L9969T datasheet(20/70 Pages) STMICROELECTRONICS

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3.2.4

Power stage switching behavior

Here below (see the Table 15) the possible combinations parallel inputs/driver outputs.

Table 15. Parallel inputs combinations and output states

PWM

DIR

OUT1

OUT2

Remark

No active current flow into the load

A current flows from HS1 toward LS2

A current flows from HS2 toward LS1

Note:

HSx stands for high-side transistor of half-bridge x; LSx stands for low-side transistor of half-bridge x.

3.2.4.1

Switching sequence during regular operation

The switching sequence during a regular pulsed width modulation operation is shown in the figure below and is

made of 5 steps:

1. The connected load is powered, for example, via HSS1 and LSS2.

2. This is the transition between the powering and the active free-wheeling phase. During this short time where

HSS1 is getting non-conductive and LSS1 has not started conducting yet, a passive free-wheeling via the bulk

diode of LSS1 takes place.

3. This is the active free-wheeling. In this step LSS1 gets conductive.

4. This is the transition between the active free-wheeling and the powering phase. Similarly to the 2nd step, LSS1

is getting non-conductive and HSS1 has not started conducting yet. A passive free-wheeling via the bulk diode

of LSS1 takes place.

5. See 1st step.

Figure 11. Switching sequence during normal operation

During a regular operation, there is always one half-bridge responsible for the pulsation (in the above example the

half-bridge made of HSS1 and LSS1) and one static half-bride (in the above example the half-bridge made of

HSS2 and LSS2). As showed in the above example, the LSS of the static half-bridge remains conducting over the

complete period whereas the HSS of the static half-bridge is unused.

3.2.4.2

Switching sequence during change of direction

The switching sequence during a change of direction is shown in the figure below and is made of 5 steps:

1. The connected load is powered, for example, via HSS1 and LSS2.

2. This is the transition between the powering and the active free-wheeling phase. During this short time where

HSS1 is getting non-conductive and LSS1 has not started conducting yet, a passive free-wheeling via the bulk

diode of LSS1 takes place.

3. This is the active free-wheeling. In this step LSS1 gets conductive.

4. In this step, the change of direction is starting. Now, LSS2 is getting non-conductive but HSS2 has not started

conducting yet. The induced current resulting from the back electromotive force (back-EMF) is still flowing

from the left to the right. The current is flowing via the bulk diode of HSS2, the external capacitor and back via

LSS1.

5. In this step, HSS2 is getting conductive. The connected load is finally powered in the opposite direction via

HSS2 and LSS1.

L9969x

Functional description

DS14029 - Rev 6

page 20/70

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