MAX1202 Datasheet, PDF (10/24 Pages) Maxim Integrated Products – 5v, 8-cHANNEL, sERIAL, 12-bIT adcS WITH 3v dIGITAL iNTERFACE

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 con-
nected 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 = 9 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. Source
impedances 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 capaci-
tor forms an RC filter with the input source impedance,
limiting the ADC’s signal bandwidth.
12-BIT 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
0.1µF
V_DD
+5V
0.1µF
4.7µF
GND
OSCILLOSCOPE
0V TO
4.096V
ANALOG _0.01µF
INPUT
C2
0.01µF
C1
4.7µF
MAX1202
V_SS
MAX1203
CH7
CS
SCLK
REFADJ
REF
DIN
SSTRB
DOUT
SHDN
+2.5V _+2.5V **
REFERENCE
+3V
N.C.
2MHz
OSCILLATOR
CH1
CH2
CH3
CH4
*FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FFF (HEX).
**REQUIRED FOR MAX1203 ONLY.
Figure 5. Quick-Look Circuit
10 ______________________________________________________________________________________
SCLK
SSTRB
DOUT*