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L9945 データシート(PDF) 31 Page - STMicroelectronics |
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L9945 データシート(HTML) 31 Page - STMicroelectronics |
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31 / 151 page  Table 18. Dead time values HBx_dead_time [1] HBx_dead_time [0] Dead time (min) Dead time (typ) Dead time (max) Unit 0 0 0.5 1 1.5 µs 0 1 1 2 3 µs 1 0 3 4 5 µs 1 1 7 8 (default) 9 µs Note: x = H-bridge number The dead time intervenes in case of H-Bridge direction change, that is upon DIR transitions. The following table describes the output behavior in case of DIR transition. Table 19. Output response in case of DIR transition DIR Transition Q1/Q5 Q2/Q6 Q3/Q7 Q4/Q8 0 → 1 Turns ON after HBx_dead_time, if NPWM was ‘0’ before DIR switch and did not toggle during dead time Turns OFF immediately Turns OFF immediately Turns ON after HBx_dead_time 1 → 0 Turns OFF immediately Turns ON after HBx_dead_time, if NPWM was ‘0’ before DIR switch and did not toggle during dead time Turns ON after HBx_dead_time Turns OFF immediately Note: NPWM should be stable before applying the DIR transition, and it should not be switched during the dead-time due to DIR switch. Otherwise, once dead-time for DIR switch event has expired, the dead-time for NPWM transition will start, resulting in twice the dead-time applied. Once NPWM has been toggled at tNPWM_SWITCH time instant, DIR input shall not be switched within a defined grey-zone in respect to tNPWM_SWITCH . Grey zone is defined by: tGREY=tNPWM_SWITCH +HBx_dead_time± 5 fMAIN_CLK1 For further information refer to the AN "L9945_DIR_switching_recommendations". The dead timers also operate during NPWM switching activity. Transitions are described in the following table. Table 20. Output response in case of NPWM transition DIR = 1 DIR = 0 DIR = 1 DIR = 0 NPWM Transitio n Q1/Q5 Q2/Q6 Q3/Q7 Q4/Q8 HBx_AFW = 0 HBx_AFW = 1 HBx_AFW = 0 HBx_AFW = 1 0 → 1 Turns OFF after HBx_dead_time if NPWM is still ‘1’ Turns OFF immediately Kept OFF Turns ON after 2*HBx_dead_time if NPWM is still ‘1’ Kept OFF Turns ON after 2*HBx_dead_time if NPWM is still ‘1’ 1 → 0 Turned OFF immediately. Then, it turns ON after HBx_dead_time if NPWM is still ‘0’ Turns ON after HBx_dead_time if NPWM is still ‘0’ Kept OFF Turned OFF immediately Kept OFF Turned OFF immediately Note: in case NPWM is switched with a very high frequency, which is incompatible with HBx_dead_time, the HS will be kept OFF. This happens because every time NPWM toggles 1 → 0, the HS output is reset to its default value of ‘0’. However, this condition should be avoided by choosing switching frequency and duty-cycle in order to allow dead-timer to expire after both transitions. L9945 H-Bridge DS12275 - Rev 8 page 31/151 |
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