ISL6316 Intersil Corporation, ISL6316 Datasheet - Page 14

• Manufacturer Part Number: ISL6316
• Description: Enhanced 4-Phase PWM Controller
• Manufacturer: Intersil Corporation

With the internal low-offset current amplifier, the capacitor
voltage V
Therefore the current out of ISEN+ pin, I
to the inductor current.
Equation 5 shows that the ratio of the channel current to the
sensed current I
resistor and the DCR of the inductor.
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense
resistor R
as the current sense element (see Figure 5). This technique is
more accurate, but reduces overall converter efficiency due to
the additional power loss on the current sense element
R
Equation 6 shows the ratio of the channel current to the
sensed current I
MOSFET R
The controller can also sense the channel load current by
sampling the voltage across the lower MOSFET R
(see Figure 6). The amplifier is ground-reference by
connecting the ISEN- pin to the source of the lower MOSFET.
ISEN+ pin is connected to the PHASE node through the
current sense resistor R
equivalent to the voltage drop across the R
lower MOSFET while it is conducting. The resulting current
out of the ISEN+ pin is proportional to the channel current I
I
I
SEN
SEN
SENSE
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FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
=
=
ISL6316 INTERNAL CIRCUIT
I
I
.
L
L
C
SENSE
SAMPLE
⋅
⋅
I
HOLD
is replicated across the sense resistor R
----------------- -
R
R
-----------------------
SEN
DS(ON)
DCR
R
ISEN
SENSE
&
I
n
ISEN
SEN
SEN
=
in series with each output inductor can serve
I
L
SENSING
.
R
------------------------- -
is driven by the value of the sense
R
SENSE
ISEN
ISEN
+
-
. The voltage across R
14
ISEN-(n)
ISEN+(n)
L
R
SEN
I
SENSE
L
DS(ON)
, is proportional
R
ISEN(n)
C
V
OUT
OUT
DS(ON)
of the
ISEN
ISEN
(EQ. 5)
(EQ. 6)
.
is
L.
ISL6316
Equation 7 shows the ratio of the channel current to the
sensed current I
Both inductor DCR and MOSFET R
as the temperature increases. Therefore the sensed current
will increase as the temperature of the current sense element
increases. In order to compensate the temperature effect on
the sensed current signal, a Positive Temperature Coefficient
(PTC) resistor can be selected for the sense resistor R
or the integrated temperature compensation function of
ISL6316 should be utilized. The integrated temperature
compensation function is described in the Temperature
Compensation section.
Channel-Current Balance
The sensed current I
together and divided by the number of active channels. The
resulting average current I
load current. Channel current balance is achieved by
comparing the sampled current of each channel to the
average current to make an appropriate adjustment to the
WPM duty cycle of each channel. Intersil’s patented current-
balance method is illustrated in Figure 7. In the figure, the
average current combines with the channel 1 current I
create an error signal I
the pulse width commanded by V
unbalance and force I
error signal correction is applied to each active channel.
I
SEN
FIGURE 6. MOSFET R
ISL6316 INTERNAL CIRCUIT
SAMPLE
HOLD
=
&
I
n
I
I
L
SEN
R
------------------------ -
R
DS ON
ISEN
=
(
I
SEN
L
R DS ON
--------------------------- -
+
)
-
R
.
n
ISEN
ER
(
from each active channel are summed
ER
DS(ON)
toward zero. The same method for
. The filtered error signal modifies
AVG
)
ISEN-(n)
ISEN+(n)
EXTERNAL CIRCUIT
CURRENT-SENSING CIRCUIT
provides a measure of the total
R
(PTC)
ISEN
COMP
DS(ON)
to correct any
V
IN
value will increase
I L xR DS ON
+
-
N-CHANNEL
MOSFETs
I
L
August 31, 2005
(
1
ISEN
FN9227.0
(EQ. 7)
)
to
,