ISL6312IRZ Intersil, ISL6312IRZ Datasheet - Page 28

• Manufacturer Part Number: ISL6312IRZ
• Description: IC CTRLR PWM 4PHASE BUCK 48-QFN
• Manufacturer: Intersil

Specifications of ISL6312IRZ

• 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: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-VQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Inductor DCR Current Sensing Component
Selection
The ISL6312 senses each individual channel’s inductor
current by detecting the voltage across the output inductor
DCR of that channel (as described in the “Continuous
Current Sampling” on page 12). As Figure 18 illustrates, an
R-C network is required to accurately sense the inductor
DCR voltage and convert this information into a current,
which is proportional to the total output current. The time
constant of this R-C network must match the time constant
of the inductor L/DCR.
The R-C network across the inductor also sets the
overcurrent trip threshold for the regulator. Before the R-C
components can be selected, the desired overcurrent
protection level should be chosen. The minimum overcurrent
trip threshold the controller can support is dictated by the
DCR of the inductors and the number of active channels. To
calculate the minimum overcurrent trip level, I
Equation 32, where N is the number of active channels, and
DCR is the individual inductor’s DCR.
The overcurrent trip level of the ISL6312 cannot be set any
lower then the I
minimum overcurrent trip level is desired, follow the
steps below to choose the component values for the
R-C current sensing network:
I
OCP min
1. Choose an arbitrary value for C
MOSFET
DRIVER
value is 0.1µF.
,
ISL6312 INTERNAL CIRCUIT
SAMPLE
FIGURE 18. DCR SENSING CONFIGURATION
=
I
n
0.0375 N
-------------------------- -
DCR
OCP,min
UGATE(n)
LGATE(n)
I
SEN
⋅
+
-
level calculated above. If the
V
R
V
28
IN
ISEN
C
(s)
-
1
R
INDUCTOR
. The recommended
1
L
V
ISEN-(n)
ISEN+(n)
L
I
(s)
L
V
C
DCR
R
*R
-
(s)
C
2*
1
2
OCP,min
-
is OPTIONAL
C
V
OUT
(EQ. 32)
, use
OUT
ISL6312
If the desired overcurrent trip level, I
minimum overcurrent trip level, I
divider R-C circuit should be used to set the desired trip
level. Follow the steps below to choose the component
values for the resistor divider R-C current sensing
network:
Due to errors in the inductance or DCR it may be necessary
to adjust the value of R
correctly. The effects of time constant mismatch can be seen
in the form of droop overshoot or undershoot during the
initial load transient spike, as shown in Figure 19. Follow the
steps below to ensure the R-C and inductor L/DCR time
constants are matched accurately.
2. Plug the inductor L and DCR component values, and the
3. Resistor R
1. Choose an arbitrary value for C
2. Plug the inductor L and DCR component values, the
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 19.
value for C
calculate the value for R
value is 0.1μF.
value for C
channels N, and the desired overcurrent protection level
I
R
about L/DCR/2 (sec/div). For example, with L = 1μH and
DCR = 1mΩ, set the oscilloscope to 500μs/div.
R
R
R
OCP
FIGURE 19. TIME CONSTANT MISMATCH BEHAVIOR
1
1
1
2
ΔV
and R
=
=
=
1
into Equations 34 and 35 to calculate the values for
-------------------------
DCR C
-------------------------------------- -
C
--------------------------------------------------------------------------------- -
C
1
1
L I
⋅
⋅
2
L
0.0375 N
(
2
.
⋅
I
1
1
⋅
OCP
OCP
should be left unpopulated.
chosen in step 1, into Equation 33 to
chosen in step 1, the number of active
1
⋅
L I
⋅
DCR 0.0375 N
⋅
1
OCP
and R
–
1
.
2
OCP,min
to match the time constants
I
I
⋅
OCP
OCP
1
OCP
. The recommended
)
>
=
, then a resistor
, is greater then the
I
OCP min
I
OCP min
ΔV
ΔI
2
,
,
February 1, 2011
V
I
(EQ. 33)
TRAN
(EQ. 34)
(EQ. 35)
OUT
FN9289.6