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Data Sheet
April 27, 2009
ISL6420B
FN6901.0
Advanced Single Synchronous Buck
Pulse-Width Modulation (PWM) Controller
The ISL6420B simplifies the implementation of a complete
control and protection scheme for a high-performance
DC/DC buck converter. It is designed to drive N-channel
MOSFETs in a synchronous rectified buck topology, the
ISL6420B integrates control, output adjustment, monitoring
and protection functions into a single package. Additionally,
the IC features an external reference voltage tracking mode
for externally referenced buck converter applications and
DDR termination supplies, as well as a voltage margining
mode for system testing in networking DC/DC converter
applications.
The ISL6420B provides simple, single feedback loop,
voltage mode control with fast transient response. The
output voltage of the converter can be precisely regulated to
as low as 0.6V.
The operating frequency is fully adjustable from 100kHz to
1.4MHz. High frequency operation offers cost and space
savings.
The error amplifier features a 15MHz gain-bandwidth
product and 6V/µs slew rate that enables high converter
bandwidth for fast transient response. The PWM duty cycle
ranges from 0% to 100% in transient conditions. Selecting
the capacitor value from the ENSS pin to ground sets a fully
adjustable PWM soft-start. Pulling the ENSS pin LOW
disables the controller.
The ISL6420B monitors the output voltage and generates a
PGOOD (power good) signal when soft-start sequence is
complete and the output is within regulation. A built-in
overvoltage protection circuit prevents the output voltage
from going above typically 115% of the set point. Protection
from overcurrent conditions is provided by monitoring the
rDS(ON) of the upper MOSFET to inhibit the PWM operation
appropriately. This approach simplifies the implementation
and improves efficiency by eliminating the need for a current
sensing resistor.
Features
• Operates From:
- 4.5V to 5.5V Input
- 5.5V to 28V Input
• 0.6V Internal Reference Voltage
- ±2.0% Reference Accuracy
• Resistor-Selectable Switching Frequency
- 100kHz to 1.4MHz
• Voltage Margining and External Reference Tracking
Modes
• Output Can Sink or Source Current
• Lossless, Programmable Overcurrent Protection
- Uses Upper MOSFET’s rDS(ON)
• Programmable Soft-Start
• 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
• Extensive Circuit Protection Functions
- PGOOD, Overvoltage, Overcurrent, Shutdown
• Diode Emulation during Startup for Pre-Biased Load
Applications
• Offered in 20 Ld QFN and QSOP Packages
• QFN (4x4) Package
- QFN compliant to JEDEC PUB95 MO-220 QFN - Quad
Flat No Leads - Product Outline
- QFN Near Chip Scale Package Footprint; Improves
PCB Efficiency, Thinner in Profile
• Pb-Free (RoHS Compliant)
Applications
• Power Supplies for Microprocessors/ASICs
- Embedded Controllers
- DSP and Core Processors
- DDR SDRAM Bus Termination
• Ethernet Routers and Switchers
• High-Power DC/DC Regulators
• Distributed DC/DC Power Architecture
• Personal Computer Peripherals
• Externally Referenced Buck Converters
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. 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.

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ISL6420B
www.ODartadSehereint4Ug.cIonmformation
PART NUMBER
(Note)
PART
MARKING
TEMP.
RANGE (°C)
PACKAGE
(Pb-Free)
PKG.
DWG. #
ISL6420BIAZ
6420 BIAZ
-40 to +85
20 Ld QSOP
M20.15
ISL6420BIAZ-TK*
6420 BIAZ
-40 to +85
20 Ld QSOP
M20.15
ISL6420BIRZ
6420 BIRZ
-40 to +85
20 Ld 4x4 QFN
L20.4x4
ISL6420BIRZ-TK*
6420 BIRZ
-40 to +85
20 Ld 4x4 QFN
L20.4x4
*Please refer to TB347 for details on reel specifications.
NOTE: These Intersil Pb-free plastic packaged products employ special Pb-free material sets, molding compounds/die attach materials, and 100%
matte tin plate plus anneal (e3 termination finish, which is 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.
Pinouts
ISL6420B
(20 LD QFN)
TOP VIEW
20 19 18 17 16
GPIO2 1
GPIO1/REFIN 2
OCSET 3
REFOUT 4
VMSET/MODE 5
15 PGND
14 CDEL
13 PGOOD
12 ENSS
11 COMP
6 7 8 9 10
ISL6420B
(20 LD QSOP)
TOP VIEW
CDEL 1
PGND 2
LGATE 3
PVCC 4
PHASE 5
UGATE 6
BOOT 7
GPIO2 8
GPIO1/REFIN 9
OCSET 10
20 PGOOD
19 ENSS
18 COMP
17 FB
16 RT
15 SGND
14 VIN
13 VCC5
12 VMSET/MODE
11 REFOUT
2 FN6901.0
April 27, 2009

