DATASHEET
ISL6446
Dual (180°Out-of-Phase) PWM and Linear Controller
The
ISL6446
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’s 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 ISL6446 incorporates robust protection features. An
adjustable overcurrent protection circuit monitors the output
current by sensing the voltage drop across the upper MOSFET
r
DS(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.
FN7944
Rev 2.00
October 12, 2015
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
VCC
C
VCC
Feedback
and
Compensation
Network
R
1
VOUT2
Feedback
and
Compensation
Network
R
2
COMP2
FB2
VCC
COMP1
FB1
VIN
R
OCSET1
100
98
96
94
EFFICIENCY (%)
92
90
88
86
84
82
80
0
5
10
15
20
25
V
OUT
= 3.3V
V
OUT
= 5V
VOUT1
VIN1 = VIN
VIN
C
OCSET1
OCSET1
C
BOOT1
BOOT1
Q
1
C
IN1
UGATE1
VOUT1
PHASE1
L
1
LGATE1
C
OUT1
Q
2
R
OCSET2
VIN2 = VIN
C
OCSET2
C
IN2
L
2
Q
4
VOUT2
C
OUT2
ISL6446
OCSET2
C
BOOT2
BOOT2
Q
3
UGATE2
PHASE2
LGATE2
PGOOD
RT
SS1/EN1
SS2/EN2
SGND
LCDR
LCFB
PGND
LOAD CURRENT (A)
FIGURE 1. TYPICAL APPLICATION
FIGURE 2. EFFICIENCY vs LOAD CURRENT (OBTAINED FROM
ISL6446EVAL1Z)
FN7944 Rev 2.00
October 12, 2015
Page 1 of 19
ISL6446
Pin Configuration
ISL6446
(24 LD QSOP)
TOP VIEW
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
SYMBOL
BOOT2, 1
UGATE2, 1
PHASE2, 1
LGATE2, 1
PGND
FB1, 2
PIN #
DESCRIPTION
14, 23 These pins power are 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.
15, 22 These pins provide the gate drive for upper MOSFETs, bootstrapped from the VCC pin.
16, 21 These are the junction points of the upper MOSFET sources, the output filter inductor and lower MOSFET drains. Connect these
pins accordingly to the respective converter.
17, 20 These are the outputs of the lower N-Channel MOSFET drivers, sourced from the VCC pin.
18
4, 9
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.
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.
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.
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 LCFB to VCC.
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.
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. The VIN is the input voltage applied to the upper FET of both converters.
TABLE 1. INPUT SUPPLY CONFIGURATION
INPUT
5.5V to 24V
PIN CONFIGURATION
Connect the input supply to the VIN pin. The VCC
pin will provide a 5V output from the internal
voltage regulator.
Connect the input supply to the VCC pin.
COMP1, 2
PGOOD
3, 10
13
SGND
VIN
6
24
5V ±10%
VCC
19
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.
FN7944 Rev 2.00
October 12, 2015
Page 2 of 19
ISL6446
Pin Descriptions
SYMBOL
RT
SS1/EN1
SS2/EN2
PIN #
5
2, 11
(Continued)
DESCRIPTION
This is the operating frequency adjustment pin. By placing a resistor from this pin to the 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 11
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. The 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 (R
OCSET
) from this pin to the
drain of the upper MOSFET. R
OCSET
, an internal 110µA current source, and the upper MOSFET ON-resistance r
DS(ON)
set the
converter overcurrent (OC) trip point according to
Equation 1:
I
OCSET
R
OCSET
-
I
OC
= --------------------------------------------------
r
DS
ON
(EQ. 1)
LCFB
LCDR
8
7
OCSET1, 2
1, 12
I
OC
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)
ISL6446IAZ
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
ISL6446.
For more information on MSL please see tech brief
TB363.
PART
MARKING
ISL 6446IAZ
TEMP
RANGE (°C)
-40 to +85
PACKAGE
(RoHS Compliant)
24 Ld QSOP
PKG.
DWG. #
M24.15
FN7944 Rev 2.00
October 12, 2015
Page 3 of 19
ISL6446
Block Diagram
VCC
VIN
VCC
REFERENCE
BIAS CURRENT
30µA 100µA 0.6V
POWER-ON
RESET
AND CONTROL
5V LINEAR
REGULATOR
110µA
OCSET1
VCC
UVP1
OVP1
PG1
EN1
OUTPUT1
DRIVERS
BOOT1
COMP1
UGATE1
FB1
0.6V
-
+
FAULT1
UVP1
OVP1
PG1
EN1
+
-
PWM1
GATE CONTROL
LOGIC
VCC
DEAD TIME
CONTROL
OVERCURRENT
PGND
PHASE1
LGATE1
VCC5
30µA
VCC5
30µA
SS1
RAMP1
0°
CLOCK AND
SAWTOOTH
GENERATOR
UVP2
OVP2
PG2
EN2
OUTPUT2
DRIVERS
PWM2
GATE CONTROL
LOGIC
VCC
DEAD TIME
CONTROL
OVERCURRENT
PGND
FAULT3
PHASE2
110µA
OCSET2
STARTUP
SS1/EN1
SS1
EN1
VCC
SS2/EN2
SS2
EN2
BOOT2
FAULT2
UVP2
OVP2
PG2
EN2
SS2
0.6V
+
FB2
RAMP2
180°
UGATE2
-
+
-
LGATE2
COMP2
PG3 LCFB
RT
PGOOD
PG1
PG2
PG3
-
g
m
*V
E
0.6V
LCFB
+
LCDR
SGND
PGND
FIGURE 3. BLOCK DIAGRAM
FN7944 Rev 2.00
October 12, 2015
Page 4 of 19
ISL6446
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
C
102
VCC
R
102
VOUT1
R
101
FB1
R
103
C
103
C
202
UGATE1
PHASE1
COMP2
C
201
LGATE1
Q
102
FB2
2x680µF/18m
2x100µF
1x47µF
VIN2 = VIN
C
101
COMP1
VIN
OCSET1
BOOT1
C
VCC
C
VIN
VCC
VIN
OPTIONAL
CONNECTION
(FOR VIN = VCC = 5V)
R
OCSET1
VIN1 = VIN
C
OCSET1
C
BOOT1
Q
101
C
IN1
R
100
0.9µH
L
100
VOUT1
R
202
VOUT2
R
201
C
OUT1
R
OCSET2
R
203
C
203
R
200
ISL6446
OCSET2
C
OCSET2
TYPE-3 COMPENSATION SHOWN
BOOT2
C
BOOT2
Q
201
C
IN2
UGATE2
VCC
PHASE2
R
PGOOD
LGATE2
Q
202
0.9µH
L
200
VOUT2
C
OUT2
2x680µF/18m
2x100µF
PGOOD
RT
SS1/EN1
SS2/EN2
LCDR
R
303
C
301
R
304
VIN3
R
302
Q
301
LCFB
VOUT3
R
300
R
301
C
OUT3
C
IN3
C
SS1/EN1
C
SS2/EN2
R
RT
SGND
PGND
FIGURE 4. ISL6446 TYPICAL APPLICATION
FN7944 Rev 2.00
October 12, 2015
Page 5 of 19
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