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ADC1x1S626

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LMP7312

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LMP7312

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SNOSB32B – MARCH 2010 – REVISED MARCH 2013

Figure 39. Daisy Chain

Shared 4-wire SPI with ADC

The LMP7312 is a good choice when interfacing to differential analog to digital converters ADC141S626 and

ADC161S626 of PowerWise® Family. Its SPI interface has been designed to enable sharing CSB with the ADC.

LMP7312 register access happens only when CSB is asserted low while SCK is high. However, the ADC starts

conversion under any of the following conditions:

1. CSB goes low while SCK is high

2. CSB goes low while SCK is low

3. CSB and SCK both going low

Therefore, if a system uses timing condition #2 above, LMP7312 and ADC1x1S626 can share CSB and SCK as

shown in Figure 40. The only side-effect would be that writing to LMP7312 triggers an ADC conversion, but then

the result can be ignored. At other times, the LMP7312 is not affected by the CSB assertions used to initiate

normal ADC conversions.

Figure 40. 4-wire SPI with ADC interface

LMP7312 IN 4-20mA CURRENT LOOP APPLICATION

The 4-20mA current loop shown in Figure 41 is a common method of transmitting sensor information in many

industrial process-monitoring applications. Transmitting sensor information via a current loop is particularly useful

when the information has to be sent to a remote location over long distances (1000 feet, or more). The loop’s

operation is straightforward: a sensor’s output voltage is first converted to a proportional current, with 4mA

normally representing the sensor’s zero-level output, and 20mA representing the sensor’s full-scale output. Then,

a receiver at the remote end converts the 4-20mA current back into a voltage which in turn can be further

processed by a computer or display module. A typical 4-20mA current-loop circuit is made up of four individual

elements: a sensor/transducer; a voltage-to-current converter (commonly referred to as a transmitter and/or

signal conditioner); a loop power supply; and a receiver/monitor. In loop powered applications, all four elements

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