L99MH98 datasheet(37/147 Pages) STMICROELECTRONICS

37 / 147 page

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Comparator for the high-side (HS) and low-side (LS) drain-source voltage monitoring

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The checked node can go up or down and it is not bounded to the pull-up value of the off state

Ishx_PU and Ishx_PD can be activated for each half-bridge only if the bridge driver is in active mode as set by the

control bits OUTEx, x = 1…8. Also Ishx_PU and Ishx_PD can be activated only when the off-state diagnostic is

enabled by the microcontroller.

The Vds comparators change their state after a filter time called tDIAG. The faults in the DSRx are not latched and

the configurations placed in the registers are bypassed during diag off.

The Ishx_PU ,and Ishx_PD values can be selected by using the DIAGOFF_CURR_SEL register.

The L99MH98 determines the voltage at SHx, using the drain-source overvoltage comparators of the high-side or

low-side MOSFETs. The microcontroller can read the status bit VDS_HSx_DIAG, x = 1...8, or the status bit

VDS_LSx_DIAG, x = 1...8 to determine if VSHx is high or low.

The diagnostic process is controlled by the microcontroller, whose task is:

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To activate and deactivate Ishx_PU and Ishx_PD, controlled by the HB_IDIAGx registers

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To read and interpret the status bits VDS_LSx_DIAG and VDS_HSx_DIAG

The following conditions are equivalent in the rest of this document:

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VDS_HSx_DIAG = VDS_LSx_DIAG = 0: SHx is low

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VDS_HSx_DIAG = VDS_LSx_DIAG = 1: SHx is high

5.4.2

Example with a DC motor controlled by two half-bridges

This section gives an example of an off-state diagnostic with one DC motor controlled by the half-bridges 1 and 2.

The voltages at SH1/SH2 (noted VSH1/VSH2) are analyzed in the following test configurations:

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Configuration 1

Ishx_PU HB1 OFF, Ishx_PU HB2 OFF, Ishx_PD HB1 ON, Ishx_PD HB2 ON

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Configuration 2

Ishx_PU HB1 ON, Ishx_PU HB2 OFF, Ishx_PD HB1 OFF, Ishx_PD HB2 ON

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Configuration 3

Ishx_PU HB1 OFF, Ishx_PU HB2 ON, Ishx_PD HB1 ON, Ishx_PD HB2 OFF

Figure 20. Simplified block diagram with one DC motor controlled by two half-bridges

VDS_HSx

VDS_HSx_DIAG

VDS_LSx

VDS_LSx_DIAG

VDH

GND

VSHx_OL

IPD

IPU

IPD

IPU

SH1

SH2

GND

VSHx_OL

VDS_HSx

VDS_HSx_DIAG

VDS_LSx

VDS_LSx_DIAG

GH1

GL1

GH2

GL2

VODLS = 1.8 V

VODHS = 1.8 V

5.4.3

Normal load conditions

Configuration 1

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Ishx_PU HB1 OFF, Ishx_PD HB1 ON

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Ishx_PU HB2 OFF, Ishx_PD HB2 ON

In normal conditions, the motor is connected between SH1 and SH2 without any short circuit.

If Ishx_PU of HB1 and HB2 are off, the SH1 and SH2 are pulled down by Ishx_PD of HB1 and HB2 (see the

Figure 21), so VDS_LS1 = VDS_LS2 = LOW and VDS_HS1 = VDS_HS2 = HIGH.

L99MH98

Protections and diagnostics

DS14611 - Rev 3

page 37/147

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