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PDF ISL6526A Data sheet ( Hoja de datos )
| Número de pieza | ISL6526A | |
| Descripción | Single Synchronous Buck Pulse-Width Modulation (PWM) Controller | |
| Fabricantes | Intersil Corporation | |
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Data Sheet
ISL6526, ISL6526A
March 20, 2007
FN9055.8
Single Synchronous Buck Pulse-Width
Modulation (PWM) Controller
The ISL6526, ISL6526A make simple work out of
implementing a complete control and protection scheme for
a DC/DC stepdown converter. Designed to drive N-Channel
MOSFETs in a synchronous buck topology, the ISL6526,
ISL6526A integrate the control, output adjustment,
monitoring and protection functions into a single package.
The ISL6526, ISL6526A provide simple, single feedback
loop, voltage-mode control with fast transient response. The
output voltage can be precisely regulated to as low as 0.8V,
with a maximum tolerance of ±1.5% over temperature and
line voltage variations. A fixed frequency oscillator reduces
design complexity, while balancing typical application cost
and efficiency.
The error amplifier features a 15MHz gain-bandwidth
product and 6V/μs slew rate which enables high converter
bandwidth for fast transient performance. The resulting
PWM duty cycles range from 0% to 100%.
Protection from overcurrent conditions is provided by
monitoring the rDS(ON) of the upper MOSFET to inhibit PWM
operation appropriately. This approach simplifies the
implementation and improves efficiency by eliminating the
need for a current sense resistor.
Features
• Operates from 3.3V to 5V Input
• 0.8V to VIN Output Range
- 0.8V Internal Reference
- ±1.5% Over Load, Line Voltage and Temperature
• Drives N-Channel MOSFETs
• Simple Single-Loop Control Design
- Voltage-Mode PWM Control
• Fast Transient Response
- High-Bandwidth Error Amplifier
- Full 0% to 100% Duty Cycle
• Lossless, Programmable Overcurrent Protection
- Uses Upper MOSFET’s rDS(on)
• Converter can Source and Sink Current
• Small Converter Size
- Internal Fixed Frequency Oscillator
- ISL6526: 300kHz
- ISL6526A: 600kHz
• Internal Soft-Start
• 14 Lead SOIC or 16 Lead 5x5 QFN
• QFN Package:
- Compliant to JEDEC PUB95 MO-220 QFN - Quad Flat
No Leads - Package Outline
- Near Chip Scale Package footprint, which improves
PCB efficiency and has a thinner profile
• Pb-Free Plus Anneal Available (RoHS Compliant)
Applications
• Power Supplies for Microprocessors
- PCs
- Embedded Controllers
• Subsystem Power Supplies
- PCI/AGP/GTL+ Buses
- ACPI Power Control
- DDR SDRAM Bus Termination Supply
• Cable Modems, Set Top Boxes, and DSL Modems
• DSP and Core Communications Processor Supplies
• Memory Supplies
• Personal Computer Peripherals
• Industrial Power Supplies
• 3.3V-Input DC/DC Regulators
• Low-Voltage Distributed Power Supplies
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2001-2005, 2007. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL6526, ISL6526A
Absolute Maximum Ratings
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7.0V
Absolute Boot Voltage, VBOOT . . . . . . . . . . . . . . . . . . . . . . . +15.0V
Upper Driver Supply Voltage, VBOOT - VPHASE . . . . . . . . . . . +7.0V
Input, Output or I/O Voltage . . . . . . . . . . . GND -0.3V to VCC +0.3V
ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 2
Operating Conditions
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . +3.3V ±10%
Ambient Temperature Range . . . . . . . . . . . . . . . . . . .-40°C to +85°C
Junction Temperature Range. . . . . . . . . . . . . . . . . .-40°C to +125°C
Thermal Information
Thermal Resistance
θJA (°C/W)
θJC (°C/W)
SOIC Package (Note 1) . . . . . . . . . . . .
67
N/A
QFN Package (Note 2). . . . . . . . . . . . .
35
5
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . +150°C
Maximum Storage Temperature Range . . . . . . . . . .-65°C to +150°C
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . +300°C
(SOIC - Lead Tips Only)
For Recommended soldering conditions see Tech Brief TB389.
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES:
1. θJA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
2. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. θJC, the
“case temp” is measured at the center of the exposed metal pad on the package underside. See Tech Brief TB379.
Electrical Specifications Recommended Operating Conditions, unless otherwise noted VCC = 3.3V ±5% and TA = +25°C
PARAMETER
SYMBOL
TEST CONDITIONS
MIN TYP MAX
VCC SUPPLY CURRENT
Nominal Supply
POWER-ON RESET
IBIAS
6.1 6.9 7.7
Rising CPVOUT POR Threshold
POR Commercial
4.25 4.30 4.42
Industrial
4.10 4.30 4.50
CPVOUT POR Threshold Hysteresis
0.3 0.6 0.9
OSCILLATOR
Frequency
fOSC
IC = ISL6526C, Commercial
IC = ISL6526I, Industrial
275 300 325
250 300 340
IC = ISL6526AC, Commercial
530 600 645
IC = ISL6526AI, Industrial
510 600 650
Ramp Amplitude
REFERENCE
ΔVOSC
- 1.5 -
Reference Voltage Tolerance
- - 1.5
Nominal Reference Voltage
CHARGE PUMP
VREF
- 0.800 -
Nominal Charge Pump Output
Charge Pump Output Regulation
VCPVOUT VVCC = 3.3V, No Load
- 5.1 -
-2-
ERROR AMPLIFIER
DC Gain
Guaranteed by Design
- 88 -
Gain-Bandwidth Product
GBWP
- 15 -
Slew Rate
SR
-6-
SOFT-START
Soft-Start Slew Rate
Commercial
6.2 - 7.3
Industrial
6.2 - 7.6
UNITS
mA
V
V
V
kHz
kHz
kHz
kHz
VP-P
%
V
V
%
dB
MHz
V/μs
ms
ms
5 FN9055.8
March 20, 2007
5 Page 
ISL6526, ISL6526A
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 the
following equation.
CPUMP
=
I--B----i--a---s---A----n---d----G----a----t-e--
VCC × fs
×
1.5
(EQ. 5)
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
of the ripple current. The ripple voltage and current are
approximated by the following equations:
ΔI = VIN - VOUT x VOUT
fs x L
VIN
ΔVOUT = ΔI x ESR
(EQ. 6)
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. The following
equations give the approximate response time interval for
application and removal of a transient load:
tRISE =
L x ITRAN
VIN - VOUT
tFALL =
L x ITRAN
VOUT
(EQ. 7)
where: ITRAN is the transient load current step, tRISE is the
response time to the application of load, and tFALL is the
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 Q1 turns on. Place the
small ceramic capacitors physically close to the MOSFETs
and between the drain of Q1 and the source of Q2.
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
input voltage and a voltage rating of 1.5 times is a
conservative guideline. The RMS current rating requirement
for the input capacitor of a buck regulator is approximately
1/2 the DC load current.
11 FN9055.8
March 20, 2007
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet ISL6526A.PDF ] | |
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