![](http://datasheet.mmic.net.cn/370000/L6615_datasheet_16703483/L6615_15.png)
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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
is lower than V
REF
+0.7. As soon as this value is overcome, then the bipolar pushes current in the feedback
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.
To maintain high side sensing two resistor dividers (between the edge of R
SENSE
and ground) could be
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
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
to the switchover threshold V
THcs+
whose value is typically 1.6V. If such value is overcome, then the com-
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.).
Hence V
THcs+
defines the threshold between the operating range of LSA, (referring to fig.10) and the op-
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.
It is however possible to perform high side sensing for applications whose output voltage is close to V
THcs+
threshold (or even lower) exploiting the low sense internal structure (LSA).
LOW VOLTAGE BUSES
L
O
A
D
+48V
+48V
SH bus
+12V
+12V
SH
Vcc
CS-
ADJ
CS+
Vcc
CS-
ADJ
CS+
SH
L6615
R
G
R
G
R
G
R
G
R
SNS
R
SNS
Mains
AC
AC
Mains
+48V GND
+48V GND
DPS1
DPS2
+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