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ISL6316_06 Datasheet, PDF (14/29 Pages) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision rDS(ON) or DCR Differential Current Sensing for VR10 Application
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ISL6316
VIN
ISL6605
PWM(n)
IL(s)
L
DCR
INDUCTOR
VL
VC(s)
R
C
VOUT
COUT
ISL6316 INTERNAL CIRCUIT
In
RISEN(n)
(PTC)
SAMPLE
&
HOLD
+
-
ISEN
=
IL
---D----C-----R-----
RISEN
ISEN-(n)
ISEN+(n)
FIGURE 4. DCR SENSING CONFIGURATION
With the internal low-offset current amplifier, the capacitor
voltage VC is replicated across the sense resistor RISEN.
Therefore the current out of ISEN+ pin, ISEN, is proportional
to the inductor current.
Equation 5 shows that the ratio of the channel current to the
sensed current ISEN is driven by the value of the sense
resistor and the DCR of the inductor.
ISEN
=
IL
⋅
---D----C-----R-----
RISEN
(EQ. 5)
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense
resistor RSENSE in series with each output inductor can 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
RSENSE.
Equation 6 shows the ratio of the channel current to the
sensed current ISEN.
ISEN
=
IL
⋅
R-----S----E----N----S----E--
RISEN
(EQ. 6)
IL
L
RSENSE VOUT
COUT
ISL6316 INTERNAL CIRCUIT
RISEN(n)
In
SAMPLE
&
HOLD
ISEN-(n)
+
-
ISEN+(n)
ISEN
=
IL
-R----S----E-----N-----S----E---
RISEN
FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
MOSFET rDS(ON) SENSING
The controller can also sense the channel load current by
sampling the voltage across the lower MOSFET rDS(ON) (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 RISEN. The voltage across RISEN is equivalent to the
voltage drop across the rDS(ON) of the lower MOSFET while it
is conducting. The resulting current out of the ISEN+ pin is
proportional to the channel current IL.
ISEN
=
IL
-r--D-----S----(---O-----N-----)
RISEN
VIN
In
SAMPLE
&
HOLD
-
+
ISEN+(n)
RISEN
(PTC)
ISEN-(n)
IL
-
ILxrDS(ON)
+
N-CHANNEL
MOSFETs
ISL6316 INTERNAL CIRCUIT EXTERNAL CIRCUIT
FIGURE 6. MOSFET rDS(ON) CURRENT-SENSING CIRCUIT
Equation 7 shows the ratio of the channel current to the
sensed current ISEN.
ISEN
=
IL
r---D----S----(--O-----N----)
RISEN
(EQ. 7)
Both inductor DCR and MOSFET rDS(ON) value will 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 RISEN,
14
FN9227.1
December 12, 2006
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