Datasheet LTC1391 (Analog Devices) - 7

LTC1391
U U W U APPLICATIONS INFORMATION
bits clocked into the LTC1391 shift register before CS is To ensure that only one channel is switched on at any one taken low select the MUX channel that is turned on. This time, two sets of channel selection bits are needed for allows a series of devices, with the D DATA as shown in Figure 6. The first data sequence is used OUT of one device connected to the D to switch off one MUX and the second data sequence is IN of the next device, to be programmed with a single data stream. used to select one channel from the other MUX or vice versa. In other words, if bit “ENA” is high and bit “ENB” is low, one channel of MUX A is switched on and all CLK 1 2 3 4 channels of MUX B are switched off. If bit “ENA” is low and bit “ENB” is high, all channels at MUX A are switched off DIN D1 D2 D3 D4 D5 and one channel of MUX B is switched on. Care should be taken to ensure that only one LTC1391 is enabled at any D one time to prevent two channels from being enabled OUT D1 D2 D3 D4 D5 simultaneously. 1391 • F04
Figure 4. Digital Data Transfer Operation
CLK 1 2 3 4 5 6 7 8
Multiplexer Expansion
CS Several LTC1391s can be daisy-chained to expand the number of multiplexer inputs. No additional interface ports are required for the expansion. Figure 5 shows two D ENA A2 A1 A0 ENB B2 B1 B0 IN 1391 • F06 LTC1391s connected at their analog outputs to form a 16-to-1 multiplexer at the input to an LTC1400 A/D converter.
Figure 6. Data Sequence for MUX Expansion
5V –5V 5V + 0.1µF 0.1µF 0.1µF 10µF OPTIONAL A/D 1 16 1 8 S0 V+ INPUT FILTER V V CC SS – 5V 2 15 2 7 10µF 0.1µF S1 D A CONV + IN 3 14 3 LTC1400 6 S2 V – V CLK REF + 4 13 0.1µF 4 5 ANALOG S3 D DATA OUT 10µF LTC1391 GND DOUT INPUTS 5 12 OUT S4 A DIN 6 11 S5 CS 7 10 S6 CLK 8 9 S7 GND 1 16 S0 V+ 2 15 S1 D 3 14 S2 V – 4 13 S3 D ANALOG OUT 5 LTC1391 INPUTS 12 S4 B DIN DATA IN 6 11 S5 CS CS 7 10 S6 CLK CLK 8 9 S7 GND 1391 • F05
Figure 5. Daisy-Chaining Two LTC1391s for Expansion
sn1391 1391fas 7