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PDF ISL6520B Data sheet ( Hoja de datos )
| Número de pieza | ISL6520B | |
| Descripción | Single Synchronous Buck Pulse-Width Modulation (PWM) Controller | |
| Fabricantes | Intersil Corporation | |
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®
Data Sheet
April 2003
ISL6520B
FN9083.1
Single Synchronous Buck Pulse-Width
Modulation (PWM) Controller
The ISL6520B makes simple work out of implementing a
complete control scheme for a DC-DC stepdown converter.
Designed to drive N-channel MOSFETs in a synchronous
buck topology, the ISL6520B integrates the control, output
adjustment and monitoring functions into a single 8-Lead
package.
The ISL6520B provides 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 8V/µs slew rate which enables high converter
bandwidth for fast transient performance. The resulting
PWM duty cycles range from 0% to 100%.
Ordering Information
TEMP.
PART NUMBER RANGE (oC)
PACKAGE
PKG.
NO.
ISL6520BCB
0 to 70 8 Ld SOIC
M8.15
ISL6520BIB
-40 to 85 8 Ld SOIC
M8.15
ISL6520BCR
0 to 70 16 Ld 4x4mm QFN L16.4x4
ISL6520BIR
-40 to 85 16 Ld 4x4mm QFN L16.4x4
ISL6520EVAL1 Evaluation Board
Pinouts
ISL6520B (8 LD SOIC)
TOP VIEW
BOOT 1
UGATE 2
GND 3
LGATE 4
8 PHASE
7 COMP/SD
6 FB
5 VCC
ISL6520B (16 LD QFN)
TOP VIEW
16 15 14 13
BOOT 1
12 NC
UGATE 2
GND 3
GND
11 COMP/SD
10 NC
NC 4
9 FB
5678
Features
• Operates from +5V Input
• 0.8V to VIN Output Range
- 0.8V Internal Reference
- ±1.5% Over 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
• Small Converter Size
- 300kHz Fixed Frequency Oscillator
- Internal Soft Start
- 8 Ld SOIC or 16Ld 4x4mm 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
Applications
• Power Supplies for Microprocessors
- PCs
- Embedded Controllers
• Subsystem Power Supplies
- PCI/AGP/GTL+ Buses
- ACPI Power Control
- SSTL-2 and 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
• 5V-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 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2003. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL6520B
rail, which supplies the bias voltage to the ISL6520B. If there
is nowhere for this current to go, such as to other distributed
loads on the VCC rail, through a voltage limiting protection
device, or other methods, the capacitance on the VCC bus
will absorb the current. This situation will allow voltage level
of the VCC rail to increase. If the voltage level of the rail is
boosted to a level that exceeds the maximum voltage rating
of the ISL6520B, then the IC will experience an irreversible
failure and the converter will no longer be operational.
Ensuring that there is a path for the current to follow other
than the capacitance on the rail will prevent this failure
mode.
Application Guidelines
Layout Considerations
As in any high frequency switching converter, layout is very
important. Switching current from one power device to another
can generate voltage transients across the impedances of the
interconnecting bond wires and circuit traces. These
interconnecting impedances should be minimized by using
wide, short printed circuit traces. The critical components
should be located as close together as possible, using ground
plane construction or single point grounding.
ISL6520B
VIN
UGATE
PHASE
LGATE
Q1
Q2
LO VOUT
CIN
CO
RETURN
FIGURE 2. PRINTED CIRCUIT BOARD POWER AND
GROUND PLANES OR ISLANDS
Figure 2 shows the critical power components of the converter.
To minimize the voltage overshoot, the interconnecting wires
indicated by heavy lines should be part of a ground or power
plane in a printed circuit board. The components shown in
Figure 2 should be located as close together as possible.
Please note that the capacitors CIN and CO may each
represent numerous physical capacitors. Locate the ISL6520B
within 3 inches of the MOSFETs, Q1 and Q2. The circuit traces
for the MOSFETs’ gate and source connections from the
ISL6520B must be sized to handle up to 1A peak current.
Figure 3 shows the circuit traces that require additional
layout consideration. Use single point and ground plane
construction for the circuits shown. Minimize any leakage
current paths on the COMP/SD pin and locate the resistor,
ROSCET close to the COMP/SD pin because the internal
current source is only 20µA. Provide local VCC decoupling
between VCC and GND pins. Locate the capacitor, CBOOT
as close as practical to the BOOT and PHASE pins. All
components used for feedback compensation should be
located as close to the IC a practical.
ISL6520B
BOOT
CBOOT
D1
PHASE
VCC +5V
+VIN
Q1 LO
Q2 CO
VOUT
GND
CVCC
FIGURE 3. PRINTED CIRCUIT BOARD SMALL SIGNAL
LAYOUT GUIDELINES
Feedback Compensation
Figure 4 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage
(VOUT) is regulated to the Reference voltage level. The
error amplifier (Error Amp) output (VE/A) is compared with
the oscillator (OSC) triangular wave to provide a
pulse-width modulated (PWM) wave with an amplitude of
VIN at the PHASE node. The PWM wave is smoothed by the
output filter (LO and CO).
∆ VOSC
OSC
PWM
COMPARATOR
-
+
DRIVER
DRIVER
VIN
LO
PHASE CO
VOUT
ZFB
VE/A
-
+
ZIN
ERROR REFERENCE
AMP
ESR
(PARASITIC)
DETAILED COMPENSATION COMPONENTS
C2
C1 R2
ZFB VOUT
ZIN
C3 R3
COMP/SD
- FB
+
ISL6520B
REFERENCE
R1
FIGURE 4. VOLTAGE-MODE BUCK CONVERTER
COMPENSATION DESIGN
The modulator transfer function is the small-signal transfer
function of VOUT/VE/A. This function is dominated by a DC
5
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