L99MH98 datasheet(22/147 Pages) STMICROELECTRONICS

22 / 147 page

All the configurations shall be changed while the diagnosis/channel is not active to guarantee the correct value of

the time selected and to apply the correct configuration. If the filter is changed during the actuation the value of

the filter is not guaranteed.

3.2.4

Multi fail-safe mode

The L99MH98 integrates a so called “multi fail-safe mode”, an automatic system that intervenes to switch off

passively the gate driver/s to protect the device/application if a fault happens according to the registers settings.

In active mode, with no faults, the charge pump is enabled. The gate drivers outputs are driven according to the

OUTEx control bit: when the OUTEx control bits are reset, all the gate drivers are low and the external MOSFETs

are strongly shut off through the internal predriver pulldown. An additional passive pulldown connected between

gate and GND and between source and GND of each MOSFET is present.

Once the OUTEx control bit is set, each HS and LS MOSFETs of the 8 half-bridges x, x = 1...8, can be:

•

Deactivated

•

Activated (statically, no PWM)

•

Activated in PWM mode

The HB_MODEx registers are used to control the functionality of the single half-bridge. x indicates the number of

the half-bridge to work on, x = 1 to 8. It is a 2-bit register, see the Table 21 and Table 23.

Table 21. HB_MODEx register functionality

HB_MODEx, x = 1...8

Setting

LS and HS of the half-bridge x are kept in DIAG OFF state (default)

LS of the half-bridge x is ON (static, no PWM), HS of the half-bridge x is OFF

HS of the half-bridge x is ON (static, no PWM), LS of the half-bridge x is OFF

LS or HS of the half-bridge x is ON according to the HB_PWMx, x=1…8, register

When a fault condition is detected, the behavior of the device is different depending on the cause of the fault

itself.

When the VDH supply input voltage rises above the programmable overvoltage protection threshold (VDHOVT1 for

OVTS = 0 or VDHOVT2 for OVTS = 1) for a time longer than tOV_FILT, the corresponding overvoltage flag (VDHOV)

is set to protect the application.

The overvoltage protection flag VDHOV can be cleared by an SPI “read and clear” command only if the VDH

overvoltage condition is no longer present, namely if the foresaid condition that automatically enables the charge

pump is fulfilled.

The following actions can be taken:

•

The charge pump is left on. The external MOSFETs are switched off. In particular, the external HS and the

LS MOSFETs are forced off actively with the maximum available current, regardless of the programmed

gate discharge current. This working mode is obtained setting the GENMODEx = 0, x = 1...8

•

In this second case, called GENERATOR MODE, the charge pump is left on. The HS external MOSFETs

are switched off. The LS MOSFETs are switched on to lock the motor. This working mode is obtained

setting the GENMODEx = 1, x = 1…8

•

In this working mode the charge pump and the external MOSFETs are not switched off. L99MH98

continues to work waiting for an interrupt from the microcontroller that will decide how to proceed. This

working mode is obtained setting the GENMODEx = 2, x = 1...8

In the event of a fault due to VDD overvoltage, thermal shutdown, watchdog event, the flag relating to the fault is

set and the external MOSFETs, together with the charge pump are switched off to protect the device.

In case the VDD overvoltage condition is no longer present after the filtering time tOV_FLT, the charge pump is

switched on again, while the other functions are kept off until the VDDOV flag is cleared.

When a Vds monitoring failure event occurs, the half-bridge in which the Vds monitoring failure occurred is

switched off. In addition to the half-bridge in which the failure occurred, all half-bridges that are connected to the

one that failed are also turned off. L99MH98 is able to turn off only the half-bridges connected to each other in

accordance with what is written in the HB_FAULTx, x = 1…8, register: at each half-bridge is assigned a key

whose values can be 0, 1, 2, 4 or 8, as shown in the Figure 6:

•

0 = the HBx is not connected to the other half-bridges;

L99MH98

Functional description

DS14611 - Rev 3

page 22/147

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