ML2252, ML2259

7

1.0 FUNCTIONAL DESCRIPTION

1.1 MULTIPLEXER ADDRESSING

The ML2252 and ML2259 contain a single ended analog

multiplexer. A particular input channel is selected by

using the address decoder. The relationship between the

address inputs, ADDR0–ADDR2, and the analog input

selected is shown in Table 1. The address inputs are

latched into the decoder on the rising edge of the address

latch signal ALE.

ML2252

SELECTED

ADDRESS

ANALOG CHANNEL

INPUT

CH0

0

CH1

1

ML2259

SELECTED

ADDRESS INPUT

ANALOG CHANNEL

ADDR2

ADDR1

ADDR0

CH0

0

0

0

CH1

0

0

1

CH2

0

1

0

CH3

0

1

1

CH4

1

0

0

CH5

1

0

1

CH6

1

1

0

CH7

1

1

1

Table 1. Multiplexer Address Decoding

1.2 A/D CONVERTER

The A/D converter uses successive approximation to

perform the conversion. The converter is composed of the

successive approximation register, the DAC and the

comparator.

The DAC generates the precise levels that determine the

linearity and accuracy of the conversion. The DAC is

composed of a capacitor upper array and a resistor lower

array. The capacitor upper array generates the 4 MSB

decision levels while the series resistor lower array

generates the 4 LSB decision levels. A switch decoder tree

is used to decode the proper level from both arrays.

The capacitor/resistor array offers fast conversion, superior

linearity and accuracy since matching is only required

elements in conventional designs). And since the levels are

based on the ratio of capacitors to capacitors and resistors to

resistors, the accuracy and long term stability of the

converter is improved. This also guarantees monotonicity

and no missing codes, as well as eliminating any linearity

temperature or power supply dependence.

The successive approximation register is a digital block

used to store the bit decisions from the conversion.

The comparator design is unique in that it is fully

differential and auto zeroed. The fully differential

architecture provides excellent noise immunity, excellent

power supply rejection, and wide common mode range. The

comparator is auto zeroed at the start of each conversion in

order to remove any DC offset and full scale gain error, thus

improving accuracy and linearity.

1

0.75

0.5

0.25

0

01

2

3

4

5

25°C

2

1.5

1

0.5

0

01

2

3

4

5