isl6306 Intersil Corporation, isl6306 Datasheet - Page 15

• Manufacturer Part Number: isl6306
• Description: 4-phase Pwm Controller With 8-bit Dac Code Capable Of Precision Rds On Or Dcr Differential Current Sensing
• Manufacturer: Intersil Corporation

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
serve 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
across R
r
resulting current out of the ISEN+ pin is proportional to the
channel current I
I
I
DS(ON)
SEN
SEN
FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
=
=
ISL6306 INTERNAL CIRCUIT
I
I
of the lower MOSFET while it is conducting. The
L
L
ISEN
SENSE
SAMPLE
⋅
⋅
I
HOLD
DS(ON)
SEN
----------------- -
R
R
-----------------------
DCR
R
ISEN
SENSE
I
&
n
ISEN
is equivalent to the voltage drop across the
=
SEN
SEN
L
SENSE
in series with each output inductor can
I
.
L
SENSING
R
------------------------- -
.
is driven by the value of the sense
R
SENSE
ISEN
.
+
-
15
ISEN-(n)
ISEN+(n)
L
ISEN
R
I L
SENSE
. The voltage
R
ISEN(n)
C
V
OUT
OUT
DS(ON)
(EQ. 5)
(EQ. 6)
ISL6306
Equation 7 shows the ratio of the channel current to the sensed current I
Both inductor DCR and MOSFET r
increase 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
temperature compensation function of ISL6306 should be
utilized. The integrated temperature compensation function
is described in the Temperature Compensation section.
Channel-Current Balance
The sensed current I
summed together and divided by the number of active
channels. The resulting average current I
measure of the total 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
signal modifies the pulse width commanded by V
correct any unbalance and force I
method for error signal correction is applied to each active
channel.
I
SEN
FIGURE 6. MOSFET
ISL6306 INTERNAL CIRCUIT
SAMPLE
HOLD
=
&
I
n
I
1
I
L
SEN
to create an error signal I
R
------------------------ -
R
DS ON
ISEN
=
(
I
SEN
L
.
R DS ON
--------------------------- -
+
)
-
R
ISEN
N
(
r
DS(ON)
from each active channel are
)
ISEN-(n)
ISEN+(n)
CURRENT-SENSING CIRCUIT
EXTERNAL CIRCUIT
R
(PTC)
ISEN
ISEN
ER
DS(ON)
ER
toward zero. The same
, or the integrated
. The filtered error
V
AVG
IN
value will
I
+
-
L
x
provides a
R
N-CHANNEL
MOSFETs
December 8, 2006
DS ON
I
L
COMP
(
FN9226.1
(EQ. 7)
)
to