MAX197 Maxim, MAX197 Datasheet - Page 8

• Manufacturer Part Number: MAX197
• Description: Multi-Range (10V / 5V / +10V / +5V) / Single +5V / 12-Bit DAS with 8+4 Bus Interface
• Manufacturer: Maxim

The MAX197, a multi-range, fault-tolerant ADC, uses
successive approximation and internal input track/hold
(T/H) circuitry to convert an analog signal to a 12-bit
digital output. The parallel-output format provides easy
interface to microprocessors (µPs). Figure 3 shows the
MAX197 in its simplest operational configuration.
In the internal acquisition control mode (control bit D5
set to 0), the T/H enters its tracking mode on WR’s ris-
ing edge, and enters its hold mode when the internally
timed (6 clock cycles) acquisition interval ends. A low
impedance input source, which settles in less than
1.5µs, is required to maintain conversion accuracy at
the maximum conversion rate.
In the external acquisition control mode (D5 = 1), the
T/H enters its tracking mode on the first WR rising edge
and enters its hold mode when it detects the second WR
rising edge with D5 = 0. See the External Acquisition
section.
The ADC’s input tracking circuitry has a 5MHz small-
signal bandwidth. When using the internal acquisition
Multi-Range (±10V, ±5V, +10V, +5V),
Single +5V, 12-Bit DAS with 8+4 Bus Interface
Figure 3. Operational Diagram
8
_______________Detailed Description
CONTROL
INPUTS
_______________________________________________________________________________________
P
P DATA BUS
100pF
10
11
12
13
14
1
2
3
4
5
6
7
8
9
WR
RD
D6
D1/D9
CLK
CS
HBEN
SHDN
D7
D5
D4
D3/D11
D2/D10
D0/D8
MAX197
Analog-Input Track/Hold
REFADJ
Converter Operation
DGND
AGND
CH7
CH6
CH5
CH4
CH3
CH2
CH1
CH0
V
REF
INT
DD
Input Bandwidth
28
27
26
25
24
23
22
21
20
19
18
17
16
15
0.1 F
OUTPUT STATUS
ANALOG
INPUTS
+4.096V
4.7 F
+5V
mode with an external clock frequency of 2MHz, a
100ksps throughput rate can be achieved. It is possible
to digitize high-speed transient events and measure
periodic signals with bandwidths exceeding the ADC’s
sampling rate by using undersampling techniques. To
avoid high-frequency signals being aliased into the fre-
quency band of interest, anti-alias filtering is recom-
mended (MAX274/MAX275 continuous-time filters).
Figure 4 shows the equivalent input circuit. With V
4.096V, the MAX197 can be programmed for input
ranges of ±10V, ±5V, 0V to 10V, or 0V to 5V by setting the
appropriate control bits (D3, D4) in the control byte (see
Tables 2 and 3). The full-scale input voltage depends on
the voltage at REF (Table 1). When an external reference
is applied at REFADJ, the voltage at REF is given by V
= 1.6384 x V
Table 1. Full Scale and Zero Scale
Figure 4. Equivalent Input Circuit
RANGE (V) ZERO SCALE (V) -FULL SCALE +FULL SCALE
CH_
0 to 10
S1 = BIPOLAR/UNIPOLAR SWITCH
S2 = INPUT MUX SWITCH
S3, S4 = T/H SWITCH
0 to 5
±10
±5
12.5k
REFADJ
5.12k
—
—
0
0
S1
S2
8.67k
(2.4V < V
Input Range and Protection
HOLD
UNIPOLAR
BIPOLAR
OFF
ON
-V
-V
REF
REF
REF
S3
< 4.18V).
—
—
x 1.2207 V
x 2.4414 V
TRACK
C
HOLD
TRACK
V
V
S4
REF
REF
REF
REF
VOLTAGE
REFERENCE
x 1.2207
x 2.4414
x 1.2207
x 2.4414
T/H
OUT
REF
HOLD
REF
=