22

LTC1594/LTC1598

15948fb

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

Using the MUXOUT/ADCIN Loop of the LTC1598 to Form a PGA with Eight Gains in a Noninverting Configuration

is the summation of the resistors below the selected MUX

0. Table 1 shows the gain for each MUX channel. The

LT1368 dual rail-to-rail op amp is designed to operate with

0.1

μFloadcapacitors.Thesecapacitorsprovidefrequency

compensation for the amplifiers, help reduce the amplifi-

ers’ output impedance and improve supply rejection at

of the selected channel will not affect the loop gain given

by the formula above.

1594/98 TA06

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

20

21

22

23

24

1

2

3

64R

32R

16R

8R

4R

2R

R

R

+

–

8

COM

18

MUXOUT

GND

4, 9

10

6

5, 14

11

7

CSADC

CSMUX

CLK

12

13

NC

NC

12-BIT

SAMPLING

ADC

8-CHANNEL

MUX

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

LTC1391

5V

1

mF

ADCIN

17

16

15, 19

1

mF

0.1

mF

5V

1

mF

5V

–

+

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

V+

D

V–

CS

CLK

GND

1/2 LT1368

LTC1598

mP/mC