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DATASHEET
Dual (180°Out-of-Phase) PWM and Linear Controller
ISL6446A
The ISL6446A is a high-performance, triple output controller
that provides a single high-frequency power solution primarily
for Broadband, DSL and Networking applications. This device
integrates complete control, monitoring and protection
functions for two synchronous buck PWM controllers and one
linear controller. Input voltage ripple and total RMS input
current is substantially reduced by synchronized 180°
out-of-phase operation of the two PWMs.
The two PWM buck converters provide simple voltage mode
control. The output voltage of the converters can be precisely
regulated to as low as 0.6V, with a maximum tolerance of
±1.5% over-temperature and line variations. Programmable
switching frequency down to 100kHz provides optimized low
cost solution for ATX power supplies. It is also able to operate
up to 2.5MHz to deliver compact solutions. The linear
controller provides a low-current output.
Each PWM controller has soft-start and independent enable
functions combined on a single pin. A capacitor from SS/EN to
ground sets the soft-start time; pulling SS/EN pin below 1V
disables the controller. Both outputs can soft-start into a
prebiased load.
The ISL6446A incorporates robust protection features. An
adjustable overcurrent protection circuit monitors the output
current by sensing the voltage drop across the upper MOSFET
rDS(ON). Latch-off mode overcurrent operation protects the
DC/DC converters from damage under overload and
short-circuit conditions. A PGOOD signal is issued when
soft-start is complete and PWM outputs are within 10% of
their regulated values and the linear regulator output is higher
than 75% of its nominal value. Thermal shutdown circuitry
turns the device off if the IC temperature exceeds +150°C.
Features
• 4.5V to 5.5V or 5.5V to 24V input voltage range
• Three programmable power output voltages
- Two PWM controllers with out-of-phase operation
- Voltage-mode PWM control
- One linear controller
• Programmable switching frequency from 100kHz to 2.5MHz
• Fast transient response
- High-bandwidth error amplifier
• Extensive circuit protection functions
- Undervoltage, and over-temperature
- Overvoltage with latch-off mode
- Programmable overcurrent limit with latch-off mode
- Lossless current sensing (no sense resistor needed)
• Externally adjustable soft-start time
- Independent enable control
- Voltage tracking capability
- Able to soft-start into a prebiased load
• PGOOD output with delay
Applications
• ATX power supplies
• DSP, ASIC, and FPGA point-of-load regulation
• Industrial and security networking applications
VOUT1
VOUT2
Feedback
and
Compensation
Network
R1
Feedback
and
Compensation
Network
R2
VCC VIN
CVCC
ROCSET1
VCC
COMP1
FB1
VIN
OCSET1 CBOOT1
BOOT1
UGATE1
VIN1 = VIN
COCSET1
CIN1
Q1
COMP2
FB2
PHASE1
LGATE1
L1
Q2
VOUT1
COUT1
ISL6446A
ROCSET2
OCSET2 CBOOT2
BOOT2
VIN2 = VIN
COCSET2
CIN2
PGOOD
RT
SS/EN1
SS/EN2
UGATE2
PHASE2
LGATE2
LCDR
LCFB
Q3
L2
Q4
VOUT2
COUT2
SGND PGND
FIGURE 1. TYPICAL APPLICATION
100
98
96
94
92
90 VOUT = 3.3V
VOUT = 5V
88
86
84
82
80 0 5 10 15 20
LOAD CURRENT (A)
FIGURE 2. EFFICIENCY vs LOAD CURRENT (OBTAINED FROM
ISL6446AEVAL1Z)
25
August 27, 2015
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CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas LLC 2012, 2013, 2015. 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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Pin Configuration
ISL6446A
ISL6446A
(24 LD QSOP)
TOP VIEWI
OCSET1 1
SS1/EN1 2
COMP1 3
FB1 4
RT 5
SGND 6
LCDR 7
LCFB 8
FB2 9
COMP2 10
SS2/EN2 11
OCSET2 12
24 VIN
23 BOOT1
22 UGATE1
21 PHASE1
20 LGATE1
19 VCC
18 PGND
17 LGATE2
16 PHASE2
15 UGATE2
14 BOOT2
13 PGOOD
Pin Descriptions
PIN
NAME
PIN #
DESCRIPTION
BOOT1, 2 23, 14 These pins power the upper MOSFET drivers of each PWM converter. The anode of each internal bootstrap diode is connected
to the VCC pin. The cathode of the bootstrap diode is connected to this pin, which should also connect to the bootstrap capacitor.
