L9945 datasheet(33/151 Pages) STMICROELECTRONICS

33 / 151 page

Figure 16. OC detection strategies for H-Bridge: (left) one shunt resistor for LS, DSM for HS; (center) two shunt

resistors; (right) DSM

GND

Rshunt

GND

VBR

Rshunt

GND

VBR

Rshunt

GADG2802170759PS

CH1_OC

Out1(HB+)

CH3_OC

CH3

CH1

CH2_OC

VBR

Out2(HB-)

CH2

CH4

CH4_OC

CH1_OC

Out1(HB+)

CH3_OC

CH3

CH1

CH2_OC

Out2(HB-)

CH4_OC

CH4

CH2

CH1_OC

Out1(HB+)

CH3_OC

CH3

CH1

CH2_OC

Out2(HB-)

CH4_OC

CH4

CH2

When shunt measurement is selected, current limitation feature is available.

•

In case current limitation feature is enabled (HBx_ILIM_en = 1), the comparator on CH3/CH7 is used for

current limitation while the one on CH4/CH8 detects OC. In order to guarantee full protection of the load and

the FETs, CH4/CH8 overcurrent comparator is enabled even if transistor is OFF phase. Therefore, in case

Rshunt is shorted to battery, the OC event will be immediately detected;

•

In case current limitation feature is disabled (HBx_ILIM_en = 0), both LS channels are used for OC

detection. OC comparators are active only in the ON phase of the transistors.

OC detection timings depend on the selected sensing strategy, as explained in Section 6.3.3 OC sensing

strategy. Once an actual OC event has been recognized, behavior depends on the current limitation feature:

•

If HBx_ILIM_en = 0, the current limitation feature is disabled and the H-Bridge is three-stated (all FETs

actively OFF, load floating);

•

If HBx_ILIM_en = 1, the current limitation feature is enabled. The device will limit the current one more time

after OC threshold crossing and, in case of failure still persisting, the H-Bridge is three-stated (all FETs

actively OFF, load floating) after tOC + tOFF (refer to Figure 18).

5.5.6

Current limitation for H-Bridge

Current limitation feature is able to limit the maximum current in the load modulating the NPWM signal, as shown

in Figure 17. This allows keeping the current of the load below the current limitation threshold (ILIM_th). Current

limitation function is available only when shunt measurement is selected and can be activated setting

HBx_ILIM_en = 1.

Current limitation threshold (I LIM_th) is set by OC_config_03 [5-0] bit for H-bridge 1 and OC_config_07 [5-0] bit

for H-Bridge 2. Hence, channel 3 is no longer used for OC detection in H-Bridge 1, but it activates the current

limitation. The same function is implemented on channel 7 in H-Bridge 2.

L9945

H-Bridge

DS12275 - Rev 8

page 33/151

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