L6228Q View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6228Q' PDF : 32 Pages View PDF
Circuit description
L6228Q
Figure 13. Output current regulation waveforms
IOUT
VREF
RSENSE
tOFF
tON
tOFF
VSENSE
VREF
0
VRC
5V
1μs tBLANK
Slow Decay
Fast Decay
tRCRISE
1μs tBLANK
Slow Decay
Fast Decay
tRCRISE
2.5V
tRCFALL
tRCFALL
ON
OFF
SYNCHRONOUS OR QUASI
SYNCHRONOUS RECTIFICATION
B
D01IN1334
1μs tDT
C
DAB
1μs tDT
C
D
Figure 14 shows the magnitude of the off-time tOFF versus COFF and ROFF values. It can be
approximately calculated from the equations:
tRCFALL = 0.6 · ROFF · COFF
tOFF = tRCFALL + tDT = 0.6 · ROFF · COFF + tDT
where ROFF and COFF are the external component values and tDT is the internally generated
Dead Time with:
20 kΩ ≤ ROFF ≤ 100 kΩ
0.47 nF ≤ COFF ≤ 100 nF
tDT = 1 µs (typical value)
Therefore:
tOFF(MIN) = 6.6 µs
tOFF(MAX) = 6 ms
These values allow a sufficient range of tOFF to implement the drive circuit for most motors.
The capacitor value chosen for COFF also affects the rise time tRCRISE of the voltage at the
pin RCOFF. The rise time tRCRISE can be an issue if the capacitor is not completely charged
before than the next time the monostable is triggered. Therefore, the on time tON, which
depends on motors and supply parameters, has to be bigger than tRCRISE to allow a good
current regulation by the PWM stage. Furthermore, the on time tON can not be smaller than
the minimum on time tON(MIN).
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Doc ID 14321 Rev 5
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