isl62883c Intersil Corporation, isl62883c Datasheet - Page 18

• Manufacturer Part Number: isl62883c
• Description: Multiphase Pwm Regulator For Imvp-6.5? Mobile Cpus And Gpus
• Manufacturer: Intersil Corporation

Phase Current Balancing
The ISL62883C monitors individual phase average
current by monitoring the ISEN1, ISEN2, and ISEN3
voltages. Figure 13 shows the current balancing circuit
recommended for ISL62883C. Each phase node
voltage is averaged by a low-pass filter consisting of R
and C
R
order to eliminate the effect of phase node parasitic
PCB DCR. Equations 5 thru 7 give the ISEN pin
voltages:
where R
R
inductor output side pad and the output voltage rail;
and I
The ISL62883C will adjust the phase pulse-width
relative to the other phases to make
V
I
and R
Using same components for L1, L2 and L3 will provide
a good match of R
will determine R
recommended to have symmetrical layout for the
power delivery path between each inductor and the
output voltage rail, such that R
L1
s
V
pcb2
ISEN1
V
V
INTERNAL
ISEN1
ISEN2
ISEN3
should be routed to inductor phase-node pad in
= I
TO IC
L1
FIGURE 13. CURRENT BALANCING CIRCUIT
s
pcb1
ISEN3
ISEN2
ISEN1
and R
, and presented to the corresponding ISEN pin.
L2
, I
= V
dcr1
=
=
=
= I
L2
(
(
(
= R
R
R
R
ISEN2
, R
pcb3
dcr2
and I
dcr1
dcr3
L3
Phase3
Phase1
pcb2
Phase2
dcr2
, when there are R
+
pcb1
+
+
Cs
Cs
Cs
are parasitic PCB DCR between the
= V
R
L3
R
R
dcr1
Rs
Rs
Rs
pcb1
pcb2
pcb3
and R
= R
are inductor average currents.
, R
ISEN3
, R
)
)
)
pcb3
pcb2
×
×
×
18
dcr3
dcr2
I
I
I
L1
L2
L3
, thus to achieve
.
and R
L3
L2
L1
are inductor DCR; R
and R
pcb1
IL3
IL2
IL1
dcr1
Rdcr3
Rdcr2
Rdcr1
pcb3
dcr3
= R
= R
. It is
. Board layout
pcb2
Rpcb3
Rpcb2
Rpcb1
dcr2
= R
= R
(EQ. 5)
(EQ. 6)
(EQ. 7)
V o
pcb3
ISL62883C
pcb1
dcr3
.
s
,
Sometimes, it is difficult to implement symmetrical
layout. For the circuit shown in Figure 13, asymmetric
layout causes different R
current imbalance. Figure 14 shows a
differential-sensing current balancing circuit
recommended for ISL62883C. The current sensing
traces should be routed to the inductor pads so they
only pick up the inductor DCR voltage. Each ISEN pin
sees the average voltage of three sources: its own
phase inductor phase-node pad, and the other two
phases inductor output side pads. Equations 8 thru 10
give the ISEN pin voltages:
The ISL62883C will make V
as shown in Equations 11 and 12:
Rewriting Equation 11 gives Equation 13:
and rewriting Equation 12 gives Equation 14:
Combining Equations 13 and 14 gives:
Therefore:
FIGURE 14. DIFFERENTIAL-SENSING CURRENT
INTERNAL
V
V
V
V
V
V
V
V
R
1p
ISEN1
1p
1n
1p
2p
TO IC
ISEN2
ISEN3
dcr1
ISEN3
ISEN2
ISEN1
–
+
+
–
–
V
V
V
V
V
×
1n
2n
2p
1n
2n
I
=
=
=
L1
+
+
=
=
V
=
V
V
V
V
=
1p
1n
1n
V
BALANCING CIRCUIT
V
V
3n
3n
Cs
Cs
Cs
2p
R
2p
3p
Phase2
Phase3
Phase1
+
+
+
dcr2
V
=
=
–
V
V
–
–
2n
2p
2n
V
V
V
V
V
2n
2n
Rs
Rs
Rs
Rs
Rs
Rs
Rs
Rs
Rs
3n
×
1n
1n
+
+
+
I
V1p
V
L2
V
V
V2p
+
+
=
V3p
3n
3n
3p
V
V
V
=
2p
2n
3p
pcb1
R
+
+
–
dcr3
V
V
V
ISEN1
3n
3p
3n
, R
×
L1
L3
L2
I
pcb2
L3
IL3
IL2
IL1
= V
Rdcr1
Rdcr2
Rdcr3
and R
ISEN2
V3n
V2n
V1n
Rpcb2
Rpcb1
Rpcb3
pcb3
= V
March 18, 2010
(EQ. 10)
(EQ. 15)
(EQ. 12)
(EQ. 13)
(EQ. 14)
(EQ. 16)
(EQ. 11)
ISEN3
(EQ. 8)
thus
(EQ. 9)
FN7557.1
V o