STMicroelectronics L6227 DMOS Evaluation Board EVAL6227PD EVAL6227PD Fiche De Données

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DocID9453 Rev 2

 shows the operation of the bridge in the slow decay mode. At the start of the off 

time, the lower power MOS is switched off and the current recirculates around the upper half 
of the bridge. Since the voltage across the coil is low, the current decays slowly. After the 
deadtime the upper power MOS is operated in the synchronous rectification mode. When 
the monostable times out, the lower power MOS is turned on again after some delay set by 
the deadtime to prevent cross conduction. 

The L6227 integrates an “Overcurrent Detection” circuit (OCD). This circuit provides 
protection against a short-circuit to ground or between two phases of the bridge. With this 
internal overcurrent detection, the external current sense resistor normally used and its 
associated power dissipation are eliminated. 

 shows a simplified schematic of the 

overcurrent detection circuit.

To implement the overcurrent detection, a sensing element that delivers a small but precise 
fraction of the output current is implemented with each high-side power MOS. Since this 
current is a small fraction of the output current there is very little additional power 
dissipation. This current is compared with an internal reference current I

REF

. When the 

output current in one bridge reaches the detection threshold (typically 2.8 A) the relative 
OCD comparator signals a fault condition. When a fault condition is detected, the EN pin is 
pulled below the turn off threshold (1.3 V typical) by an internal open drain MOS with a pull 
down capability of 4 mA. By using an external R-C on the EN pin, the off time before 
recovering normal operation can be easily programmed by means of the accurate 
thresholds of the logic inputs.

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