LTM2893 datasheet(14/32 Pages) LINER

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LTM2893/LTM2893-1

28931fb

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APPLICATIONS INFORMATION

that use this function, such as the LTC2338 and LTC2328.

In order to defeat this, connect the BUSYS signal to CNV2,

and the ADCs’ BUSY signal to BUSY2. This will always

keep the ADC awake, see Figure 13.

If the sleep function is needed, a select signal (SA, SB,

or SC) can be used with 74VHC02 logic gates to disable

this keep-alive function shown in Figure 2.

Table 1. Fault Reporting

FAULTS

CAUSE/TROUBLESHOOTING

Idle time during

serial digital

interface read

during configuration

write (CSC) or

LTM2893-1

SCK↑ to SCK↑ > tWATCHDOG_TIMEOUT or SS or

CSC↓ to SCK↑ > tWATCHDOG_TIMEOUT. Minimize

delay between this relationship to less than

tWATCHDOG_TIMEOUT. SCK frequency must be

greater than the minimum referenced in Table 5.

Exceeding

configured SCKs

within a cycle

Exceeding the configured WORDLENGTH number

of SCKs during a read is considered a fault.

Data loss in isolation

communication

Common mode transients (GND to GND2) greater

than 50kV/µs. High transient EM field disturbances

greater than specified in EN61000, or an ESD event

Isolated side power

loss

ON2, VL2, or VCC2 was removed and returned.

Indicates unexpected interface loss.

CNV rising edge

during serial digital

interface read

Avoid transitioning CNV during the read of the

serial digital interface. CNV will be ignored during

the read of the serial digital interface.

SELECT SIGNALS

The select signal inputs SA, SB, and SC are communicated

to the isolated side and output on SA2, SB2, and SC2 re-

spectively. The select signals allow control of an external

device related to the acquisition of an analog input signal.

Select signals are communicated through the isolator on

edge events. A static condition at start up is not com-

municated to the isolated side. A transition is required

to exit the default low output. Examples of device types

anticipated for use on these pins are analog multiplexers

(Figure 18) or programmable gain amplifiers. The signals

can be used as logic controls for resets or power down

functionsthatarenotexpectedtooccurduringaconversion

of an analog signal. The select signals are not designed for

use as general purpose logic signals with asynchronous

transition times relative to an analog to digital conversion.

Useofthesesignalsmustbekeptsynchronousandoutside

of the operation of the CNV, BUSY, or SS active duration.

Data and time sensitive information may be lost if a select

signal transitions within 150ns of the CNV or SS signal.

Figure 2. ADC Keep-Alive and Sleep Enable

28931 F02

CNV2

BUSYS

LTM2893

BUSY2

74VHC02

ENABLE SLEEP

SA2

LTC2338-18

CNV

BUSY

IF ENABLE SLEEP = 0, BUSY SIGNALS PASS

IF ENABLE SLEEP = 1, BUSY2,S = 0 AND

TWO CNV RISING EDGES WILL PUT ADC TO SLEEP

FAULT REPORTING

The FAULT pin indicates the occurrence of an internal

communication error or an erroneous input condition.

The FAULT pin is an open drain and requires an external

pull up resistance for monitoring. If the FAULT pin is as-

serted low, data loss may have occurred and the current

transaction is suspected to contain an error. To clear the

FAULT pin, return CNV low and SS high and initiate a new

transaction with CNV or SS.

The LTM2893 does not have the provisions to provide the

reason for the fault condition. Possible fault conditions

are listed in Table 1. If the BUSY signal goes high and the

FAULT pin goes low a watchdog time out has occurred.

Theconfigurationregisterisclearedandmustberewritten.

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