L6615 Datasheet, PDF (9/20 Pages) STMicroelectronics – HIGH/LOW SIDE LOAD SHARE CONTROLLER

L6615
2 CURRENT SENSE SECTION
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_SENSE
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_G1=
R_G2= R_G.
As the voltage drop I_OUT*R_SENSE is present at the input of the Sense Amplifier section, its output forces
the controlled current mirror to:
– sink current from the CS+ pin in case of high side sensing (neglecting input bias current, no current flows
through CS- pin);
– source current from the CS- pin in case of low side sensing (neglecting input bias current, no current
flows through CS- pin).
The local feedback imposes the same voltage at the current sense input pins, so under closed loop con-
dition V_SENSE=VR_G.
The current
I_{C S} =
I_{--O----U----T-----}⋅_---R_{----S----E---N----S----E-}
R_G
(IC_S+ in case of high side, I_CS- in case of low side) is then internally mirrored and sent to the CGA pin caus-
ing a drop across the R_CGA external resistor: two internal buffers transfer V_CGA signal on the share pin so:
V_SH
=
V_{-----S---N----S--}
R_G
⋅
R_CGA
Only the L6615 V_CC limits the upper voltage at the CGA and SH pin, independently of the voltage present
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
PS+
R_G
I_OUT
V_RG
CS+
R_SENSE
V_SENSE
CS-
R_G
LOAD(+)
I_CS+
+
HSA
-
1.6V
COMPARE
-
LSA
+
SINK
1:1
CONTROLLED
CURRENT
MIRROR
I_CGA
CGA
R_CGA
CSA
L6615
a) high side sensing
LOAD(-) / GND
R_G
CS+
I_OUT
+
HSA
-
CSA
R_SENSE
V_SENSE
V_RG
R_G
CS-
PS-
1.6V
COMPARE
-
LSA
+
CONTROLLED
CURRENT
MIRROR
1:1
SOURCE
I_CS-
b) low side sensing
CGA
I_CGA
R_CGA
L6615
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