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®
Data Sheet
January 17, 2006
ISL6535
FN9255.0
Synchronous Buck Pulse-Width
Modulator (PWM) Controller
The ISL6535 is a high performance synchronous controller
for demanding DC/DC converter applications. It provides
overcurrent fault protection and is designed to safely startup
into prebiased output loads.
The output voltage of the converter can be precisely
regulated to as low as 0.597V, with a maximum tolerance of
±1% over the commercial temperature range, and ±1.5%
over the industrial temperature range.
The ISL6535 provides simple, single feedback loop, voltage-
mode control with fast transient response. It includes a
triangle-wave oscillator that is adjustable from below 50kHz
to over 1.5MHz. Full (0% to 100%) PWM duty cycle support
is provided.
The error amplifier features a 15MHz gain-bandwidth
product and 6V/µs slew rate which enables high converter
bandwidth for fast transient performance.
The ISL6535's overcurrent protection monitors the current
by using the rDS(ON) of the upper MOSFET which eliminates
the need for a current sensing resistor.
Pinouts
ISL6535
(14 LD NARROW SOIC AND 16 LD QFN)
TOP VIEW
RT 1
OCSET 2
SS 3
COMP 4
FB 5
EN 6
GND 7
14 VCC
13 PVCC
12 LGATE
11 PGND
10 BOOT
9 UGATE
8 PHASE
16 15 14 13
SS 1
COMP 2
FB 3
EN 4
12 PVCC
11 LGATE
10 PGND
9 BOOT
5678
Features
• Operates from +12V Input
• Excellent Output Voltage Regulation
- 0.597V Internal Reference
- ±1% Over the Commercial Temperature Range
- ±1.5% Over the Industrial Temperature Range
• Simple Single-Loop Control Design
- Voltage-Mode PWM Control
• Fast Transient Response
- High-Bandwidth Error Amplifier
- Full 0% to 100% Duty Ratio
- Leading and Falling Edge Modulation
• Small Converter Size
- Constant Frequency Operation
- Oscillator Programmable from 50kHz to Over 1.5MHz
• 12V High Speed MOSFET Gate Drivers
- 2.0A Source/3A Sink at 12V Low Side Gate Drive
- 1.25A Source/2A Sink at 12V High Side Gate Drive
- Drives Two N-Channel MOSFETs
• Overcurrent Fault Monitor
- High-Side MOSFET’s rDS(ON) Sensing
- Reduced ~120ns Blanking Time
• Converter can Source and Sink Current
• Soft-Start Done and an External Reference Pin for
Tracking Applications are Available in the QFN Package
• Pin Compatible with ISL6522
• Supports Start-Up into Prebiased Loads
• Pb-Free Plus Anneal Available (RoHS Compliant)
Applications
• Power Supply for some Pentium®, PowerPC™, as well as
Graphic CPUs
• High-Power 12V Input DC/DC Regulators
• Low-Voltage Distributed Power Supplies
Ordering Information
PART
NUMBER
(Note)
PART
MARKING
TEMP.
RANGE
(°C)
PACKAGE
(Pb-free)
PKG.
DWG. #
ISL6535CBZ 6535CBZ 0 to 70 14 Ld SOIC M14.15
ISL6535IBZ 6535IBZ -40 to 85 14 Ld SOIC M14.15
ISL6535CRZ 6535CRZ 0 to 70 16 Ld 4x4 QFN L16.4x4
ISL6535IRZ 6535IRZ -40 to 85 16 Ld 4x4 QFN L16.4x4
Add “-T” suffix for tape and reel.
NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets;
molding compounds/die attach materials and 100% matte tin plate termination finish,
which are RoHS compliant and compatible with both SnPb and Pb-free soldering
operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow
temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
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. 2006. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.

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Block Diagram
EN SS
REFIN
(QFN ONLY)
6µA REFERENCE
VREF = 0.597 V
30µA
POWER-ON
RESET (POR)
SOFT-START
AND
FAULT LOGIC
VCC
INTERNAL
REGULATOR
SOURCE OCP
200µA
OCSET
BOOT
UGATE
FB
COMP
GND
GATE
CONTROL
LOGIC
EA
PWM
OSCILLATOR
SSDONE
(QFN ONLY)
RT
PHASE
PVCC
LGATE
PGND

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Simplified Power System Diagram
ISL6535
+12V
Cvcc
RFS
ISL6535
ROCSET
+1.2V to +12VIN
Q1
LOUT
COUT
Q2
CSS
R2
R1
VOUT
Typical Application
+12VIN
RFILTER
CF1
VCC
SSDONE
(QFN ONLY)
REFIN
(QFN ONLY)
LIN
CF2 DBOOT
CHFIN
PVCC
BOOT
OCSET
UGATE
ROCSET
COCSET
Q1
PHASE
EN
LGATE
Q2
RRT
RT
ISL6535
PGND
CBIN
CBOOT
LOUT
CHFOUT
SS
CSS
COMP
C1
FB
GND
C2
R2
RO
C3 R3
R1
VOUT
CBOUT
3 FN9255.0
January 17, 2006

