L9945 datasheet(30/144 Pages) STMICROELECTRONICS

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Table 18. Dead time values

HBx_dead_time [1]

HBx_dead_time [0]

Dead time (min)

Dead time (typ)

Dead time (max)

Unit

0.5

1.5

µs

8 (default)

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 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± 5fMAIN_CLK1

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

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

Functional description

DS12275 - Rev 10

page 30/144

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