MAX1204 Datasheet, PDF (9/24 Pages) Maxim Integrated Products – 5v, 8-cHANNEL, sERIAL, 10-bIT adc WITH 3v dIGITAL iNTERFACE

5V, 8-Channel, Serial, 10-Bit ADC
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 connect-
ed to GND if the converter is set up for single-ended
inputs, and the converter samples the “+” input. IN- con-
nects to the “-” input if the converter is set up for differen-
tial inputs, and the difference of  |N+ - IN- is sampled.
The positive input connects back to IN+ at the end of
the conversion, and C_HOLD 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,
t_ACQ, 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:
t_ACQ = 7 x (R_S + R_IN) x 16pF
where R_IN = 9kΩ, R_S = the source impedance of the
input signal, and t_ACQ is never less than 1.5µs. Note that
source impedances below 4kΩdo 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 imped-
ance, limiting the ADC’s signal bandwidth.
CAPACITIVE DAC
REF
INPUT C_HOLD
COMPARATOR
CH0
MUX _–
+
ZERO
CH1
16pF
CH2
9k
CH3
C_SWITCH
R_IN
CH4
HOLD
TRACK
CH5
AT THE SAMPLING INSTANT,
CH6
THE MUX INPUT SWITCHES
T/H
FROM THE SELECTED IN+
CH7
SWITCH
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
V_DD
0.1µF
+5V
0.1µF
OSCILLOSCOPE
GND
0V TO
4.096V
ANALOG _0.01µF
INPUT
MAX1204
V_SS
CH7
CS
SCLK
DIN
SSTRB
REFADJ
DOUT
C2
0.01µF
REF
C1
4.7µF
SHDN
+3V
N.C.
2MHz
OSCILLATOR
SCLK
SSTRB
DOUT
CH1
CH2
CH3
CH4
FULL-SCALE ANALOG INPUT
Figure 5. Quick-Look Circuit
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