参数资料
型号: ISL6263CEVAL1
厂商: Intersil
文件页数: 14/18页
文件大小: 0K
描述: EVAL BOARD 1 FOR ISL6263C
标准包装: 1
系列: *
ISL6263C
VDD
OCP
?
+
10μA
+
I SENSE
?
OCSET
ISP
ISN
R OCSET
R S
+
ICOMP
+
?
VO
V N
-
V DCR
FIGURE 8. EQUIVALENT MODEL OF CURRENT SENSE USING INDUCTOR DCR CURRENT SENSE
and the switching frequency in CCM is approximated using
Equation 6:
Sensing the time varying inductor current accurately
requires that the parallel R-C network time constant match
( t – 0.5 × 10
)
– 6
– 12
R FSET = ---------------------------------------
400 × 10
(EQ. 6)
the inductor L/DCR time constant. Equation 10 shows this
relationship:
------------- = ? ? ? C N
L ? R N ( T ) ? R S ?
? R N ( T ) + R S ?
DCR
(EQ. 7)
( 3.33 × 10
– 0.5 × 10
)
7.1 × 10 = --------------------------------------------------------------------
400 × 10
? ------------- ?
? R N ( T ) ? R S ?
? R N ( T ) + R S ?
t is the switching period. For example, the value of R FSET for
300kHz operation is approximated using Equation 7:
– 6 – 6
3
– 12
This relationship only applies to operation in constant
conduction mode because the PWM frequency naturally
decreases as the load decreases while in diode emulation
-------------------------------
Solution of C N yields:
L
? DCR ?
C N = -------------------------------------
? ------------------------------- ?
(EQ. 10)
(EQ. 11)
G 1 ( T ) = -------------------------------
R N ( T ) + R S
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 O
generates a DC voltage drop on the inductor DCR.
Equation 8 gives this relationship:
The first step is to adjust R N (T) and R S such that the correct
current information appears between the ISP and VO pins
even at light loads. Assume V N is the voltage drop across
R N (T). The V N to V DCR gain G 1 (T) provides a reasonable
amount of light load signal from which to derive the current
information. G 1 (T) is given by Equation 12:
R N ( T )
(EQ. 12)
The gain of the current sense amplifier circuit is expressed in
Equation 13:
R IS1
V DCR = I O ? DCR
(EQ. 8)
R IS2
K ISENSE = 1 + -------------
(EQ. 13)
An R-C network senses the voltage across the inductor to
V ICOMP = V O + V N ? K ISENSE
get the inductor current information. R N represents the
equivalent resistance of R P and the optional NTC network
consisting of R NTC and R NTCS . R N is temperature T
dependent and is given by Equation 9:
The current sense amplifier output voltage is given by
Equation 14:
(EQ. 14)
R N ( T ) = ------------------------------------------------------------
( R NTC + R NTCS ) ? R P
R NTC + R NTCS + R P
(EQ. 9)
The inductor DCR is a function of temperature T and is
approximated using Equation 15:
If the NTC network is not used, simply set R N (T) = R P .
14
DCR ( T ) = DCR ( +25 ° C ) ? ( 1 + 0.00393 ? T – ( +25 ° C ) )
(EQ. 15)
FN6745.1
July 8, 2010
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