isl6307b Intersil Corporation, isl6307b Datasheet - Page 14

• Manufacturer Part Number: isl6307b
• Description: 6-phase Vr11 Pwm Controller With 8-bit Vid Code Capable Of Precision Rds On Or Dcr Differential Current Sensing For Applications In Which Supply Voltage Is Higher Than 5v
• 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
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
I
I
SEN
SEN
ISL6307B INTERNAL CIRCUIT
=
=
SAMPLE
HOLD
I
I
L
L
FIGURE 4. DCR SENSING CONFIGURATION
C
&
SENSE
I
n
⋅
⋅
I
SEN
----------------- -
R
R
-----------------------
is replicated across the sense resistor R
DCR
R
ISL6612
ISEN
SENSE
ISEN
=
SEN
SEN
SENSE
in series with each output inductor can
PWM(n)
I
L
-------------------
R ISEN
.
DCR
is driven by the value of the sense
.
+
-
V
IN
14
ISEN-(n)
ISEN+(n)
INDUCTOR
R
L
I
L
V
s ( )
L
SEN
V
DCR
C
-
C
(s)
, is proportional
-
R
(PTC)
ISEN(n)
C
V
ISEN
OUT
OUT
(EQ. 5)
(EQ. 6)
.
ISL6307B
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
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
I
SEN
DS(ON)
FIGURE 6. MOSFET R
ISL6307B INTERNAL CIRCUIT
FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
SAMPLE
HOLD
ISL6307B INTERNAL CIRCUIT
=
&
I
n
I
I
L
ISEN
SEN
of the lower MOSFET while it is conducting. The
SAMPLE
R
------------------------ -
I SEN
HOLD
DS(ON)
R
DS ON
I
&
n
ISEN
=
is equivalent to the voltage drop across the
(
I
=
L
SEN
L
I
R
--------------------------- -
.
+
L
)
-
R ISEN
DS ON
SENSING
R SENSE
------------------------- -
.
R ISEN
(
DS(ON)
+
-
)
ISEN-(n)
ISEN+(n)
EXTERNAL CIRCUIT
CURRENT-SENSING CIRCUIT
R
ISEN-(n)
ISEN+(n)
(PTC)
L
ISEN
DS(ON)
ISEN
R
I
SENSE
L
. The voltage
V
IN
value will
I L xR DS ON
+
-
R
ISEN(n)
C
N-CHANNEL
MOSFETs
V
OUT
OUT
I
L
DS(ON)
March 9, 2006
(
FN9225.0
(EQ. 7)
)