L6229 STMicroelectronics, L6229 Datasheet - Page 9

• Manufacturer Part Number: L6229
• Description: DMOS DRIVER FOR THREE-PHASE BRUSHLESS DC MOTOR
• Manufacturer: STMicroelectronics

L6229
Figure 7. Logic Input Internal Structure
5V
ESD
PROTECTION
D01IN1329
Figure 8. Pin EN Open Collector Driving
DIAG
5V
5V
R
EN
OPEN
COLLECTOR
EN
OUTPUT
C
EN
ESD
PROTECTION
D02IN1378
Figure 9. Pin EN Push-Pull Driving
DIAG
5V
R
EN
PUSH-PULL
EN
OUTPUT
C
EN
ESD
PROTECTION
D02IN1379
3.3 PWM CURRENT CONTROL
The L6229 includes a constant off time PWM Current Controller. The current control circuit senses the bridge
current by sensing the voltage drop across an external sense resistor connected between the source of the
three lower power MOS transistors and ground, as shown in Figure 10. As the current in the motor increases
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 pin VREF the sense comparator triggers the
monostable switching the bridge off. The power MOS remain off for the time set by the monostable and the mo-
tor current recirculates around the upper half of the bridge in Slow Decay Mode as described in the next section.
When the monostable times out, the bridge will again turn on. Since the internal dead time, used to prevent
cross conduction in the bridge, delays the turn on of the power MOS, the effective Off Time t
is the sum of
OFF
the monostable time plus the dead time.
Figure 11 shows the typical operating waveforms of the output current, the voltage drop across the sensing re-
sistor, the pin RC voltage and the status of the bridge. More details regarding the Synchronous Rectification and
the output stage configuration are included in the next section.
Immediately after the Power MOS turn on, a high peak current flows through the sense resistor due to the re-
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