Rainbow Electronics MAX158 - Manual (Page 10)

MAX154/MAX158
Bipolar Input Operation
The circuit in Figure 10a can be used for bipolar input
operation. The input voltage is scaled by an amplifier
so that only positive voltages appear at the ADC’s
inputs. The analog input range is ±4V and the output
code is complementary offset binary. The ideal
input/output characteristic is shown in Figure 10b.
CMOS High-Speed 8-Bit ADCs with
Multiplexer and Reference
10 ______________________________________________________________________________________
1pF C S
12pF
C S
2pF
1pF
•
•
•
15 LSB COMPARATORS
TO LS
LADDER
R ON
1pF
1pF
•
•
•
16 MSB COMPARATORS
TO MS
LADDER
R ON
R MUX R S
V IN
AIN1
11111111
11111110
10000010
10000001
01111111
01111110
10000000
00000001
00000000
00000010
0V
AIN INPUT VOLTAGE (LSBs)
FS = 8V
1LSB = FS / 256
11111101
+FS
2
-FS + 1LSB
2
MAX154
MAX158
RD
RDY
*A2 ON MAX158.
CS
A1 A2* A0
5V
DATA BUS
A15
A0
ZBO
MREQ
WAIT
RD
DB0-DB7 D0-D7
ADDRESS
DECODE EN
5k
ADDRESS BUS
R S
V IN
AIN1
C
S1
2pF
C S2
2pF
32pF
B MUX
600 Ω
R
ON
350 Ω
MAX154
MAX158
AIN1
ONLY CHANNEL 1 SHOWN
V REF +
REFOUT
V
DD
V REF -
GND
11.5 Ω
3.57k
10.0k
0.01 µ F
0.01 µ F
0.1 µ F 47 µ F
16.2k
V IN
+5V
CS
RDY
INT
DB0-DB7
RD
Figure 9a. Equivalent Input Circuit
Figure 10b. Transfer Function for ±4V Input Operation
Figure 11. Simple Mode 0 Interface
Figure 9b. RC Network Model
Figure 10a. Bipolar ±4V Input Operation