Datasheet

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 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 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.
Figure 5. Quick-Look Circuit
Figure 4. Equivalent Input Circuit
0.1µF
4.7µF
V
DD
GND
V
SS
CS
SCLK
DIN
DOUT
SSTRB
SHDN
+3V
N.C.***
0.01µF
CH7
V
L
REFADJ
+2.5V
REFERENCE
REF
C2
0.01µF
C1
4.7µF
+2.5V
**
0 TO
4.096V
ANALOG
INPUT
0.1µF
+3V
OSCILLOSCOPE
CH1 CH2
CH3
CH4
*FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FFF (HEX).
**REQUIRED FOR MAX1203 ONLY.
***NO CONNECTION
MAX1202
MAX1203
+5V
2MHz
OSCILLATOR
SCLK
SSTRB
DOUT*
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
GND
C
SWITCH
TRACK
T/H
SWITCH
9kΩ
R
IN
C
HOLD
HOLD
12-BIT CAPACITIVE DAC
REF
ZERO
COMPARATOR
–
+
16pF
SINGLE-ENDED MODE: IN+ = CHO–CH7, IN- = GND.
DIFFERENTIAL MODE:
AT THE SAMPLING INSTANT,
THE MUX INPUT SWITCHES
FROM THE SELECTED IN+
CHANNEL TO THE SELECTED
IN- CHANNEL.
INPUT
MUX
IN+ AND IN- SELECTED FROM PAIRS OF
CH0/CH1, CH2/CH3, CH4/CH5, CH6/CH7.
MAX1202/MAX1203 5V, 8-Channel, Serial, 12-Bit ADCs
with 3V Digital Interface
www.maximintegrated.com
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