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AN1696 APPLICATION NOTE

of OR-ing diode (as a reference we consider the low drop Schottky diode STPS10L25D [6]).

– OR-ing FET (STS8DNF3LL)

– OR-ing DIODE (STPS10L25D)

Obviously in the case of the diode, also the sense resistor is needed: assuming the same 75mV drop, the total

dissipation will be 1.8W. We can estimate 1.4W saving, leading to about 8.5% efficiency rise.

2.2 Current sharing control

For each section one L6615 controller is associated with the few external components necessary to its opera-

tion.

Load sharing is achieved through a single wire connection (share bus) between all the paralleled modules,

whose voltage is proportional to the highest output current amongst all the active sections. In particular, being

unity the (internal) gain between CGA and SH pins, on the share bus there will be the highest of the values given

by (1).

In case of very noisy application, two capacitors (C8 and C9) allow filtering the L6615 current sense pins (#2

and #3).

The L6615 error amplifier is of transconductance type so a compensation network is required connected be-

tween L6615 pin #5 and ground; in this case an RC series network (C5-R15) determines a bandwidth of about

1KHz for the sharing loop.

The L6615 ADJ pin (pin#4) is connected to the daughter board: a current proportional to the output currents

unbalance is sunk from the feedback path of the relevant section.

The value of adjustment resistor (R13, between positive output terminal and ADJ pin) must be chosen in accor-

dance with both the maximum current sink capability of pin ADJ and the output voltage tolerance.

and the slave one could be 330mV: this is the drop that the L6615 must be able to correct imposing a current

to flow through the adjustment resistor.

Its resistance value must be lower than the feedback divider (R6 and R8) to have no impact on the value of

regulated voltage.

The design of this resistor is a very simple process: it is enough to choose for the maximum adjustment current

a value lower than the maximum specified for L6615 (8mA, worst case) and verify that this does not cause the

saturation of the L6615 internal BJT (see fig. 5) under steady state condition.

In this case:

adj. current:

min adj. resistor:

In fact this resistance value is obtained considering the parallel of R13 (motherboard) and R9 (daughter board),

each of them equal to 82

Ω.

P

DI SS

I

D

2

R

DS ON

()

0.375W

=

⋅

=

P

DIS S

0.22 I

D AVG

()

0.013 I

DR M S

()

2

1.425W

=

⋅

+

⋅

=

R

AD J m in

()

∆V

OU T M AX

()

I

AD J

----------------------------------

330mA

8mA

-------------------

41.25

Ω

==

=