L9658 datasheet(28/64 Pages) STMICROELECTRONICS

28 / 64 page

Functional description

L9658

28/64

Doc ID 14219 Rev 3

4.10.5

Resistance measurement

During a resistance measurement, both ISRC and ISINK are switched on. An analog

voltage on AOUT pin is provided. AOUT pin is a 5 V analog pin, which will be connected to the

ADC input of a processor. This pin provides the resistance-measurement voltage, which

correspond to the voltage difference across SQH and SQL. According to the following

formula:

Vaout = VDD/10 + Rsquib · Isrc · 10

The accuracy in the range of Rsquib is classified as followings:

0 < Rsquib  3.5 

±95 mV

3.5 < Rsquib  10 

±5 %

A low pass filter (10 k

 + 330 pF) is recommended in order to cancel noise caused by

internal offset compensation.

Figure 15.

Resistance measurement flow chart

4.10.6

MOS diagnostics

During diagnostic, IBIAS is connected to SQH pin. In a normal condition, SQH voltage is

below SBTH and SQL voltage will be higher than SGTH. Prior to turning on the MOS, the

processor is expected to check for a short to battery and a short to ground fault. This step is

intended to prevent a large amount of current flowing through the MOS. Also, this step is

intended to precondition SQH and SQL pins prior to diagnostics. DEPEN pin is asserted in

order to turn on the low or high side driver. If DEPEN is negated during diagnostic, the MOS

is not turned on and a fail MOS diagnostic is expected.

4.10.7

Low side MOS diagnostic

When L9658 receives a SPI command to initiate the low side driver diagnostic, verification

of following conditions are done before turning on the low side driver:

–VSQL greater than SGTH threshold voltage

–VSQH less than SBTH threshold voltage

If both conditions above are satisfied, execution of low side driver diagnostic is performed.

Otherwise, the low side MOS diagnostic request is ignored and both bit D13 and bit D7 in

SPI diagnostic mode response are set. Upon detection of the following conditions, the

BEGIN

END

SPI Command:

Enable AOUT,

Turn on I

SRC & ISINK

SPI Command:

Turn off ISRC & ISINK

Turn off I

SRC & ISINK

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