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MAX1203ACAP-T

5V, 8-Channel, Serial, 12-Bit ADCs with 3V Digital Interface

Maxim Integrated 

MAX1202/MAX1203

5V, 8-Channel, Serial, 12-Bit ADCs

with 3V Digital Interface

Track/Hold

The T/H enters tracking mode on the falling clock edge

after the fifth bit of the 8-bit control word is shifted in. The

T/H enters hold mode on the falling clock edge after the

eighth bit of the control word is shifted in. IN- is connected

to GND if the converter is set up for single-ended inputs,

and the converter samples the “+” input. IN- connects to

the “-” input if the converter is set up for differential inputs,

and the difference of |N+ - IN-| is sampled. The positive

input connects back to IN+, at the end of the conversion,

and CHOLD charges to the input signal.

The time required for the T/H to acquire an input signal is

a function of how quickly its input capacitance is charged.

If the input signal’s source impedance is high, acquisition

time increases and more time must be allowed between

conversions. The acquisition time, tACQ, is the maximum

time the device takes to acquire the signal, and is also the

minimum time needed for the signal to be acquired. It is

calculated by the following:

tACQ = 9 x (RS + RIN) x 16pF

where RIN = 9kΩ, RS = the source impedance of the input

signal, and tACQ is never less than 1.5μs. Source imped-

ances below 1kΩ do not significantly affect the ADC’s AC

performance. Higher source impedances can be used if

an input capacitor is connected to the analog inputs, as

shown in Figure 5. Note that the input capacitor forms

an RC filter with the input source impedance, limiting the

ADC’s signal bandwidth.

12-BIT CAPACITIVE DAC

REF

INPUT CHOLD

COMPARATOR

CH0

MUX –

+

ZERO

CH1

16pF

CH2

9kΩ

CH3

CSWITCH

RIN

CH4

HOLD

CH5

TRACK

AT THE SAMPLING INSTANT,

CH6

CH7

T/H

SWITCH

THE MUX INPUT SWITCHES

FROM THE SELECTED IN+

CHANNEL TO THE SELECTED

GND

IN- CHANNEL.

SINGLE-ENDED MODE: IN+ = CHO–CH7, IN- = GND.

DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF

CH0/CH1, CH2/CH3, CH4/CH5, CH6/CH7.

Figure 4. Equivalent Input Circuit

+3V

VL

0.1µF

VDD

0.1µF

GND

0 TO

4.096V

ANALOG 0.01µF

INPUT

MAX1202

VSS

MAX1203

CH7

CS

SCLK

C2

0.01µF

C1

4.7µF

REFADJ

REF

DIN

SSTRB

DOUT

SHDN

+2.5V +2.5V **

REFERENCE

+3V

N.C.***

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

**REQUIRED FOR MAX1203 ONLY.

***NO CONNECTION

Figure 5. Quick-Look Circuit

+5V

4.7µF

2MHz

OSCILLATOR

OSCILLOSCOPE

SCLK

SSTRB

DOUT*

CH1

CH2

CH3

CH4

www.maximintegrated.com

Maxim Integrated │  10

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