ISL6308CRZ Intersil, ISL6308CRZ Datasheet - Page 21

• Manufacturer Part Number: ISL6308CRZ
• Description: IC CTRLR PWM 3PHASE BUCK 40-QFN
• Manufacturer: Intersil

Specifications of ISL6308CRZ

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 66.6%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

After choosing a new value for R
necessary to adjust the value of R
load droop voltage. Use Equation 26 to obtain the new value
for R
Compensation
The two opposing goals of compensating the voltage
regulator are stability and speed. Depending on whether the
regulator employs the optional load-line regulation as
described in “Load Line (Droop) Regulation” on page 13,
there are two distinct methods for achieving these goals.
Compensating the Load-Line Regulated Converter
The load-line regulated converter behaves in a similar
manner to a peak current mode controller because the two
poles at the output filter L-C resonant frequency split with the
introduction of current information into the control loop. The
final location of these poles is determined by the system
function, the gain of the current signal, and the value of the
compensation components, R
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 18.
3. Select a new value, R
4. Replace R
about L/DCR/2 (sec/div). For example, with L = 1µH and
DCR = 1mΩ, set the oscilloscope to 500µs/div.
resistor based on the original value, R
Equation 27.
the error is corrected. Repeat the procedure if necessary.
R
S
FIGURE 18. TIME CONSTANT MISMATCH BEHAVIOR
COMP 2
.
ΔV
1
,
=
COMP
R
COMP 1
with the new value and check to see that
,
COMP,2
⋅
Δ
----------
Δ
V
V
21
1
2
2
and C
COMP
, for the time constant
S
to obtain the desired full
1
, it will most likely be
.
COMP,1
ΔV
ΔI
2
, using
V
I
TRAN
(EQ. 27)
OUT
ISL6308
Since the system poles and zero are affected by the values
of the components that are meant to compensate them, the
solution to the system equation becomes fairly complicated.
Fortunately, there is a simple approximation that comes very
close to an optimal solution. Treating the system as though it
were a voltage-mode regulator, by compensating the L-C
poles and the ESR zero of the voltage mode approximation,
yields a solution that is always stable with very close to ideal
transient performance.
The feedback resistor, R
outlined in “Load Line Regulation Component Selection (DCR
Current Sensing)” on page 20. Select a target bandwidth for
the compensated system, F
large enough to assure adequate transient performance, but
smaller than one third of the per-channel switching frequency.
The values of the compensation components depend on the
relationships of F
ESR zero frequency. For each of the following three, there is a
separate set of equations for the compensation components.
Case 1:
Case 2:
FIGURE 19. COMPENSATION CONFIGURATION FOR
R
LOAD-LINE REGULATED ISL6308 CIRCUIT
R
C
---------------------------
2π
1
---------------------------
2π
R
C
2
1
2
1
0
⋅
=
=
⋅
1
to the L-C double pole frequency and the
=
=
1
L C
R
------------------------------------------------------------------------------- -
(
R
L C
2π
R
------------------------------------------------ -
2π V
⋅
1
2
⋅
1
⋅
)
⋅
C
⋅
V
--------------------------------------------------------------- -
2
1
≤
0.66 V
2π F
----------------------------------------------------------- -
2
, has already been chosen as
>
OSC
⋅
F
C
OSC
(Optional)
F
F
0
0
1
⋅
2
0
0
. The target bandwidth must be
<
0.66 V
⋅
⋅
⋅
0
-------------------------------- -
2π C ESR
0.66 V
V
0.66 V
⋅
(
⋅
IN
2π
OSC
R
V
⋅
1
⋅
COMP
OSC
VDIFF
)
⋅
⋅
2
⋅
1
f
IN
⋅
⋅
0
⋅
FB
IN
R
IN
F
⋅
2
0
1
⋅
⋅
L C
L C
⋅
L C
⋅
⋅
ISL6308
September 30, 2008
(EQ. 28)
FN9208.4