lx1675 Microsemi Corporation, lx1675 Datasheet - Page 12

• Manufacturer Part Number: lx1675
• Description: Multiple Output Loadshare?? Pwm Production Data Sheet
• Manufacturer: Microsemi Corporation

Copyright © 2004
Rev. 1.2a, 2006-02-16
B
and proportional between full load and no load is shown in figure
9. The DC voltage difference between LPF1 and VOUT is a
voltage that is proportional to the current flowing in the Phase 1
inductor. This voltage can be amplified and used to offset the
voltage at LPF2 through a large impedance that will not
significantly alter the characteristics of the low pass filter. At no
load there will be no offset voltage and no offset current between
the two phases. This will give the highest efficiency at no load.
Switch
Switch
Side
I
L2,
-P
Side
The best topology for generating a current ratio at full load
L1,
HASE
TM
, L
OAD
Ra
62k
4700pF
62k
SHARE (P
4700pF
LPF1
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
LPF2
ROPORTIONAL
-
RF2
T H E O R Y O F O P E R A T I O N
62k
FB2
Figure 9 – LoadSHARE Using Proportional Control
M
ETHOD
Rin
Integrated Products Division
-
)
Phase 2
Error Amp
1M
Microsemi
®
Rb
-
Offset Amp
Rf
PWM
amplifier output and the negative input of the Phase 2 error
amplifier. This will improve the transient response of the Phase 2
output current, so that it will share more equally with phase 1
current during a transient condition.
to prevent loading the low pass filter. The gain of the offset
amplifier, and the value of Ra and Rb, will determine the ratio of
currents between the phases at full load. Two external amplifiers
are required or this method.
Input
The use of a MOSFET input amplifier is required for the buffer
Multiple Output LoadSHARE™ PWM
Also a speed up capacitor can be used between the offset
Vos
( C O N T I N U E D )
Generator
P
Voltage
RODUCTION
Offset
+46.7mV
+73.3mV
1.5V
1.5V
V
V2
1
+
-
+3.3V @ 11W
D
+5V @ 7W
ATA
Phase 1
Phase 2
ESR L1
ESR L2
10mΩ
10mΩ
S
HEET
4.67A
7.33A
LX1675
1.5V @ 12A
Page 12
Vou
18W