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Data Sheet
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ISL6521
FN9148.2
PWM Buck DC-DC and Triple Linear
Power Controller
The ISL6521 provides the power control and protection for
four output voltages in low-voltage, high-performance
applications. The IC integrates a voltage-mode PWM
controller and three linear controllers, as well as monitoring
and protection functions into a 16-lead SOIC package. The
PWM controller is intended to regulate the low voltage
supply that requires the greatest amount of current (usually
the core voltage for the FPGA, ASIC, or processor) with a
synchronous rectified buck converter. The linears are
intended to regulate other system voltages, such as I/O
(input/output) and memory circuits. Both the switching
regulator and linear voltage reference provide 2% of static
regulation over line, load, and temperature ranges. All
outputs are user-adjustable by means of an external resistor
divider. All linear controllers can supply up to 120mA with no
external pass devices. Employing bipolar NPNs for the pass
transistors, the linear regulators can achieve output currents
of 3A or higher with proper device selection.
The ISL6521 monitors all the output voltages. The PWM
controller’s adjustable overcurrent function monitors the
output current by using the voltage drop across the upper
MOSFET’s rDS(ON). The linear regulator outputs are
monitored via the FB pins for undervoltage events.
Ordering Information
PKG.
PART NUMBER TEMP. RANGE (°C) PACKAGE DWG. #
ISL6521CBZ
(Note)
0 to 70
16 Ld SOIC M16.15
(Pb-free)
ISL6521CBZ-T
(Note)
0 to 70
16 Ld SOIC M16.15
(Pb-free)
ISL6521IBZ
(Note)
-40 to 85
16 Ld SOIC M16.15
(Pb-free)
ISL6521IBZ-T
(Note)
-40 to 85
16 Ld SOIC M16.15
(Pb-free)
ISL6521EVAL1 Evaluation Board
NOTE: Intersil Pb-free 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-020C.
Features
• Provides 4 Regulated Voltages
- Switching Regulator 20A Capable
- Three Linear Regulators
- Capable of 120mA
- Capable of up to 3A with an External Transistor
• Externally Resistor-Adjustable Outputs
• Simple Single-Loop Control Design
- Voltage-Mode PWM Control
• Fast PWM Converter Transient Response
- High-Bandwidth Error Amplifier
- Full 0% to 100% Duty Ratio
• Excellent Output Voltage Regulation
- All Outputs: 2% Over Temperature
• Overcurrent Fault Monitors
- Switching Regulator Does Not Require Extra Current
Sensing Element, Uses MOSFET’s rDS(ON)
• Small Converter Size
- 300kHz Constant Frequency Operation
- Small External Component Count
• Commercial and Industrial Temperature Range Support
• Pb-free Available (RoHS Compliant)
Applications
FPGA and PowerPC-based boards
• General purpose, low voltage power supplies
Related Literature
• Technical Support Document AG0001, “Power
Management Application Guide for Xilinx FPGAs”
• Technical Support Document AG0002, “Power
Management Application Guide for Altera FPGAs”
• Technical Support Document AG0005, “Power
Management Application Guide for Actel FPGAs”
Pinout
ISL6521 (SOIC)
TOP VIEW
DRIVE2 1
FB2 2
FB 3
COMP 4
GND 5
PHASE 6
BOOT 7
UGATE 8
16 FB3
15 DRIVE3
14 FB4
13 DRIVE4
12 OCSET
11 VCC
10 LGATE
9 PGND
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 LLC. 2004. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.