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ISL6535
Absolute Maximum Ratings
Supply Voltage, VPVCC,VVCC . . . . . . . . . . . . . . GND - 0.3V to +16V
Enable Voltage, VEN . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to +16V
Soft-start Done Voltage, VSSDONE . . . . . . . . . . GND - 0.3V to +16V
Boot Voltage, VBOOT . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to +36V
Phase Voltage, VPHASE . . . . . . . . . VBOOT - 16V to VBOOT + 0.3V
All Other Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to 5.0V
Operating Conditions
Supply Voltage, VVCC . . . . . . . . . . . . . . . . . . . . . . . . . . +12V ±10%
Supply Voltage, VPVCC . . . . . . . . . . . . . . . . . . . . . . . . . +12V ±10%
Boot to Phase Voltage, VBOOT - VPHASE . . . . . . . . . . . . . . <VPVCC
Ambient Temperature Range, ISL6535C . . . . . . . . . . . . 0°C to 70°C
Ambient Temperature Range, ISL6535I. . . . . . . . . . . .-40°C to 85°C
Thermal Information
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
SOIC Package (Note 1) . . . . . . . . . . . .
95
N/A
QFN Package (Note 2). . . . . . . . . . . . .
47
8.5
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)
ESD Ratings
ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 2
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 an evaluation PC board in free air.
2. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See
Tech Brief TB379. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
3. Parameters designated by GBD are "Guaranteed by Design."
Electrical Specifications
PARAMETER
VCC SUPPLY CURRENT
Shutdown Supply VCC
Shutdown Supply VPVCC
POWER-ON RESET
VCC/VPVCC Rising Threshold
VCC/VPVCC Hysteresis
OCSET Rising Threshold
OCSET Hysteresis
Enable - Rising Threshold
Enable - Hysteresis
OSCILLATOR
Trim Test Frequency
Total Variation
Ramp Amplitude
ERROR AMPLIFIER
DC Gain
Gain-Bandwidth Product
Slew Rate
PROTECTION
OCSET Current
OCSET Current
OCSET Measurement Offset
Soft-start Current
Recommended Operating Conditions, unless otherwise noted specifications in bold are valid for process,
temperature, and line operating conditions.
SYMBOL
TEST CONDITIONS
MIN TYP MAX UNITS
IVCC
IPVCC
SS/EN = 0V
SS/EN = 0V
3.5 6.1 8.5
0.30 0.5 0.75
6.55 7.10 7.55
170 250 500
0.70 0.73 0.75
180 200 220
1.4 1.5 1.60
175 250 325
mA
mA
V
mV
V
mV
V
mV
VOSC
RRT = OPEN VVCC = 12
8k< RRT to GND < 200k- GBD
RRT = OPEN
GBWP
SR
RL = 10k, CL= 100pF - GBD
RL = 10k, CL= 100pF - GBD
RL = 10k, CL= 100pF - GBD
IOCSET TJ = 0°C to 70°C
IOCSET TJ = -40°C to 85°C
OCPOFFSET OCSET= 1.5V to 15.4V - GBD
ISS
175 200 220
kHz
- ±15 -
%
1.7 1.9 2.15 VP-P
- 88 -
dB
- 15 - MHz
- 6 - V/µs
180 200 220
176 200 224
- ±10 -
22 30 38
µA
µA
mV
µA
4 FN9255.0
January 17, 2006

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ISL6535
Electrical Specifications Recommended Operating Conditions, unless otherwise noted specifications in bold are valid for process,
temperature, and line operating conditions. (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN TYP MAX UNITS
REFERENCE
Reference Voltage
System Accuracy
REFIN Current Source (QFN Only)
TJ = 0°C to 70°C
TJ = -40°C to 85°C
TJ = 0°C to 70°C
TJ = -40°C to 85°C
0.591
0.588
-1.0
-1.5
-4
0.597
0.597
-
-
-6
0.603
0.606
1.0
1.5
-8
V
V
%
%
µA
REFIN Threshold (QFN Only)
2.10 - 3.50
V
REFIN Offset (QFN Only)
-3 -
3 mV
GATE DRIVERS
Upper Drive Source Current
Upper Drive Source Impedance
Upper Drive Sink Current
Upper Drive Sink Impedance
Lower Drive Source Current
Lower Drive Source Impedance
Lower Drive Sink Current
Lower Drive Sink Impedance
SSDONE (QFN ONLY)
IU_SOURCE VBOOT - VPHASE = 12V, 3nF Load - GBD
RU_SOURCE 90mA Source Current
IU_SINK VBOOT - VPHASE = 12V, 3nF Load- GBD
RU_SINK 90mA Source Current
IL_SOURCE VPVCC = 12V, 3nF Load - GBD
RL_SOURCE 90mA Source Current
IL_SINK VPVCC = 12V, 3nF Load - GBD
RL_SINK 90mA Source Current
- 1.25 -
- 2.0 -
-2-
- 1.3 -
-2-
- 1.3 -
-3-
- 0.94 -
A
A
A
A
SSDONE Low Output Voltage
ISSDONE = 2mA
0.30 V
Typical Performance Curves
1000
RRT PULLUP
TO +12V
100
RRT PULLDOWN
TO GND
10
10 100
SWITCHING FREQUENCY (kHz)
FIGURE 1. RRT RESISTANCE vs FREQUENCY
1000
Functional Pin Description (SOIC/QFN)
RT (Pin 1/14)
This pin provides oscillator switching frequency adjustment.
By placing a resistor (RRT) from this pin to GND, the
switching frequency is set from between 200kHz and
1.5MHz according to the following equation: .
RRT[kΩ] ≈ -F---s----[--k---H-----z----]6---5–---0--2--0-0---0----[---k---H-----z----] 1.3k
(RRT to GND)
80
70
60
CGATE = 3300pF
50
CGATE = 1000pF
40
30
20
10 CGATE = 10pF
0
100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
FIGURE 2. BIAS SUPPLY CURRENT vs FREQUENCY
Alternately ISL6535’s switching frequency can be lowered
from 200kHz to 50kHz by connecting the RT pin with a
resistor to VCC according to the following equation:
RRT[kΩ] ≈ 2----0---0----[--k----H---5--z-5--]--0--–-0---F0----s---[---k---H-----z----] + 70k
(RRT to VCC)
5 FN9255.0
January 17, 2006