isl6333 Intersil Corporation, isl6333 Datasheet - Page 21

• Manufacturer Part Number: isl6333
• Description: Three-phase Buck Pwm Controller With Integrated Mosfet Drivers And Light Load Efficiency Enhancements For Intel Vr11.1 Applications
• Manufacturer: Intersil Corporation

Continuous Current Sensing
In order to realize proper current-balance, the currents in
each channel are sensed continuously every switching
cycle. During this time the current-sense amplifier uses the
ISEN inputs to reproduce a signal proportional to the
inductor current, I
scaled version of the inductor current.
The controllers support inductor DCR current sensing to
continuously sense each channel’s current for
channel-current balance. The internal circuitry, shown in
Figure 6 represents one channel of the controller. This
circuitry is repeated for each channel in the converter, but
may not be active depending on how many channels are
operating.
MOSFET
DRIVER
FIGURE 6. INDUCTOR DCR CURRENT SENSING
FIGURE 5. CONTINUOUS CURRENT SAMPLING
SENSE
I
n
CONFIGURATION
UGATE
LGATE
I
SEN
L
ISL6333 INTERNAL
. This sensed current, I
PWM
+
-
CIRCUIT
SWITCHING PERIOD
V
R
V
IN
C
ISEN
21
(s)
TIME
-
I
I
SEN
L
R
INDUCTOR
1
ISL6333, ISL6333A, ISL6333B, ISL6333C
L
V
RSET
ISEN-
ISEN+
L
I
(s)
L
V
R
C
DCR
SEN
SET
-
(s)
C
1
-
, is simply a
VCC
C
V
OUT
OUT
Inductor windings have a characteristic distributed
resistance or DCR (Direct Current Resistance). For
simplicity, the inductor DCR is considered as a separate
lumped quantity, as shown in Figure 6. The channel current
I
Equation 4 shows the S-domain equivalent voltage, V
across the inductor.
A simple R-C network across the inductor (R
extracts the DCR voltage, as shown in Figure 6. The voltage
across the sense capacitor, V
proportional to the channel current I
If the R
their time constant matches the inductor L/DCR time
constant, then V
DCR.
The capacitor voltage V
effective internal sense resistance, R
current through R
current. This current, I
then used by the controllers for load-line regulation,
channel-current balancing, and overcurrent detection and
limiting. Equation 6 shows that the proportion between the
channel-current, I
by the value of the effective sense resistance, R
the DCR of the inductor.
The effective internal R
current sensing process because it sets the gain of the load
line regulation loop as well as the gain of the channel-current
balance loop and the overcurrent trip level. The effective
internal R
through use of the RSET pin. Placing a single resistor, R
from the RSET pin to the VCC pin programs the effective
internal R
Output Voltage Setting
The controllers use a digital to analog converter (DAC) to
generate a reference voltage based on the logic signals at
the VID pins. The DAC decodes the logic signals into one of
the discrete voltages shown in Table 2. Each VID pin is
pulled up to an internal 1.2V voltage by a weak current
source (40µA), which decreases to 0A as the voltage at the
VID pin varies from 0 to the internal 1.2V pull-up voltage.
External pull-up resistors or active-high output stages can
augment the pull-up current sources, up to a voltage of 5V.
R
L
V
I
V
SEN
, flowing through the inductor, passes through the DCR.
ISEN
L
C
s ( )
s ( )
=
=
=
1
=
I
-C
L
I
--------- - R
400
---------------------------------------- - DCR I
(
L
ISEN
ISEN
s R
⋅
3
1
⋅
⎛
⎝
----------------- -
R
⋅
(
DCR
-------------
DCR
network components are selected such that
s L
s L
ISEN
⋅
1
⋅
⋅
resistance is user programmable and is set
resistance according to Equation 7.
⋅
SET
C
C
+
ISEN
L
+
1
is equal to the voltage drop across the
DCR
, and the sensed current, I
1
+
⎞
⎠
1
SEN
)
which is proportional to the inductor
ISEN
)
C
⋅
, is then replicated across the
, is continuously sensed and is
resistance is important to the
C
⋅
, can be shown to be
L
L
, shown in Equation 5.
ISEN
. This develops a
1
SEN
and C)
ISEN
, is driven
April 10, 2008
(EQ. 6)
, and
L
FN6520.0
(EQ. 4)
(EQ. 5)
(EQ. 7)
,
SET
,