L9945 datasheet(34/151 Pages) STMICROELECTRONICS

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Figure 17. Current limitation timing diagram

GAPG0102161535CFT

tBLANK_HB

toff

ILIM_th

(CH3/7)

OC_th

(CH4/8)

tBLANK_HB

tOC

NON1/5

(NPWM)

OC Failure

toff

HBx_ILIM

Internal

NPWM

tBLANK_HB

toc

Ch4/8

toc

Ch3/7

CH4/8

CH3/7

Running Timers

toc

toff

tBLANK_HB

Current through

Load and Rshunt

Current through

Load only

Current through

Rshunt only

If the current stays above the programmed threshold (ILIM_th) longer than tOC, the H-bridge is driven into

freewheeling phase (active freewheeling or not, depending on HBx_AFW bit) for a programmable OFF time

(tOFF). During tOFF, high-side outputs are actively OFF but low-side outputs remain controlled according to DIR

and HBx_AFW values, performing a freewheeling action on the low-side.

Once tOFF expires, load current is compared against ILIM_th threshold:

•

In case load current is below ILIM_th, normal operation can continue (refer to Figure 17).

•

In case current is not below ILIM_th, the high-side channel is turned on for a tFIL_ON + tOC period and then

turned off for another tOFF time. Such operation continues until either the current decreases below ILIM_th or

the current reaches the overcurrent threshold and H-Bridge is three-stated (all FETs actively OFF, load

floating) (refer to Figure 18).

L9945

H-Bridge

DS12275 - Rev 8

page 34/151

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