ISL6312CRZ-TK Intersil, ISL6312CRZ-TK Datasheet - Page 12

• Manufacturer Part Number: ISL6312CRZ-TK
• Description: IC CTRLR PWM 4PHASE BUCK 48-QFN
• Manufacturer: Intersil

Specifications of ISL6312CRZ-TK

• Applications: Controller, Intel VR10, VR11, AMD CPU
• Voltage - Input: 5 ~ 12 V
• Number Of Outputs: 1
• Voltage - Output: 0.38 ~ 1.6 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-VQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In order to realize the thermal advantage, it is important that
each channel in a multiphase converter be controlled to
carry equal amounts of current at any load level. To achieve
this, the currents through each channel must be sampled
every switching cycle. The sampled currents, I
active channel are summed together and divided by the
number of active channels. The resulting cycle average
current, I
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.
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
AVG
1
, to create an error signal I
+
I
, provides a measure of the total load-current
ER
BALANCE ADJUSTMENT
-
+
f(s)
I
1
COMP
AVG
-
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
I
I
I
n
4
3
2
, from each
CONTROL
TO GATE
LOGIC
ISL6312
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.
The ISL6312 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
L
V
, flowing through the inductor, passes through the DCR.
L
MOSFET
DRIVER
FIGURE 5. INDUCTOR DCR CURRENT SENSING
s ( )
ISL6312 INTERNAL CIRCUIT
SAMPLE
=
I
I
L
n
⋅
(
s L
CONFIGURATION
⋅
UGATE(n)
LGATE(n)
I
SEN
+
L
. This sensed current, I
DCR
+
-
)
V
R
V
IN
ISEN
C
C
(s)
, can be shown to be
-
INDUCTOR
R
L
1
L
V
, shown in Equation 4.
ISEN-(n)
ISEN+(n)
L
I L
(s)
V
C
DCR
SEN
R
*R
-
(s)
C
2*
1
2
1
-
is OPTIONAL
, is simply a
and C)
February 1, 2011
C
V
OUT
OUT
L
FN9289.6
(EQ. 3)
,