isl6312a Intersil Corporation, isl6312a Datasheet - Page 12

• Manufacturer Part Number: isl6312a
• Description: Four-phase Buck Pwm Controller With Integrated Mosfet Drivers For Intel Vr10, Vr11, And Amd Applications
• Manufacturer: Intersil Corporation

demand on the converter during each switching cycle.
Channel-current balance is achieved by comparing the
sampled current of each channel to the cycle average
current, and making the proper adjustment to each channel
pulse width based on the error. Intersil’s patented current-
balance method is illustrated in Figure 3, with error
correction for Channel 1 represented. In the figure, the cycle
average current, I
sample, I
The filtered error signal modifies the pulse width
commanded by V
I
correction is applied to each active channel.
Continuous Current Sampling
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.
ER
NOTE: Channel 3 and 4 are optional.
V
COMP
FIGURE 3. CHANNEL-1 PWM FUNCTION AND CURRENT-
toward zero. The same method for error signal
FILTER
FIGURE 4. CONTINUOUS CURRENT SAMPLING
1
, to create an error signal I
+
I
ER
BALANCE ADJUSTMENT
-
+
f(s)
I
1
COMP
L
AVG
-
. This sensed current, I
I
AVG
PWM
, is compared with the Channel 1
MODULATOR
WAVEFORM
to correct any unbalance and force
÷ N
SWITCHING PERIOD
RAMP
12
TIME
I
I
SEN
L
ER
Σ
+
-
.
PWM1
SEN
I
, is simply a
I
I
4
3
2
CONTROL
TO GATE
LOGIC
ISL6312A
ISL6312A
The ISL6312A supports inductor DCR current sensing to
continuously sense each channel’s current for
channel-current balance. The internal circuitry, shown in
Figure 5 represents Channel N of an N-channel converter.
This circuitry is repeated for each channel in the converter,
but may not be active depending on how many channels are
operating.
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 5. The channel current
I
Equation 3 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 5. The voltage
across the sense capacitor, V
proportional to the channel current I
In some cases it may be necessary to use a resistor divider
R-C network to sense the current through the inductor. This
can be accomplished by placing a second resistor, R
across the sense capacitor. In these cases the voltage
across the sense capacitor, V
channel current I
L
V
V
, flowing through the inductor, passes through the DCR.
L
MOSFET
C
DRIVER
FIGURE 5. INDUCTOR DCR CURRENT SENSING
s ( )
s ( )
ISL6312A INTERNAL CIRCUIT
SAMPLE
=
=
I
------------------------------------- - DCR I
(
I
L
n
s R
⎛
⎝
⋅
⋅
-------------
DCR
(
s L
s L
CONFIGURATION
⋅
1
⋅
UGATE(n)
LGATE(n)
I
SEN
⋅
C
L
+
+
, and the resistor divider ratio, K.
DCR
1
+
⎞
⎠
+
1
-
)
⋅
)
V
R
V
IN
ISEN
C
⋅
C
C
(s) -
L
, becomes proportional to the
, can be shown to be
INDUCTOR
R
L
1
L
V
, shown in Equation 4.
ISEN-(n)
ISEN+(n)
L
I
(s)
L
V
C
DCR
R
*R
-
(s)
C
2*
1
2
1
-
is OPTIONAL
and C)
August 1, 2007
C
V
OUT
OUT
2
L
FN9290.3
(EQ. 3)
(EQ. 4)
,
,