Datasheet LTC1594, LTC1598 (Analog Devices) - 22

LTC1594/LTC1598
U TYPICAL APPLICATIONS N Using MUXOUT/ADCIN Loop as PGA
is the summation of the resistors below the selected MUX channel. If CH0 is selected, the loop gain is 1 since R This figure shows the LTC1598’s MUXOUT/ADCIN loop S1 is 0. Table 1 shows the gain for each MUX channel. The and an LT1368 being used to create a single channel PGA LT1368 dual rail-to-rail op amp is designed to operate with with eight noninverting gains. Combined with the LTC1391, 0.1μF load capacitors. These capacitors provide frequency the system can expand to eight channels and eight gains compensation for the amplifiers, help reduce the amplifi- for each channel. Using the LTC1594, the PGA is reduced ers’ output impedance and improve supply rejection at to four gains. The output of the LT1368 drives the ADCIN high frequencies. Because the LT1368’s I and the resistor ladder. The resistors above the selected B is low, the RON of the selected channel will not affect the loop gain given MUX channel form the feedback for the LT1368. The loop by the formula above. gain for this amplifier is RS1/RS2 + 1. RS1 is the summation of the resistors above the selected MUX channel and RS2
Using the MUXOUT/ADCIN Loop of the LTC1598 to Form a PGA with Eight Gains in a Noninverting Configuration
5V 5V LTC1391 1mF 1 16 CH0 V+ 1mF 2 15 CH1 D + 3 14 CH2 V– 1/2 LT1368 5V 4 13 CH3 D 0.1 OUT mF 5 12 – CH4 DIN 6 11 17 16 15, 19 1mF CH5 CS ADCIN V 7 10 REF VCC CH6 CLK 64R 20 CH0 8 9 CH7 GND 32R 21 CH1 10 CSADC 16R 22 CH2 6 CSMUX 8R 23 CH3 8-CHANNEL 12-BIT 5, 14 MUX + CLK 4R 24 CH4 SAMPLING 11 mP/mC ADC DOUT 2R 1 CH5 7 – DIN R 2 CH6 R 3 CH7 LTC1598 12 18 MUXOUT NC 8 COM 13 NC GND 4, 9 1594/98 TA06 15948fb 22