ISL6564A Intersil Corporation, ISL6564A Datasheet - Page 13

• Manufacturer Part Number: ISL6564A
• Description: Multiphase PWM Controller
• Manufacturer: Intersil Corporation

Current Sensing
The ISL6564A supports inductor DCR sensing, MOSFET
r
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
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 4.
The voltage on the capacitor V
proportional to the channel current I
If the R-C network components are selected such that the
RC time constant matches the inductor L/DCR time
constant, then V
DCR.
V
DS(ON)
V
C
L
=
=
⎛
⎝
-------------------------------------------------------------------- -
I
L
s
sensing, or resistive sensing techniques. The
⋅
⋅
(
-------------
DCR
s L
FIGURE 3. SAMPLE AND HOLD TIMING
L
⋅
(
s RC
+
+
⋅
DCR
C
1
L
⎞
⎠
, flowing through the inductor, will also
is equal to the voltage drop across the
⋅
+
PWM
(
DCR I
t
)
1
HOLD
)
SWITCHING PERIOD
⋅
L
13
I
)
L
TIME
C
SAMPLE CURRENT, I
, can be shown to be
L
, see Equation 5.
I
SEN
L
.
n
(EQ. 4)
(EQ. 5)
ISL6564A
The capacitor voltage V
sense resistor R
is proportional to the inductor current. Equation 6 shows the
proportion between the channel current and the sensed
current I
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
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.
I
SEN
ISL6564A INTERNAL CIRCUIT
=
SAMPLE
HOLD
I
SEN
FIGURE 4. DCR SENSING CONFIGURATION
L
&
ISEN
I
n
I
⋅
SEN
----------------- -
R
DCR
ISL6207
, is driven by the value of the sense resistor
ISEN
.
=
ISEN
PWM(n)
I
L
----------------- -
R
DCR
. The current through the sense resistor
ISEN
C
+
-
, is then replicated across the
V
IN
ISEN-(n)
ISEN+(n)
INDUCTOR
R
L
I
L
s ( )
V
L
V
DCR
C
-
C
(s)
-
R
(PTC)
ISEN(n)
March 20, 2007
C
V
OUT
OUT
(EQ. 6)
FN6285.1