LX1671CLQ-TR Просмотр технического описания (PDF) - Microsemi Corporation
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LX1671CLQ-TR Datasheet PDF : 21 Pages
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LX1671
TM
®
Multiple Output LoadSHARE™ PWM
PRODUCTION DATA SHEET
THEORY OF OPERATION (CONTINUED)
BI-PHASE, LOADSHARE (PROPORTIONAL METHOD)
The best topology for generating a current ratio at full load
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.
Also a speed up capacitor can be used between the offset
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.
The use of a MOSFET input amplifier is required for the buffer
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.
L1,
Switch
Side
62k LPF1
4700pF
L2,
Switch
Side
62k
LPF2
Ra
4700pF
Offset Amp
Rin
-
-
Rf
Phase 2
Error Amp PWM
Input
RF2
-
FB2
62k
Vos
+5V @ 7W
1.5V
+46.7mV
V1
ESR L1
10mΩ
Phase 1
Offset
-
Voltage
Generator
+
1.5V
V2
+73.3mV
ESR L2
10mΩ
Phase 2
1M Rb
+3.3V @ 11W
4.67A
7.33A
Vou
1.5V @ 12A
18W
Figure 9 – LoadSHARE Using Proportional Control
Copyright © 2000
Rev. 1.2b, 2006-02-13
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 14
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