STMicroelectronics L6227 DMOS Evaluation Board EVAL6227PD EVAL6227PD Hoja De Datos

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DocID9453 Rev 2

The L6227 device includes a constant off time PWM current controller for each of the two 
bridges. The current control circuit senses the bridge current by sensing the voltage drop 
across an external sense resistor connected between the source of the two lower power 
MOS transistors and ground, as shown in 

. As the current in the load builds up the 

voltage across the sense resistor increases proportionally. When the voltage drop across 
the sense resistor becomes greater than the voltage at the reference input (VREF

A

 or 

VREF

B

), the sense comparator triggers the monostable switching the low-side MOS off. The 

low-side MOS remains off for the time set by the monostable and the motor current 
recirculates in the upper path. When the monostable times out the bridge will again turn on. 
Since the internal deadtime, used to prevent cross conduction in the bridge, delays the turn 
on of the power MOS, the effective off time is the sum of the monostable time plus the 
deadtime. 

 shows the typical operating waveforms of the output current, the voltage drop 

across the sensing resistor, the RC pin voltage and the status of the bridge. Immediately 
after the low-side power MOS turns on, a high peak current flows through the sensing 
resistor due to the reverse recovery of the freewheeling diodes. The L6227 device provides 
a 1 

s blanking time t

BLANK

 that inhibits the comparator output so that this current spike 

cannot prematurely retrigger the monostable.

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