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Data Sheet
August 23, 2011
ISL6721A
FN6797.0
Flexible Single-ended Current Mode PWM
Controller
The ISL6721A is a low power, single-ended pulse width
modulating (PWM) current mode controller designed for a
wide range of DC/DC conversion applications including
boost, flyback, and isolated output configurations. Peak
current mode control effectively handles power transients
and provides inherent overcurrent protection. Other features
include a low power mode where the supply current drops to
less than 200µA during overvoltage and overcurrent
shutdown faults. It differs from the ISL6721 in that the UVLO
and UV thresholds have been modified.
This advanced BiCMOS design features low operating
current, adjustable operating frequency up to 1MHz,
adjustable soft-start, and a bidirectional SYNC signal that
allows the oscillator to be locked to an external clock for
noise sensitive applications.
Applications
• Telecom and Datacom Power
• Wireless Base Station Power
• File Server Power
• Industrial Power Systems
• Isolated Buck and Flyback Regulators
• Boost Regulators
Pinouts
ISL6721A
(16 LD TSSOP)
TOP VIEW
GATE 1
ISENSE 2
SYNC 3
SLOPE 4
UV 5
OV 6
RTCT 7
ISET 8
16 VC
15 PGND
14 VCC
13 VREF
12 LGND
11 SS
10 COMP
9 FB
Features
• 1A MOSFET Gate Driver
• 100µA Startup Current
• Fast Transient Response with Peak Current Mode Control
• Adjustable Switching Frequency up to 1MHz
• Bidirectional Synchronization
• Low Power Disable Mode
• Delayed Restart from OV and OC Shutdown Faults
• Adjustable Slope Compensation
• Adjustable Soft-start
• Adjustable Overcurrent Shutdown Delay
• Adjustable UV and OV Monitors
• Leading Edge Blanking
• Integrated Thermal Shutdown
• 1% Tolerance Voltage Reference
• Pb-Free (RoHS Compliant)
ISL6721A
(16 LD QFN)
TOP VIEW
16 15 14 13
SYNC 1
SLOPE 2
UV 3
OV 4
12 VCC
11 VREF
10 LGND
9 SS
5678
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas Inc. 2003-2005, 2007, 2008, 2011. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.

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ISL6721A
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
PART MARKING
TEMP RANGE (°C)
PACKAGE
PKG. DWG. #
ISL6721AARZ
21AZ
-40 to +105 16 Ld QFN
L16.3x3B
ISL6721AAVZ
6721A AVZ
-40 to +105 16 Ld TSSOP
M16.173
NOTES:
1. *Add “-T*” suffix for tape and reel. Please refer to TB347 for details on reel specifications.
2. 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.
3. For Moisture Sensitivity Level (MSL), please see device information page for ISL6721A. For more information on MSL please see
Tech Brief TB363.
2 FN6797.0
August 23, 2011

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Functional Block Diagram
ISL6721A
VCC
LGND
ISET
ISENSE
5k
START/STOP
UV COMPARATOR
+
-
VREF
5.00 V
1%
ENABLE
BG +-
THERMAL
PROTECTION
RESTART
DELAY
0.8
VREF
53µA
+
Σ
+
100mV
- OC DETECT
+
OVERCURRENT
COMPARATOR
SS CHARGE
VOLTAGE CLAMP
SS CHARGED
SHTDN
SOFT-START
CHARGE 70µA
CURRENT
ON
OC
FAULT
OC
25µA
+
-
4.375V
SS DCHG ON
OVERCURRENT
SHUTDOWN
DELAY
SS CHG
SLOPE
0.1
COMP
SS
SS CLAMP
+
-
VFB
2.5V
ERROR
AMPLIFIE
R
+
-
PWM
COMPARATOR
+
-
1/3 100nS START
BLANKING
SS LOW
-
+
FAULT
LATCH
SS LOW 270mV
COMPARATOR
SQ
RQ
SET DOMINANT
VREF
UV COMPARATOR
4.65V -
+
BG
VREF
VREF
SS
15µA
VREF
20K 3.0V
1.5V 12k
30K
RTCT
VREF
OSCILLATOR
COMPARATOR
-
+
1mA
ON
+
4V -
-
2V +
ON
Bi-Directional
Synchronization
OSC IN
CLK OUT
NO EXT SYNC
EXT SYNC BLANKING
SYNC IN
SYNC OUT
VREF
SQ
RQ
BLANKING
COMPARATOR
3.0V
-
+
+
-
2.50V
-
+
1.93V
36k
OV
UV
VC
GATE
PGND
SYNC
100
4.5k
3 FN6797.0
August 23, 2011

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ISL6721A
Typical Application - 48V Input Dual
Output Flyback, 3.3V @ 2.5A, 1.8V @ 1.0A
SP1 SP2
VIN+ P9
36-75V
C1
VIN-
R1
R2
SYNC
R5
R6
Q3
VR1
R24
C2
C18
CR6
C3 TP1
Q1
T1
ISOLATION
XFMR
CR5
R21
C21 + C15
C5 CR2
CR4
C19 +
C17
C22
+
C20
R16 R17
C6
R19
U2
C14
+ C16
+3.3V
+1.8V
RETURN
R18
R4 R3
R23
R25
C4
Q2
D1
TP3
TP5
D2
R22
TP2
U4
GATE
ISENSE
SYNC
SLOPE
UV
OV
RTCT
ISET
VC
PGND
VCC
VREF
LGND
SS
COMP
VFB
R8
R10
C7 C8
R7 R12
R11
R9
R15
C13
U3
R20
R26
R27
C9
R13
R14
TP4
C12
C11
C10
4 FN6797.0
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Typical Boost Converter Application
Schematic
ISL6721A
VIN+
L1
C1
VIN-
CR1
R12 C12
Q1
R1 R2
R3
R4
+
C2
C3
C11
+VOUT
RETURN
R8
R5
C9
VIN+
C4 U1
GATE
VC
ISENSE PGND
SYNC VCC
SLOPE VREF
UV LGND
OV SS
RTCT COMP
ISET VFB
R10 C10
R9
R11
C8
R7
R6
C5
C7 C6
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