ISL6526CBZ Intersil, ISL6526CBZ Datasheet - Page 11

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ISL6526CBZ

Manufacturer Part Number
ISL6526CBZ
Description
IC CTRLR PWM SYNC BUCK 14-SOIC
Manufacturer
Intersil
Datasheet

Specifications of ISL6526CBZ

Pwm Type
Voltage Mode
Number Of Outputs
1
Frequency - Max
325kHz
Duty Cycle
100%
Voltage - Supply
2.97 V ~ 3.63 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
14-SOIC (3.9mm Width), 14-SOL
Frequency-max
325kHz
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
ISL6526CBZ-T
Manufacturer:
INTERSIL
Quantity:
8 270
Part Number:
ISL6526CBZ-T
Manufacturer:
INTERSIL
Quantity:
14 263
Component Selection Guidelines
Charge Pump Capacitor Selection
A capacitor across pins CT1 and CT2 is required to create
the proper bias voltage for the ISL6526, ISL6526A when
operating the IC from 3.3V. Selecting the proper capacitance
value is important so that the bias current draw and the
current required by the MOSFET gates do not overburden
the capacitor. A conservative approach is presented in
Equation 10.
Output Capacitor Selection
An output capacitor is required to filter the output and supply
the load transient current. The filtering requirements are a
function of the switching frequency and the ripple current.
The load transient requirements are a function of the slew
rate (di/dt) and the magnitude of the transient load current.
These requirements are generally met with a mix of
capacitors and careful layout.
Modern digital ICs can produce high transient load slew
rates. High frequency capacitors initially supply the transient
and slow the current load rate seen by the bulk capacitors.
The bulk filter capacitor values are generally determined by
the ESR (Effective Series Resistance) and voltage rating
requirements rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the power pins of the load as physically possible. Be
careful not to add inductance in the circuit board wiring that
could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements.
Use only specialized low-ESR capacitors intended for
switching-regulator applications for the bulk capacitors. The
bulk capacitor’s ESR will determine the output ripple voltage
and the initial voltage drop after a high slew-rate transient. An
aluminum electrolytic capacitor’s ESR value is related to the
case size with lower ESR available in larger case sizes.
However, the Equivalent Series Inductance (ESL) of these
capacitors increases with case size and can reduce the
usefulness of the capacitor to high slew-rate transient loading.
Unfortunately, ESL is not a specified parameter. Work with
your capacitor supplier and measure the capacitor’s
impedance with frequency to select a suitable component. In
most cases, multiple electrolytic capacitors of small case size
perform better than a single large case capacitor.
Output Inductor Selection
The output inductor is selected to meet the output voltage
ripple requirements and minimize the converter’s response
time to the load transient. The inductor value determines the
converter’s ripple current and the ripple voltage is a function
C
PUMP
=
I
------------------------------------
BiasAndGate
V
CC
×
f
s
×
1.5
11
ISL6526, ISL6526A
(EQ. 10)
of the ripple current. The ripple voltage and current are
approximated by Equations 11 and 12:
Increasing the value of inductance reduces the ripple current
and voltage. However, the large inductance values reduce
the converter’s response time to a load transient.
One of the parameters limiting the converter’s response to
a load transient is the time required to change the inductor
current. Given a sufficiently fast control loop design, the
ISL6526, ISL6526A will provide either 0% or 100% duty
cycle in response to a load transient. The response time is
the time required to slew the inductor current from an initial
current value to the transient current level. During this
interval, the difference between the inductor current and
the transient current level must be supplied by the output
capacitor. Minimizing the response time can minimize the
output capacitance required.
The response time to a transient is different for the
application of load and the removal of load. Equations 13
and 14 give the approximate response time interval for
application and removal of a transient load:
t
t
where: I
response time to the application of load, and t
response time to the removal of load. The worst case
response time can be either at the application or removal of
load. Be sure to check both of these equations at the
minimum and maximum output levels for the worst case
response time.
Input Capacitor Selection
Use a mix of input bypass capacitors to control the voltage
overshoot across the MOSFETs. Use small ceramic
capacitors for high frequency decoupling and bulk capacitors
to supply the current needed each time Q
small ceramic capacitors physically close to the MOSFETs
and between the drain of Q
The important parameters for the bulk input capacitor are the
voltage rating and the RMS current rating. For reliable
operation, select the bulk capacitor with voltage and current
ratings above the maximum input voltage and largest RMS
current required by the circuit. The capacitor voltage rating
should be at least 1.25 times greater than the maximum
ΔV
RISE
FALL
ΔI =
OUT
=
=
V
TRAN
= ΔI x ESR
IN
L x I
V
f
L x I
s
- V
IN
V
x L
OUT
TRAN
- V
OUT
TRAN
is the transient load current step, t
OUT
x
V
V
OUT
IN
1
and the source of Q
1
turns on. Place the
FALL
November 24, 2008
2
RISE
.
is the
(EQ. 12)
(EQ. 13)
(EQ. 14)
(EQ. 11)
FN9055.10
is the

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