lx1672 Microsemi Corporation, lx1672 Datasheet - Page 13

• Manufacturer Part Number: lx1672
• Description: Multiple Output Loadshare Pwm
• Manufacturer: Microsemi Corporation

Copyright © 2000
Rev. 1.0, 2005-08-10
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.
B
I
-P
The best topology for generating a current ratio at full load and
HASE
Switch
Switch
Side
L2,
Side
TM
L1,
, L
OAD
SHARE™ ( P
Ra
62k
4700pF
62k
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
4700pF
LPF1
LPF2
ROPORTIONAL
T H E O R Y O F O P E R A T I O N
-
RF2
Figure 9 –LoadSHARE™ Using Proportional Control
62k
FB2
M
ETHOD
Rin
Integrated Products Division
-
)
Phase 2
Error Amp
1M
®
Microsemi
Rb
-
Offset Amp
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.
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.
Rf
Also a speed up capacitor can be used between the offset
The use of a MOSFET input amplifier is required for the buffer
PWM
Input
Multiple Output LoadSHARE™ PWM
( C O N T I N U E D )
Vos
Generator
P
RODUCTION
Voltage
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
The gain of the offset
4.67A
7.33A
LX1672
1.5V @ 12A
Page 13
Vout
18W