L6228Q View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6228Q' PDF : 32 Pages View PDF
Circuit description
Figure 15. Area where tON can vary maintaining the PWM regulation
100
L6228Q
10
2.5μs (typ. value)
1
0.1
1
10
100
Coff [nF]
4.4
Decay modes
The CONTROL input is used to select the behavior of the bridge during the off-time. When
the CONTROL pin is low, the fast decay mode is selected and both transistors in the bridge
are switched off during the off-time. When the CONTROL pin is high, the slow decay mode
is selected and only the low-side transistor of the bridge is switched off during the off-time.
Figure 16 shows the operation of the bridge in the fast decay mode. At the start of the off-
time, both of the power MOSFETs are switched off and the current recirculates through the
two opposite free wheeling diodes. The current decays with a high dI/dt since the voltage
across the coil is essentially the power supply voltage. After the dead time, the lower power
MOSFET, in parallel with the conducting diode, is turned on in synchronous rectification
mode. In applications where the motor current is low, it is possible for the current to decay
completely to zero during the off-time. At this point, if both of the power MOSFETs were
operating in the synchronous rectification mode it would be possible for the current to build
in the opposite direction. To prevent this, the lower power MOSFET is operated in
synchronous rectification mode only. This operation is called quasi-synchronous rectification
mode. When the monostable times out, the power MOSFETs are turned on again after
some delay set by the dead time to prevent cross conduction.
Figure 17 shows the operation of the bridge in the slow decay mode. At the start of the off-
time, the lower power MOSFET 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 dead time, the upper power MOSFET is operated in the synchronous rectification mode.
When the monostable times out, the lower power MOSFET is turned on again after some
delay set by the dead time to prevent cross conduction.
16/32
Doc ID 14321 Rev 5
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