L6615 STMicroelectronics, L6615 Datasheet - Page 9

• Manufacturer Part Number: L6615
• Description: High/low side load share controller
• Manufacturer: STMicroelectronics

2
A sense resistor is typically used to generate the voltage drop, proportional to the load current, measured
by the CSA (Current Sense Amplifier), whose input pins (pins #2 and #3) are connected across of R
through two identical resistors (RG1 and RG2).
The CSA consists of 2 sections (see fig. 10), one responsible for the high side sensing, the other for low
side sensing. An internal comparator activates the relevant section in accordance with the voltage present
at CS+ pin: if this voltage is higher than 1.6V (typ), then the high side sensing section will be activated
(fig10.a) otherwise the low side sensing one will (fig 10.b). For the sake of simplicity we will consider R
R
As the voltage drop I
the controlled current mirror to:
– sink current from the CS+ pin in case of high side sensing (neglecting input bias current, no current flows
– source current from the CS- pin in case of low side sensing (neglecting input bias current, no current
The local feedback imposes the same voltage at the current sense input pins, so under closed loop con-
dition V
The current
(IC
ing a drop across the R
Only the L6615 V
at the current sense pins.
In noisy applications, two capacitors of small value (e.g. 1nF) connected between current sense pins and
ground could be useful to clean the signal at the input of the current sense amplifier.
For low voltage buses application, see paragraph 7.
Figure 10. Current sense section
G2
through CS- pin);
flows through CS- pin).
R
R
S+
SENSE
SENSE
I
I
OUT
OUT
= R
LOAD(+)
LOAD(+)
CURRENT SENSE SECTION
PS+
PS+
in case of high side, I
G
SENSE
.
V
V
R
R
V
V
SENSE
SENSE
R
R
G
G
RG
RG
G
G
=VR
CS+
CS+
CS-
CS-
CC
G
a) high side sensing
.
limits the upper voltage at the CGA and SH pin, independently of the voltage present
OUT
1.6V
1.6V
CGA
*R
+
+
-
-
+
+
-
-
LSA
LSA
HSA
HSA
COMPARE
COMPARE
CS-
SENSE
external resistor: two internal buffers transfer V
I
I
CS+
CS+
in case of low side) is then internally mirrored and sent to the CGA pin caus-
CONTROLLED
CONTROLLED
SINK
SINK
CURRENT
CURRENT
is present at the input of the Sense Amplifier section, its output forces
MIRROR
MIRROR
1:1
1:1
CSA
CSA
V
L6615
L6615
SH
I
CS
CGA
CGA
R
R
I
I
=
CGA
CGA
CGA
CGA
=
I
-------------------------------------- -
OUT
V
-------------- R
R
SNS
G
R
R
LOAD(-) / GND
LOAD(-) / GND
G
R
R
S ENSE
I
I
SENSE
SENSE
OUT
OUT
CGA
PS-
PS-
V
V
V
V
R
R
SENSE
SENSE
RG
RG
R
R
G
G
G
G
CS+
CS+
CS-
CS-
b) low side sensing
CGA
1.6V
1.6V
+
+
-
-
-
-
+
+
signal on the share pin so:
HSA
HSA
LSA
LSA
COMPARE
COMPARE
I
I
CS-
CS-
SOURCE
SOURCE
CONTROLLED
CONTROLLED
CURRENT
CURRENT
MIRROR
MIRROR
1:1
1:1
CSA
CSA
L6615
L6615
L6615
CGA
CGA
SENSE
I
I
R
R
CGA
CGA
CGA
CGA
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G1
=