32-Channel Sample/Hold Amplifier

with Four Multiplexed Inputs

8

_______________________________________________________________________________________

MODE

SELECT

ADDRESS

(A0–A2)

OUTPUT

INPUT

HOLD STEP

Figure 2. Timing Performance

__________Applications Information

Combining Inputs

The MAX5166 contains a separate input for each 1-to-8

multiplexer. Externally connect the input pins to form

larger multiplexers. When all four inputs are connected

to the same source, the MAX5166 is functionally equiv-

alent to the MAX5165, except the MAX5166 does not

contain output clamping diodes.

Control-Line Reduction

The MAX5166 contains four separate 1-to-8 multiplexers

and individual mode selectors for each multiplexer. When

sampling one channel at a time, use an external 2-to-4

decoder (with active-low outputs) to reduce the number

of digital control lines from seven to five (Figure 3).

Single vs. Simultaneous Sampling

Individually control the four mode/multiplexer-select

pins to simultaneously sample on four channels, the

same channel for each multiplexer (Figure 4). Each

mode-select pin controls sampling on one of the 1-to-8

multiplexers, while the 3-bit address selects one of the

eight channels on all the multiplexers (Tables 1 and 2).

Setting any combination of the mode-select pin low

enables sampling on the addressed channels for the

selected multiplexers.

Simultaneously sampling two or more channels reduces

offset voltage but increases acquisition time. Multiply

the single-channel acquisition time by the number of

channels sampling.

Multiplexed DAC

Figure 5 shows a typical demultiplexer application.

Different digital codes are converted by the digital-to-

analog converter (DAC) and then stored on eight differ-

ent channels, or as many as 32 different channels

when all four inputs are active. The 100mV/sec (max)

droop rate requires refreshing the hold capacitors

every 100ms before the voltage drops by 1/2LSB for an

8-bit DAC with a 5V full-scale voltage.

Powering the MAX5166

The MAX5166 does not require a special power-up

sequence to avoid latchup. The device requires three

separate supply voltages for operation; however, when

one or two of the voltages are not available, DC-DC

charge-pump (switched-capacitor) converters provide

a simple, efficient solution. The MAX860 provides volt-

age doubling or inversion, ideal for conversions from

+5V to +10V or from +5V to -5V. The MAX860 also

functions as a voltage divider to provide conversion

from +10V to +5V.