1 / 4096 for

unipolar and bipolar operation, and 1 LSB = +0.125°C

for temperature measurements. Bipolar true-differential

results and temperature-sensor results are available in

two’s complement format, while all others are in binary.

See Tables 6, 7, and 8 for details on which setting

(unipolar or bipolar) takes precedence.

In unipolar mode, AIN+ can exceed AIN- by up to

VREF1. In bipolar mode, either input can exceed the

other by up to VREF1 / 2.

Partial Reads and Partial Writes

If the first byte of an entry in the FIFO is partially read

(

CS is pulled high after fewer than eight SCLK cycles),

the remaining bits are lost for that byte. The next byte of

data that is read out contains the next 8 bits. If the first

byte of an entry in the FIFO is read out fully, but the

second byte is read out partially, the rest of that byte is

lost. The remaining data in the FIFO is unaffected and

can be read out normally after taking

CS low again, as

long as the 4 leading bits (normally zeros) are ignored.

CS is pulled low before EOC goes low, a conversion

may not be completed and the FIFO data may not be

correct. Incorrect writes (pulling

CS high before com-

pleting eight SCLK cycles) are ignored and the register

remains unchanged.

FULL-SCALE

TRANSITION

111....111

INPUT VOLTAGE (LSB)

FS = VREF

111....110

111....101

000....011

000....010

000....001

000....000

1 LSB = VREF / 4096

FS - 3/2 LSB

Figure 3. Unipolar Transfer Function—Full Scale (FS) = VREF

OUTPUT CODE

011....111

TEMPERATURE (

°C)

011....110

000....001

111....101

100....001

100....000

111....111

111....110

000....000

000....010

-256

+255.5

Figure 5. Temperature Transfer Function

011....111

-FS

INPUT VOLTAGE (LSB)

FS = VREF / 2 + VCOM

VREF = VREF+ - VREF-

-FS = -VREF / 2

011....110

011....101

000....001

000....000

111....111

100....011

100....010

100....001

100....000

(COM)

-1

+FS - 1 LSB

1 LSB = VREF / 4096

ZS = COM

VREF

(COM)

VREF

Figure 4. Bipolar Transfer Function—Full Scale (±FS) = ±VREF / 2

MAX1221 Datasheet(PDF) 33 Page - Maxim Integrated Products

MAX1221 Datasheet(HTML) 33 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Download

Link URL