L6917 STMicroelectronics, L6917 Datasheet - Page 16

• Manufacturer Part Number: L6917
• Description: 5 BIT PROGRAMMABLE DUAL-PHASE CONTROLLER
• Manufacturer: STMicroelectronics

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:
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 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
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D02IN1392
+
+
t
4/5
a pplic atio n
COMP
AMPLIFIER
PWM1
PWM2
9
8
7
6
5
4
3
2
1
0
ERROR
1/5
1/5
0.5
=
out
----------------------------- -
V
Z
IN
F(S)
+
-
L
Output Voltage [V]
1.5
–
CORRECTION
DUTY CYCLE
V
CURRENT
SHARING
PROGRAMMED
OUT
I
REFERENCE
BY VID
L=1.5 H, Vin=12V
FB
2.5
L=3 H, Vin=5V
t
Z
rem ov al
FB
I
I
INFO2
INFO1
L 1
L 2
L=2 H,
Vin=12V
L=3 H,
Vin=12V
3.5
L=1.5 H,
Vin=5V
L=2 H,
Vin=5V
C
=
O
-------------- -
V
L
OUT
I
R
O