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L9945TR データシート(PDF) 32 Page - STMicroelectronics |
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L9945TR データシート(HTML) 32 Page - STMicroelectronics |
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32 / 144 page  Figure 16. OC detection strategies for H-Bridge: (left) one shunt resistor for LS, DSM for HS; (center) two shunt resistors; (right) DSM M GND Rshunt M GND VBR Rshunt M GND VBR Rshunt GADG2802170759PS CH1_OC Out1(HB+) CH3_OC CH3 CH1 CH2_OC VBR Q1 Q2 Out2(HB-) CH2 Q3 Q4 CH4 CH4_OC CH1_OC Out1(HB+) CH3_OC CH3 CH1 Q3 Q1 CH2_OC Q4 Q2 Out2(HB-) CH4_OC CH4 CH2 CH1_OC Out1(HB+) CH3_OC CH3 CH1 Q3 Q1 CH2_OC Q4 Q2 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 Functional description DS12275 - Rev 10 page 32/144 |
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