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www.FDautanScheteiot4Un.acolmBlock Diagram
ISL6420B
SGND
FB
COMP
GPIO1/REFIN
GPIO2
REFOUT
VMSET/MODE
VCC5 VIN
OCSET
LDO
REFERENCE
SS 0.6V
PHASE
OVERCURRENT
+ COMP
- OCFLT
OVFLT
UVFLT
FAULT
LOGIC
ERROR
AMP
+
-
+
-
PWM
COMP
PWM
LOGIC
VOLTAGE
MARGINING
FB
RAMP
GENERATOR
OV/UV
VOLTAGE
MONITOR
OVFLT
UVFLT
OSC
RT
PHASE
LOGIC
EN/SS
ENSS
Typical 5V Input DC/DC Application Schematic
5V
C1
C7
0.1µF
R2
C8
C2 C3
VIN PVCC
VCC5
ENSS
RT
MONITOR AND
PROTECTION
PGOOD
CDEL
SGND
FB
OSC
REF
+
-
--
+
+
C4 C5
OCSET R1
BOOT
UGATE
PHASE
Q1
LGATE
PGND
R3
R4
COMP
C11
R5 C12
R6
VMSET/MODE
GPIO1/REFIN
GPIO2
REFOUT
C13
Q2
D1
C9
C6
L1
C10
BOOT
UGATE
PHASE
PVCC
LGATE
PGND
PGOOD
CDEL
3.3V
3 FN6901.0
April 27, 2009

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ISL6420B
www.TDaytapSihceaetl4U1.2coVm Input DC/DC Application Schematic
12V
C7
C1
R2
C8
C2 C3
VIN PVCC
VCC5
ENSS
RT
PGOOD
CDEL
SGND
FB
MONITOR AND
PROTECTION
OSC
REF
+
-
-
+
C4
OCSET
BOOT
UGATE
PHASE
LGATE
PGND
C5
R1
Q1
R3
R4
COMP
C11
R5 C12
GPIO1/REFIN
GPIO2
R6 REFOUT
C13
VMSET/MODE
Q2
D1
C9
C6
L1
C10
3.3V
Typical 5V Input DC/DC Application Schematic
5V
C1
C2
C3 C4 C5
VIN PVCC
VCC5
D1
SS/EN
RT
MONITOR AND
PROTECTION
OCSET R1
BOOT
Q1
CDEL
OSC
C7 R2
PGOOD
UGATE
PHASE
REF
C8
SGND
-
FB
+
-
+
LGATE
PGND
Q2
C6
L1
C9
R3
R4
COMP
C10
C11 R5
VMSET/MODE
VCC5
GPIO1/REFIN <-- VREF = VDDQ/2
GPIO2
REFOUT
1.25V VREF
C12 TO REFIN OF VTT SUPPLY
CONFIGURATION FOR DDR TERMINATION/EXTERNALLY REFERENCED TRACKING APPLICATIONS
2.5V/1.25V
4 FN6901.0
April 27, 2009

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ISL6420B
www.TDaytapSihceaetl4U1.2coVm Input DC/DC Application Schematic
12V
C7
C1
R2
R3
C6
C2 C3 C4
VIN PVCC
VCC5
SS/EN
RT
MONITOR AND
PROTECTION
OCSET
BOOT
CDEL
PGOOD
SGND
FB
OSC
REF
+
-
-
+
UGATE
PHASE
LGATE
PGND
C5
R1
Q1
Q2
D1
C8
L1
C9
COMP
C10
C11 R5
R4 VMSET/MODE
VCC5
GPIO1/REFIN <-- VREF = VDDQ/2
GPIO2
REFOUT
C12
1.25V VREF
TO REFIN OF VTT SUPPLY
CONFIGURATION FOR DDR TERMINATION/EXTERNALLY REFERENCED TRACKING APPLICATIONS
2.5V/1.25V
VDDQ/VTT
5 FN6901.0
April 27, 2009