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LTC2404I Datasheet(PDF) 17 Page - Linear Technology |
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LTC2404I Datasheet(HTML) 17 Page - Linear Technology |
17 / 36 page 17 LTC2404/LTC2408 APPLICATIONS INFORMATION Table 5. LTC2404/LTC2408 Interface Timing Modes Conversion Data Connection SCK Cycle Output and Configuration Source Control Control Waveforms External SCK External CS and SCK CS and SCK Figures 7, 8, 9 Internal SCK Internal CS ↓ CS ↓ Figures 10, 11 is used as an end of conversion indicator during the conversion and sleep states. When CSADC (Pin 23) is HIGH, the SDO driver is switched to a high impedance state. This allows sharing the serial interface with other devices. If CSADC is LOW during the convert or sleep state, SDO will output EOC. If CSADC is LOW during the conversion phase, the EOC bit appears HIGH on the SDO pin. Once the conversion is complete, EOC goes LOW. The device remains in the sleep state until the first rising edge of SCK occurs while CSADC = 0. ADC Chip Select Input (CSADC) The active LOW chip select, CSADC (Pin 23), is used to test the conversion status and to enable the data output transfer as described in the previous sections. In addition, the CSADC signal can be used to trigger a new conversion cycle before the entire serial data transfer has been completed. The LTC2404/LTC2408 will abort any serial data transfer in progress and start a new conversion cycle anytime a LOW-to-HIGH transition is detected at the CSADC pin after the converter has entered the data output state (i.e., after the first rising edge of SCK occurs with CSADC = 0). Multiplexer Chip Select (CSMUX) For 4-wire operation, this pin is tied directly to CSADC or the output of an inverter tied to CSADC. CSMUX (Pin 20) is driven HIGH during selection of a multiplexer channel. On the falling edge of CSMUX, the selected channel is enabled and drives MUXOUT. Data Input (DIN) The data input to the multiplexer, DIN (Pin 21), is used to program the multiplexer. The input channel is selected by serially shifting a 4-bit input word into the DIN pin under the control of the multiplexer clock, CLK. Data is shifted into the multiplexer on the rising edge of CLK. Table 3 shows the logic table for channel selection. In order to select or change a previously programmed channel, an enable bit (DIN = 1) must proceed the 3-bit channel select serial data. The user may set DIN = 0 to continually convert on the previously selected channel. SERIAL INTERFACE TIMING MODES The LTC2404/LTC2408’s 4-wire interface is SPI and MICROWIRE compatible. This interface offers two modes of operation. These include an internal or external serial clock. The following sections describe both of these serial interface timing modes in detail. For both cases the converter can use the internal oscillator (FO = LOW or FO = HIGH) or an external oscillator connected to the FO pin. Refer to Table 5 for a summary. External Serial Clock (SPI/MICROWIRE Compatible) This timing mode uses an external serial clock (SCK) to shift out the conversion result, see Figure 7. This same external clock signal drives the CLK pin in order to pro- gram the multiplexer. A single CS signal drives both the multiplexer CSMUX and converter CSADC inputs. This common signal is used to monitor and control the state of the conversion as well as enable the channel selection. The serial clock mode is selected on the falling edge of CSADC. To select the external serial clock mode, the serial clock pin (SCK) must be LOW during each CSADC falling edge. The serial data output pin (SDO) is HI-Z as long as CSADC is HIGH. At any time during the conversion cycle, CSADC may be pulled LOW in order to monitor the state of the converter. While CSADC is LOW, EOC is output to the SDO pin. EOC = 1 while a conversion is in progress and EOC = 0 if the device is in the sleep state. Independent of CSADC, the device automatically enters the low power sleep state once the conversion is complete. |
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