L9663 datasheet(40/104 Pages) STMICROELECTRONICS

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Satellite interface

L9663

40/104

DocID028693 Rev 1

3.7.5

Cross coupling test

An automatic hardware based cross-coupling test (XCT) for the PSI interfaces is

implemented and can be triggered by SPI command (Self-Test Setting (STS) Register). Aim

of the test is to monitor the status of PSIx interfaces both in master and slave mode; slave

mode simply checks that when PSIx are switched off the under voltage flag is set, while

master mode implements a Finite State Machine able to schedule several steps (see

description below).



XCT test both in master and slave mode is triggered only if both PSIx interfaces are off.

In case one of the PSI-IFs is already switched on, starting of a XCT will not be possible

and in this case the XCT results register will be reset.



Once XCT test is running, commands to switch the channel on or disable VAS regulator

are ignored by the device.



Once XCT test is running, it cannot be interrupted or stopped by any SPI instruction

except by stop bit within "Abort cross-coupling test" command: in this case, only in

master mode, an "abort" flag will be set (XCT_ABT bit).



While XCT test is running a "busy" flag will be asserted (XCT_RUN bit).



Once XCT test is finished a "done" flag will be asserted (XCT_COMPL).



Flag "busy" is only asserted while XCT test both master and slave mode is ongoing

while "done", "abort", XCTx_R, STB, XCT_STG results are cleared when read via SPI

or when a new XCT start request occurs (both valid or invalid). Please note that

XCT_STG bits are mapped in bits 0 and bit 8 of SR2 register. These bits normally are

real time bits but, as soon as a Master XCT test is completed (and the XCT_COMPL

flag is asserted) the bits 0 and 8 contain the results of the XCT test and keep this value

until results are cleared by reading or by new test start)

Slave Mode (PSIx switched off)



A pulldown current (IXCT) is turned ON for both channels for a 512 μs time in order to

be sure to discharge PSI5 lines



Once PSI5 line is supposed to be discharged (512 μs time elapsed), pull-down current

is switched off on each channel



Check psi1_uv=psi2_uv='1':

–

Xcoupling_slave PSI1 ok if psi1_uv='1' (test failed otherwise)

–

Xcoupling_slave PSI2 ok if psi2_uv='1' (test failed otherwise)

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