ISL6569CRZ-T Intersil, ISL6569CRZ-T Datasheet - Page 19

• 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

The first step is to choose the desired bandwidth, f
compensated system. Choose a frequency high enough to
assure adequate transient performance but not higher than
1/3 of the switching frequency. The type-III compensator has
an extra high-frequency pole, f
added noise rejection or to assure adequate attenuation at
the error-amplifier high-order pole and zero frequencies. A
good general rule is to chose f
if desired. Choosing f
problems with too much phase shift below the system
bandwidth.
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
Equations 28, R
compensation components are then selected according to
Equations 28.
In Equations 28, L is the per-channel filter inductance
divided by the number of active channels; C is the sum total
of all output capacitors; ESR is the equivalent-series
R
C
C
R
C
FIGURE 14. COMPENSATION CIRCUIT FOR ISL6569 BASED
1
1
2
C
C
=
=
=
=
=
C
R
R
---------------------------------------- -
------------------------------------------------------------------ -
(
-------------------------------------------------------------------- -
0.75 V
------------------------------------------------------------------ -
(
2π
1
0.75V
1
2π
V
LC C ESR
FB
PP
)
)
2
---------------------------------------- -
2
–
R
f


f
LC C ESR
0
IN
0
2π
FB
IN
f
C ESR
f
CONVERTER WITHOUT LOAD-LINE
REGULATION.
0.75V
HF
(
HF




(
–


2πf
2πf
2
FB
f
0
LCR
(
LCR
HF
R
f
HF
IN
is selected arbitrarily. The remaining
)
HF
FB
R
)
HF
C
LCR
FB
LC 1
FB
LC 1
)
C
to be lower than 10 f
V
2
V
–
–
C
PP
FB
PP
C




19
HF
HF
. This pole can be used for
= 10 f
COMP
VDIFF
IOUT
FB
0
, but it can be higher
0
can cause
0
, of the
(EQ. 28)
ISL6569
resistance of the bulk output-filter capacitance; and V
the peak-to-peak sawtooth signal amplitude as described in
Figure 5 and Electrical Specifications.
Input Supply Voltage Selection
The VCC input of the ISL6569 can be connected to either a
+5V supply directly or through a current limiting resistor to a
+12V supply. An integrated 5.8V shunt regulator maintains
the voltage on the VCC pin when a +12V supply is used. A
300Ω resistor is suggested for limiting the current into the
VCC pin to approximately 20mA.
Switching Frequency
There are a number of variables to consider when choosing
the switching frequency, as there are considerable effects on
the upper-MOSFET loss calculation. These effects are
outlined in MOSFETs, and they establish the upper limit for
the switching frequency. The lower limit is established by the
requirement for fast transient response and small output-
voltage ripple as outlined in Input Supply Voltage Selection.
Choose the lowest switching frequency that allows the
regulator to meet the transient-response requirements.
Switching frequency is determined by the selection of the
frequency-setting resistor, RT (see the figure Typical
Application on page 4). Figure 15 and Equation 29 are
provided to assist in the selecting the correct value for R
Input Capacitor Selection
The input capacitors are responsible for sourcing the ac
component of the input current flowing into the upper
MOSFETs. Their RMS current capacity must be sufficient to
handle the ac component of the current drawn by the upper
MOSFETs which is related to duty cycle and the number of
active phases.
R
T
1000
100
=
10
10
10
[
FIGURE 15. R
11.09 1.13
–
SWITCHING FREQUENCY (KHZ)
log
( )
f
T
S
100
VS SWITCHING FREQUENCY
]
1000
December 29, 2004
(EQ. 29)
PP
FN9085.7
10000
T
is
.