15/20

L6615

Figure 15. Distributed power system for +48V bus

In this application is inserted also a circuit for the square current limit protection in case of overcurrent (R1-

Q1): being the voltage at the CGA pin directly proportional to the current carried by the relevant section,

it is possible to set the CGA resistor such that, until the output current is in the right range, the CGA voltage

path, reducing the duty cycle and consequently the output voltage.

Current sharing can be required in AC to DC application like distributed power system (DPS) for telecom

applications: if the output voltage is higher than the absolute maximum rating for the current sense pins

(CS+ and CS-) high side sensing can not be performed unless adding other components; the current

sense is performed on the ground return.

introduced to translate the sense signal in the L6615 input pin common mode range.

In fig.15 two AC-DC converters supply the same load through a +48V bus; these converters usually exhibit

also a +12V auxiliary output useful to supply the L6615 whose ADJ pin works on the +48V feedback sec-

tion (COMP pin and CGA pin connections are not showed) in figure 15.

7

LOW VOLTAGE BUSES

The L6615 has a "doubled" sense structure, designed to perform both high side and low side sensing: the

first solution is usually considered more convenient. Actually low side sensing means to split the ground

return as many times as the power supplies paralleled are: on each of these paths it is then necessary to

place the sense resistor introducing a drop between the power supply ground and the common load neg-

ative reference.

The voltage at CS+ pin is read by an internal comparator and compared with a reference corresponding

parator triggers the High Side Amplifier (HSA); being the threshold provided by hysteresis, then the Low

Side Amplifier (LSA) will be triggered as VCS+ is lower than 1.44V (typ.).

erating range of HSA; usually LSA is operating when the sense resistor is placed on the ground return,

between the negative load terminal and the negative power supply output (fig 10.b) and HSA when the

sense resistor is placed between the power supply positive output and the load.

threshold (or even lower) exploiting the low sense internal structure (LSA).

L

O

A

D

+48V

+48V

SH bus

+12V

+12V

SH

Vcc

CS-

CS+

Vcc

CS-

CS+

SH

L6615

R

G

R

G

R

G

R

G

R

SNS

R

SNS

AC

Mains

AC

Mains

AC

Mains

+48V GND

+48V GND

DPS1

DPS2

ADJ

ADJ

+48V (*)

feedback

+48V (*)

feedback

I

OUT1

I

OUT2

GND

GND

L6615

(*) the center of the

output feedback divider

is usually connected to

a

voltage

compatible

with L6615 AMR