UGATE1, 2 22, 15 These pins provide the gate drive for upper MOSFETs, bootstrap from the VCC pin.
PHASE1, 2 21, 16 These are the junction points of the upper MOSFET sources, output filter inductor and lower MOSFET drains. Connect these pins
accordingly to the respective converter.
LGATE1, 2 20, 17 These are the outputs of the lower N-channel MOSFET drivers, sourced from the VCC pin.
PGND
18 This pin provides the power ground connection for the lower gate drivers. This pin should be connected to the source of the lower
MOSFET for PWM1 and PWM2 and the negative terminals of the external input capacitors.
FB1, 2
4, 9 These pins are connected to the feedback resistor divider and provide the voltage feedback signals for the respective controller. They
set the output voltage of the converter. In addition, the PGOOD circuit and OVP circuit use these inputs to monitor the output voltage
status.
COMP1, 2 3, 10 These pins are the error amplifier outputs for the respective PWM. They are used, along with the FB pins, as the compensation point
for the PWM error amplifier.
PGOOD
13 This is an open-drain logic output used to indicate the status of the output voltages. This pin is pulled low when either of the two
PWM outputs is not within 10% of the respective nominal voltage or when the linear output drops below 75% of its nominal voltage.
To maintain the PGOOD function if the linear output is not used, connect the LCFB to VCC.
SGND
6 This is the signal ground, common to both controllers, and must be routed separately from the high current grounds (PGND). All
voltage levels are measured with respect to this pin.
VIN 24 This pin powers the controllers with an internal linear regulator (if VIN > 5.5V) and must be closely decoupled to ground using a
ceramic capacitor as close to the VIN pin as possible. VIN is also the input voltage applied to the upper FET of both converters.
TABLE 1. INPUT SUPPLY CONFIGURATION
INPUT
PIN CONFIGURATION
5.5V to 24V
Connect the input supply to the VIN pin. The VCC
pin will provide a 5V output from the internal
voltage regulator.
5V ±10%
Connect the input supply to the VCC pin.
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ISL6446A
Pin Descriptions (Continued)
PIN
NAME
VCC
RT
SS1/EN1
SS2/EN2
LCFB
LCDR
OCSET1, 2
PIN #
19
5
2, 11
8
7
1, 12
DESCRIPTION
This pin supplies the bias for the regulators, powers the low-side gate drivers and external boot circuitry for high-side gate drivers.
The IC may be powered directly from a single 5V (±10%) supply at this pin; when used as a 5V supply input, this pin must be
externally connected to VIN. When VIN > 5.5, VCC is the output of the internal 5V linear regulator output. The VCC pin must always
be decoupled to power ground with a minimum of 1µF ceramic capacitor, placed very close to the pin.
This is the operating frequency adjustment pin. By placing a resistor from this pin to SGND, the oscillator frequency can be
programmed from 100kHz to 2.5MHz.
These pins provide enable/disable and soft-start function for their respective controllers. The output is held off when the pin is
pulled to ground. When the chip is enabled, the regulated 30µA pull-up current source charges the capacitor connected from the
pin to ground. The output voltage of the converter follows the ramping voltage on the SS/EN pin. See “Soft-start and Voltage
Tracking” on page 12 for more details.
This pin is the feedback pin for the linear controller. An external voltage divider network connected to this pin sets the output
voltage of the linear controller. If the linear controller is not used, tie this pin to VCC.
Open drain output PNP Transistor or P-channel MOSFET Driver. LCDR connects to the base of an external PNP pass transistor or
the gate of the MOSFET to form a positive linear regulator. A small resistor can be inserted between the LCDR and the base of
the PNP pass transistor or the gate of the MOSFET to alleviate thermal stress at output short condition.