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Block Diagram
FB3
DRIVE3
DRIVE4
FB4
DRIVE2
FB2
VCC
EA3
-
+
EA4
+-
x 0.70
0.8V
+
-
INHIBIT/SOFT-START
EA2
UV3
+-
UV4
UV2
GND
OSCILLATOR
OCSET
VCC
40A
POWER-ON
RESET (POR)
SOFT-START
AND FAULT
LOGIC
+-
EA1
+-+-
OCC
+-
COMP1
PWM
FB COMP
DRIVE1
GATE
CONTROL
VCC
SYNC
DRIVE
BOOT
UGATE
PHASE
LGATE
PGND

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ISL6521
Typical Applications
High Output Current PWM Converter With Simple Triple Linears Regulators
LIN
+5V
VOUT2
2.5V
120mA
DRIVE2
+
COUT2
Rs2
FB2
Rp2
VOUT3
1.8V
120mA
+ COUT3
DRIVE3
FB3
Rs3
Rp3
VOUT4
3.3V
120mA
+
COUT4
DRIVE4
FB4
Rs4
Rp4
VCC
BOOT
OCSET
CBOOT
ISL6521
UGATE
PHASE
LGATE
PGND
FB
COMP
GND
+ CIN
Q1
LOUT1
VOUT1
1.5V
Q2 CR1
+ COUT1
Rs1
Rp1
High Output Current PWM Converter and Auxiliary 3.3V Linear Regulator
+5V
LIN
VOUT2
2.5V
120mA
DRIVE2
+
COUT2
Rs2
FB2
Rp2
VOUT3
1.8V
120mA
DRIVE3
+
COUT3
Rs3
FB3
Rp3
+5V
VOUT4
3.3V
3A
Q3
DRIVE4
FB4
+
COUT4
Rs4
Rp4
VCC
BOOT
OCSET
CBOOT
ISL6521
UGATE
PHASE
LGATE
PGND
FB
COMP
GND
+ CIN
Q1
LOUT1
VOUT1
1.5V
Q2
CR1
+
COUT1
Rs1
Rp1
3

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ISL6521
Absolute Maximum Ratings
UGATE, BOOT. . . . . . . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to 15V
VCC, PHASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to +7V
DRIVE, LGATE, all other pins . . . . . . . . GND - 0.3V to VCC + 0.3V
Operating Conditions
Supply Voltage on VCC . . . . . . . . . . . . . . . . . . . . . . . . . . +5V 10%
Ambient Temperature Range
ISL6521CBZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to 70°C
ISL6521IBZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40°C to 85°C
Junction Temperature Range. . . . . . . . . . . . . . . . . . -40°C to 125°C
Thermal Information
Thermal Resistance (Typical, Note 1)
JA (°C/W)
SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . .
74
Maximum Junction Temperature (Plastic Package) . . . . . . . 150°C
Maximum Storage Temperature Range . . . . . . . . . . -65°C to 150°C
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300°C
(SOIC - Lead Tips Only)
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.
NOTE:
1. JA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
Electrical Specifications Operating Conditions: VCC = 5V, TA = 0°C to 70°C, Unless Otherwise Noted. Typical specifications are at
TA = 25°C.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN TYP MAX UNITS
VCC SUPPLY CURRENT
Nominal Supply Current
POWER-ON RESET
ICC UGATE, LGATE, and DRIVEx Open
-5-
mA
Rising VCC Threshold
4.25 - 4.51
V
Falling VCC Threshold
3.74 -
4.0
V
OSCILLATOR AND SOFT-START
Free Running Frequency
FOSC
ISL6521CBZ
ISL6521IBZ (-40°C to 85°C)
275 300 325
250 300 350
kHz
kHz
Ramp Amplitude
Soft-Start Interval
REFERENCE VOLTAGE
VOSC
TSS
- 1.5 -
6.25 6.83 7.40
VP-P
ms
Reference Voltage (All Regulators)
All Outputs Voltage Regulation
VREF
ISL6521CBZ
0.780 0.800 0.820
-2.0 - +2.0
V
%
ISL6521IBZ (-40°C to 85°C)
-2.5 - +2.5
%
LINEAR REGULATORS (OUT2, OUT3, AND OUT4)
Output Drive Current (All Linears)
VCC > 4.5V
100 120
-
mA
Undervoltage Level (VFB/VREF)
VUV
SYNCHRONOUS PWM CONTROLLER ERROR AMPLIFIER
- 70 -
%
DC Gain
- 80 -
dB
Gain-Bandwidth Product
GBWP
15 - - MHz
Slew Rate
SR COMP = 10pF
- 6 - V/s
PWM CONTROLLER GATE DRIVERS
UGATE Source
UGATE Sink
LGATE Source
LGATE Sink
PROTECTION
IUGATE
IUGATE
ILGATE
ILGATE
VCC = 5V, VUGATE = 2.5V
VUGATE-PHASE = 2.5V
VCC = 5V, VLGATE = 2.5V
VLGATE = 2.5V
- -1 -
-1-
- -1 -
-2-
A
A
A
A
OCSET Current Source
IOCSET
ISL6521CBZ
ISL6521IBZ (-40°C to 85°C)
34 40
31.5 40
46
48
A
A
4

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ISL6521
Functional Pin Descriptions
VCC (Pin 11)
Provide a well decoupled 5V bias supply for the IC to this
pin. This pin also provides the gate bias charge for the lower
MOSFET controlled by the PWM section of the IC, as well as
the drive current for the linear regulators. The voltage at this
pin is monitored for Power-On Reset (POR) purposes.
