LTC1598 LINER [Linear Technology], LTC1598 Datasheet - Page 22

• Manufacturer Part Number: LTC1598
• Description: 4- and 8-Channel, Micropower Sampling 12-Bit Serial I/O A/D Converters
• Manufacturer: LINER [Linear Technology]

LTC1594/LTC1598
TYPICAL APPLICATIONS
Using MUXOUT/ADCIN Loop as PGA
This figure shows the LTC1598’s MUXOUT/ADCIN loop
and an LT1368 being used to create a single channel PGA
with eight noninverting gains. Combined with the LTC1391,
the system can expand to eight channels and eight gains
for each channel. Using the LTC1594, the PGA is reduced
to four gains. The output of the LT1368 drives the ADCIN
and the resistor ladder. The resistors above the selected
MUX channel form the feedback for the LT1368. The loop
gain for this amplifier is R
of the resistors above the selected MUX channel and R
22
1
2
3
4
5
6
7
8
Using the MUXOUT/ADCIN Loop of the LTC1598 to Form a PGA with Eight Gains in a Noninverting Configuration
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
LTC1391
D
GND
CLK
OUT
D
V –
CS
V +
IN
D
16
15
14
13
12
11
10
9
5V
S1
/R
1 F
S2
+
–
1/2 LT1368
+ 1. R
64R
32R
16R
U
5V
8R
4R
2R
R
R
S1
N
is the summation
1 F
20
21
22
23
24
18 MUXOUT
1
2
3
8 COM
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
0.1 F
8-CHANNEL
S2
MUX
is the summation of the resistors below the selected MUX
channel. If CH0 is selected, the loop gain is 1 since R
0. Table 1 shows the gain for each MUX channel. The
LT1368 dual rail-to-rail op amp is designed to operate with
0.1μF load capacitors. These capacitors provide frequency
compensation for the amplifiers, help reduce the amplifi-
ers’ output impedance and improve supply rejection at
high frequencies. Because the LT1368’s I
of the selected channel will not affect the loop gain given
by the formula above.
17
ADCIN
+
SAMPLING
–
LTC1598
12-BIT
GND
ADC
16
V
4, 9
REF
V
CC
15, 19
CSMUX
CSADC
D
CLK
OUT
D
NC
NC
IN
10
6
5, 14
11
7
12
13
5V
1 F
1594/98 TA06
B
is low, the R
P/ C
15948fb
S1
ON
is