AN1126 Datasheet, PDF (1/16 Pages) STMicroelectronics – CURRENT SHARING OF THE L4973

AN1126
®
APPLICATION NOTE
CURRENT SHARING OF THE L4973
IN A MULTIPHASE APPLICATION
by Domenico Arrigo & Giuseppe Gattavari
INTRODUCTION
The L4973 family is a 3.5A monolithic step-down dc-dc converter, available in POWERDIP18( 12+3+3)
and SO20L (12+4+4) plastic packages. The operating input supply voltage range is from 8V to 55V, and
the output ranges from 3.3V (L4973D3.3) and 5.1V(L4973D5.1) to 40V. Other regulated outputs below
3.3V are also possible (See Application Note AN938).
Using two L4973D is possible to deliver up to 7A with a good sharing between the two sections or a re-
dundant 3.5A. The two devices work at a switching frequency of 200kHz. At Vcc = 24V, Vo = 5.1V at 7A
the efficiency is 87%. At 3.5A output, the efficiency is 90%.
Electrical Specifications
Input Voltage range
Output Voltage
Output Voltage Ripple
Output Current range
Max Output Ripple current
Min Iomax Current limit
Switching frequency
8V-30V
5.1V ±3% (Line, Load and Temperature)
47mV (0.92%/Vo)
0 to 7A
15%
8A
200kHz
Current Sharing Operating Principle
The current sharing configuration, shown in fig. 1, is based upon two L497x devices U1 and U2. Any de-
vice in the L497x family can be used for this purpose.
The U1 regulator acts as a master which regulates the output voltage.
The second section U2 works as a current follower. Its task is to deliver an output current equal to the
Figure 1. Current Sharing Operating Principle
FB
I-
L
Vcc
U1
OUT
Rs
L497x
COMP
Vcc
Cint
GND
Rint
Vout
-
+
OP-AMP
FB
Vcc
I+
L
Cout
COMP
U2
OUT
Rs
L497x
GND
May 1999
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