isl6263c Intersil Corporation, isl6263c Datasheet - Page 14

• Manufacturer Part Number: isl6263c
• Description: 5-bit Vid Single-phase Voltage Regulator With Current Monitor For Gpu Core Power
• Manufacturer: Intersil Corporation

and the switching frequency in CCM is approximated using
Equation 6:
t is the switching period. For example, the value of R
300kHz operation is approximated using Equation 7:
This relationship only applies to operation in constant
conduction mode because the PWM frequency naturally
decreases as the load decreases while in diode emulation
mode.
Inductor DCR Current Sense
ISL6263C provides the option of using the inductor DCR for
current sense. To maintain the current sense accuracy, an
NTC compensation network is optional when using DCR
sense. The process to compensate the DCR resistance
variation takes several iterative steps. Figure 2 shows the
DCR sense method. Figure 8 shows the simplified model of
the current sense circuitry. The inductor DC current I
generates a DC voltage drop on the inductor DCR.
Equation 8 gives this relationship:
An R-C network senses the voltage across the inductor to
get the inductor current information. R
equivalent resistance of R
consisting of R
dependent and is given by Equation 9:
If the NTC network is not used, simply set R
V
R
7.1
R
DCR
N
FSET
T ( )
×10
=
3
=
=
I
=
(
----------------------------------------------------------- -
O
R
R
(
---------------------------------------
(
--------------------------------------------------------------------
NTC
⋅
NTC
t 0.5
400
3.33
DCR
–
NTC
+
×
+
×
R
×
400
10
R
10
FIGURE 8. EQUIVALENT MODEL OF CURRENT SENSE USING INDUCTOR DCR CURRENT SENSE
NTCS
10
NTCS
and R
–
–
12
–
6
×
6
–
10
)
0.5
) R
+
–
NTCS
⋅
P
12
R
×
P
and the optional NTC network
P
14
10
. R
–
6
OCP
)
N
is temperature T
−
+
+
−
N
represents the
10µA
N
(T) = R
I
SENSE
↓
−
+
FSET
O
P
OCSET
(EQ. 7)
(EQ. 8)
ICOMP
(EQ. 6)
.
(EQ. 9)
VDD
VO
ISN
for
ISL6263C
ISP
R
OCSET
Sensing the time varying inductor current accurately
requires that the parallel R-C network time constant match
the inductor L/DCR time constant. Equation 10 shows this
relationship:
Solution of C
The first step is to adjust R
current information appears between the ISP and VO pins
even at light loads. Assume V
R
amount of light load signal from which to derive the current
information. G
The gain of the current sense amplifier circuit is expressed in
Equation 13:
The current sense amplifier output voltage is given by
Equation 14:
The inductor DCR is a function of temperature T and is
approximated using Equation 15:
-------------
DCR
C
G
K
V
DCR T ( )
N
ISENSE
N
1
ICOMP
L
T ( )
(T). The V
=
=
------------------------------------ -
⎛
⎜
⎝
=
------------------------------ -
R
R
⎛
⎜
⎝
N
-------------------------------
R
N
-------------------------------
R
⎛
⎝
R
=
=
=
T ( )
-------------
DCR
T ( ) R
N
N
N
R
V
DCR +25°C
L
1
T ( )
T ( )
T ( ) R
O
N
N
N
+
+
⋅
1
T ( )
+
⎞
⎠
yields:
R
R
------------ -
R
to V
(T) is given by Equation 12:
+
+
⋅
S
V
(
S
IS2
IS1
R
R
N
⎞
⎟
⎠
S
S
S
DCR
⋅
⎞
⎟
⎠
V
K
+
-
⋅
N
ISENSE
C
R
S
N
)
gain G
⋅
(
N
1
(T) and R
+
N
0.00393 T
1
V
is the voltage drop across
(T) provides a reasonable
DCR
S
⋅
such that the correct
–
(
+25°C
)
)
July 31, 2008
(EQ. 14)
(EQ. 10)
(EQ. 13)
(EQ. 11)
(EQ. 12)
(EQ. 15)
FN6745.0