ISL6569CRZ-T Intersil, ISL6569CRZ-T Datasheet - Page 18

• Manufacturer Part Number: ISL6569CRZ-T
• Description: IC CTRLR PWM BUCK 2PHASE 32-QFN
• Manufacturer: Intersil

Specifications of ISL6569CRZ-T

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 2MHz
• Duty Cycle: 75%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: Yes
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Frequency-max: 2MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

less than 50%. Nevertheless, both inequalities should be
evaluated, and L should be selected based on the lower of
the two results. In each equation, L is the per-channel
inductance, and C is the total output capacitance.
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 Regulation, there are two distinct
methods for achieving these goals.
COMPENSATING 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
Since the system poles and zero are effected 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 Resistor. Select a target
bandwidth for the compensated system, f
bandwidth must be large enough to assure adequate
transient performance, but smaller than 1/3 of the per-
channel switching frequency. The values of the
compensation components depend on the relationships of f
to the L-C pole frequency and the ESR zero frequency. For
FIGURE 13. COMPENSATION CONFIGURATION FOR
R
FB
LOAD-LINE REGULATED ISL6569 CIRCUIT
V
+
-
DROOP
R
C
C
FB
2
C
(OPTIONAL)
, has already been chosen as
C
18
C
and C
COMP
VDIFF
IOUT
FB
C
.
0
. The target
0
ISL6569
each of the three cases which follow, there is a separate set
of equations for the compensation components.
Case 3:
In Equations 27, L is the per-channel filter inductance
divided by 2 (the number of active channels); C is the sum
total of all output capacitors; ESR is the equivalent-series
resistance of the bulk output-filter capacitance; and V
the peak-to-peak sawtooth signal amplitude as described in
Figure 5 and Electrical Specifications.
Once selected, the compensation values in Equations 27
assure a stable converter with reasonable transient perfor-
mance. In most cases, transient performance can be
improved by making adjustments to R
value of R
oscilloscope until no further improvement is noted. Normally,
C
Equations 27 unless some performance issue is noted.
The optional capacitor C
noise away from the PWM comparator (see Figure 13). Keep
a position available for C
frequency capacitor of between 22pF and 150pF in case any
trailing edge jitter problem is noted.
Compensation without load-line regulation
The non load-line regulated converter is accurately modeled
as a voltage-mode regulator with two poles at the L-C
resonant frequency and a zero at the ESR frequency. A type-
III controller, as shown in Figure 14, provides the necessary
compensation.
Case 2:
Case 1:
C
will not need adjustment. Keep the value of C
C
while observing the transient performance on an
R
C
-------------------
2π LC
f
R
C
C
C
0
R
C
-------------------
2π LC
C
C
1
>
C
C
=
=
----------------------------- -
2πC ESR
=
=
1
R
=
=
------------------------------------------------------------ -
(
2π
R
0.75V
------------------------------------------------ -
≤
FB
2πV
2
2
R
----------------------------------- -
2πV
FB
f
(
, is sometimes needed to bypass
, and be prepared to install a high-
)
1
>
0
FB
V
--------------------------------------------
2
0.75V
<
f
PP
----------------------------------------- -
0.75 V
0
f
PP
PP
2πf
----------------------------------- -
0
IN
----------------------------- -
2πC ESR
0.75V
2
0.75 V
2π f
(
)
V
R
(
0.75V
R
2π
ESR
0
PP
FB
IN
FB
V
(
1
0
IN
)
pp
IN
2
R
V
f
f
0
0
IN
(
f
FB
pp
) C
IN
0
ESR
2
C
L
LC
)
L
LC
. Slowly increase the
LC
)
December 29, 2004
C
from
(EQ. 27)
PP
FN9085.7
is