參數(shù)資料
型號: ISL6564
廠商: Intersil Corporation
英文描述: PWM Controller with Wide Input Range 8-CDIP -55 to 125
中文描述: 多相PWM控制器,帶有線性6位DAC能精密的RDS(ON)或DCR差分電流檢測
文件頁數(shù): 13/27頁
文件大小: 798K
代理商: ISL6564
13
FN9156.2
December 27, 2004
Current Sensing
The ISL6564 supports inductor DCR sensing, MOSFET
r
DS(ON)
sensing, or resistive sensing techniques. The
internal circuitry, shown in Figures 4, 5, and 6, represents
channel n of an N-channel converter. This circuitry is
repeated for each channel in the converter, but may not be
active depending on the status of the PWM3 and PWM4
pins, as described in the
PWM Operation
section.
INDUCTOR DCR SENSING
An inductor’s winding is characteristic of a distributed
resistance as measured by the DCR (Direct Current
Resistance) parameter. Consider the inductor DCR as a
separate lumped quantity, as shown in Figure 4. The
channel current I
L
, flowing through the inductor, will also
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V
L
.
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 4.
The voltage on the capacitor V
C
, can be shown to be
proportional to the channel current I
L
, see Equation 5.
If the R-C network components are selected such that the
RC time constant matches the inductor L/DCR time
constant, then V
C
is equal to the voltage drop across the
DCR.
The capacitor voltage V
C
, is then replicated across the
sense resistor R
ISEN
. The current through the sense resistor
is proportional to the inductor current. Equation 6 shows the
proportion between the channel current and the sensed
current I
SEN
, is driven by the value of the sense resistor
chosen and the DCR of the inductor.
DCR varies with temperature, so a Positive Temperature
Coefficient (PTC) resistor should be selected for the sense
resistor R
ISEN
.
RESISTIVE SENSING
If DCR sensing is not utilized, independent current-sense
resistors in series with each output inductor can serve as the
sense element (see Figure 5). This technique is more
accurate, but reduces overall converter efficiency due to the
addition of a lossy element directly in the output path.
FIGURE 3. SAMPLE AND HOLD TIMING
TIME
PWM
I
L
SWITCHING PERIOD
I
SEN
t
HOLD
SAMPLE CURRENT, I
n
V
L
I
L
s L
DCR
+
(
)
=
(EQ. 4)
V
C
s
-------------
1
+
--------------------------------------+
DCR I
L
(
)
=
(EQ. 5)
FIGURE 4. DCR SENSING CONFIGURATION
I
n
I
SEN
I
L
R
ISEN
-----------------
=
-
+
ISEN-(n)
SAMPLE
&
HOLD
ISL6564 INTERNAL CIRCUIT
V
IN
ISEN+(n)
PWM(n)
ISL6207
R
ISEN(n)
(PTC)
DCR
L
INDUCTOR
R
V
OUT
C
OUT
-
+V
C
(s)
C
ILs
( )
-
+
V
L
I
SEN
I
L
ISEN
-----------------
=
(EQ. 6)
ISL6564
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