These pins are the overcurrent set points for the respective PWM controllers. Connect a resistor (ROCSET) from this pin to the
drain of the upper MOSFET. ROCSET, an internal 110µA current source, and the upper MOSFET ON-resistance rDS(ON) set the
converter overcurrent (OC) trip point according to Equation 1:
IOC = I--O-----C----S----rE--D--T--S------O-R----NO-----C----S----E----T--
(EQ. 1)
IOC includes the DC load current, as well as the ripple current. An overcurrent trip initiates hiccup mode.
The voltage on the OCSET pin should not exceed 0.7V above the VIN pin voltage for proper current sensing when the UGATE is
turned on.
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
PART
MARKING
TEMPERATURE RANGE
(°C)
PACKAGE
(RoHS Compliant)
PKG.
DWG. #
ISL6446AIAZ
ISL6446 AIAZ
-40 to +85
24 Ld QSOP
M24.15
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 ISL6446A. For more information on MSL please see tech brief TB363.
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Block Diagram
REFERENCE
BIAS CURRENT
30µA 100µA 0.6V
ISL6446A
VCC
VCC
POWER ON
RESET
AND CONTROL
VIN
5V LINEAR
REGULATOR
COMP1
FB1
SS1/EN1
SS2/EN2
FB2
COMP2
0.6V
VCC5
VCC5
30µA
30µA
0.6V
FAULT1
UVP1
OVP1
PG1
EN1
SS1
STARTUP
SS1 EN1
SS2 EN2
FAULT2
UVP2
OVP2
PG2
EN2
SS2
RT
PGOOD
PG1
PG2
PG3
PWM1
RAMP1
CLOCK AND
SAWTOOTH
GENERATOR
RAMP2
180°
PWM2
110µA
OCSET1
VCC
UVP1
OVP1
PG1
EN1
OUTPUT1
DRIVERS
GATE CONTROL
LOGIC VCC
DEAD-TIME
CONTROL
OVERCURRENT
PGND
BOOT1
UGATE1
PHASE1
LGATE1
110µA
VCC
UVP2
OVP2
PG2
EN2
OUTPUT2
DRIVERS
GATE CONTROL
LOGIC VCC
DEAD-TIME
CONTROL
OVERCURRENT
PGND
FAULT3
PG3 LCFB
OCSET2
BOOT2
UGATE2
PHASE2
LGATE2
gm*VE
0.6V
LCFB
LCDR
SGND
FIGURE 3. BLOCK DIAGRAM
PGND
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ISL6446A
Typical Application Schematic
VOLTAGE INPUTS REQUIRED
VIN (4.5V TO 24V) = VIN1 = VIN2
VCC (5V; INTERNAL IF VIN > 5.6V)
VIN3 (VCC) FOR LINEAR
TYPE-3 COMPENSATION SHOWN
C102
VOUT1
R102
R101
C101
R103
C103
C202
R100
VOUT2
R202
R201
C201
R203 C203
R200
TYPE-3 COMPENSATION SHOWN
VCC
RPGOOD
CSS1/EN1 CSS2/EN2 RRT
VCC
VCC
CVCC CVIN
VIN
OPTIONAL
CONNECTION
(FOR VIN = VCC = 5V)
ROCSET1
VIN
VIN1 = VIN
COMP1
FB1
OCSET1
BOOT1
COCSET1
CBOOT1
Q101
CIN1
UGATE1
PHASE1
0.9µH
L100
VOUT1
COMP2
FB2
PGOOD
RT
SS1/EN1
SS2/EN2
ISL6446A
LGATE1
Q102
2x680µF/18m
2x100µF
1x47µF
ROCSET2
VIN2 = VIN
COUT1
OCSET2
BOOT2
UGATE2
PHASE2
LGATE2
COCSET2
CBOOT2
Q201
CIN2
0.9µH
L200
Q202
LCDR
R303
R304
C301 R302
Q301
VOUT2
COUT2
2x680µF/18m
2x100µF
VIN3
CIN3
SGND
PGND
LCFB
R300
R301
VOUT3
COUT3
FIGURE 4. ISL6446A TYPICAL APPLICATION
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