GND (Pin 5)
Signal ground for the controller. All voltage levels are
measured with respect to this pin.
PGND (Pin 9)
This is the power ground connection. Tie the source of the
lower MOSFET of the synchronous PWM converter to this
pin.
BOOT (Pin 7)
Floating bootstrap supply pin for the upper gate drive. The
bootstrap capacitor provides the necessary charge to turn
and hold the upper MOSFET on. Connect a suitable
capacitor (0.47F recommended) from this pin to PHASE.
OCSET (Pin 12)
Connect a resistor from this pin to the drain of the upper
PWM MOSFET. This resistor, an internal 40A current
source (typical), and the upper MOSFET’s on-resistance set
the converter overcurrent trip point. An overcurrent trip
cycles the soft-start function.
The voltage at this pin is monitored for power-on reset
(POR) purposes and pulling this pin below 1.25V with an
open drain/collector device will shut down the switching
controller.
PHASE (Pin 6)
Connect this pin to the source of the PWM converter upper
MOSFET. This pin is used to monitor the voltage drop across
the upper MOSFET for overcurrent protection.
UGATE (Pin 8)
Connect UGATE pin to the PWM converter’s upper
MOSFET gate. This pin provides the gate drive for the upper
MOSFET.
LGATE (Pin 10)
This pin provides the gate drive for the synchronous rectifier
lower MOSFET. Connect LGATE to the gate of the lower
MOSFET.
COMP and FB (Pins 4, 3)
COMP and FB are the available external pins of the PWM
converter error amplifier. The FB pin is the inverting input of the
error amplifier. Similarly, the COMP pin is the error amplifier
output. These pins are used to compensate the voltage-mode
control feedback loop of the synchronous PWM converter.
DRIVE2, 3, 4 (Pins 1, 15, 13)
Connect these pins to the point of load or to the base
terminals of external bipolar NPN transistors. These pins are
each capable of providing 120mA of load current or drive
current for the pass transistors.
FB2, 3, 4 (Pins 2, 16, 14)
Connect the output of the corresponding linear regulators to
these pins through properly sized resistor dividers. The
voltage at these pins is regulated to 0.8V. These pins are
also monitored for undervoltage events.
Quickly pulling and holding any of these pins above 1.25V
(using diode-coupled logic devices) shuts off the respective
regulators. Releasing these pins from the pull-up voltage
initiates a soft-start sequence on the respective regulator.
Description
Operation
The ISL6521 monitors and precisely controls one
synchronous PWM converter and three configurable linear
regulators from a +5V bias input. The PWM controller is
designed to regulate the core voltage of an embedded
processor or simple down conversion for high current
applications. The PWM controller drives two MOSFETs (Q1
and Q2) in a synchronous-rectified buck converter
configuration and regulates the output voltage to a level
programmed by a resistor divider. The linear controllers are
designed to regulate three additional system voltages.
Typically, these include any I/O, memory, or clock voltages
that might be required. All three linear controllers support
up to 120mA of load current without external pass devices
or higher currents with external NPN bipolar transistors.
Initialization
The ISL6521 automatically initializes upon receipt of input
power. The Power-On Reset (POR) function continually
monitors the input bias supply voltage. The POR monitors
the bias voltage at the VCC pin. The POR function initiates
soft-start operation after the bias supply voltage exceeds its
POR threshold.
Soft-Start
The POR function initiates the soft-start sequence. The
PWM error amplifier reference input is clamped to a level
proportional to the soft-start voltage. As the soft-start voltage
slews up, the PWM comparator generates PHASE pulses of
increasing width that charge the output capacitor(s).
Similarly, all linear regulators’ reference inputs are clamped
to a voltage proportional to the soft-start voltage. The ramp-
up of the internal soft-start function provides a controlled
output voltage rise.
Figure 1 shows the soft-start sequence for a typical
application. At T0 the +5V bias voltage starts to ramp up
crossing the 4.5V POR threshold at time T1. On the PWM
section, the oscillator’s triangular waveform is compared to
5