L6917 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6917' PDF : 33 Pages View PDF
L6917B
voltage, during the removal it is discharged only by the output voltage. The following expressions give approx-
imate response time for ∆I load transient in case of enough fast compensation network response:
tapplication = -V----I-N---L--–---⋅--V-∆---O-I---U----T--
tremoval = V-L----O-⋅---U∆----TI-
The worst condition depends on the input voltage available and the output voltage selected. Anyway the worst
case is the response time after removal of the load with the minimum output voltage programmed and the max-
imum input voltage available.
Figure 9. Inductor ripple current vs Vout
9
8
7
6
5
4
3
2
1
0
0.5
L=1.5µH, Vin=12V
L=2µH,
Vin=12V
L=3µH,
Vin=12V
L=1.5µH,
Vin=5V
L=2µH,
Vin=5V
L=3µH, Vin=5V
1.5
2.5
3.5
Output Voltage [V]
MAIN CONTROL LOOP
The L6917B control loop is composed by the Current Sharing control loop and the Average Current Mode con-
trol loop. Each loop gives, with a proper gain, the correction to the PWM in order to minimize the error in its
regulation: the Current Sharing control loop equalize the currents in the inductors while the Average Current
Mode control loop fixes the output voltage equal to the reference programmed by VID. Figure 10 reports the
block diagram of the main control loop.
Figure 10. Main Control Loop Diagram
L1
+
PWM1
IINFO2
1/5
CURRENT
SHARING
DUTY CYCLE IINFO1
1/5
CORRECTION
L2
+
PWM2
ERROR
AMPLIFIER
REFERENCE
CO
RO
4/5
+
PROGRAMMED
BY VID
-
COMP
FB
D02IN1392
ZF(S)
ZFB
16/33
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