Data Sheet No. PD94252
IRU3047
DUAL SYNCHRONOUS PWM CONTROLLER WITH
CURRENT SHARING CIRCUITRY AND LDO CONTROLLER
PRELIMINARY DATA SHEET
FEATURES
Dual Synchronous Controller in 20-Pin Package
with 1808 out-of-phase operation
LDO Controller with 40mA drive
Can be configured as 2-Independent or 2-Phase
PWM Controller
Programmable Current Sharing in 2-Phase Configu-
ration
Flexible, Same or Separate Supply Operation
Operation from 4V to 25V Input
Internal 200KHz Oscillator per phase
Soft-Start controls all outputs
Fixed Frequency Voltage Mode
500mA Peak Output Drive Capability
Short Circuit Protection for All Outputs
Power Good Output
DESCRIPTION
The IRU3047 IC combines a Dual synchronous Buck
controller and a linear regulator controller, providing a
cost-effective, high performance and flexible solution for
multi-output applications. The Dual synchronous con-
troller can be configured as 2-independent or 2-phase
controller. In 2-phase configuration, the IRU3047 provides
a programmable current sharing which is ideal when the
output power exceeds any single input power budget.
IRU3047 provides a separate adjustable output by driv-
ing a switch as a linear regulator. This device features an
internal 200KHz oscillator, under-voltage lockout for all
input supplies, an external programmable soft-start func-
tion as well as output under-voltage detection that latches
off the device when an output short is detected.
APPLICATIONS
Dual-Phase Power Supply
DDR Memory Source Sink Vtt Application
Graphic Card
Hard Disk Drive
Power supplies requiring multiple outputs
TYPICAL APPLICATION
12V
L1
5V
C1
C2
C3
C4
V
CL
Vcc
C5
3.3V
C6
V
OUT2
C7
R2
C8
C9
R3
R4
Comp2
HDrv2
Comp1
Q1
R1
Fb3
V
OUT3
LDrv1
Q3
VcH1
VcH2
HDrv1
Q2
C13
C12
L2
D1
D2
C11
C14
L3
R5
V
OUT1
C16
U1
IRU3047
PGnd
V
REF
Vp2
Fb1
Fb2
C17
Q4
L4
R9
R7
R8
PGood
C10
PGood
SS
LDrv2
Gnd
Q5
Figure 1 - Typical application of IRU3047 configured as 2-phase converter.
PACKAGE ORDER INFORMATION
T
A
(°C)
0 To 70
Rev. 1.0
09/09/02
DEVICE
IRU3047CW
PACKAGE
20-Pin Plastic SOIC (W)
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1
IRU3047
ABSOLUTE MAXIMUM RATINGS
Vcc Supply Voltage .................................................. 25V
V
C
H1, V
C
H2 and V
CL
Supply Voltage ........................... 30V (not rated for inductive load)
Storage Temperature Range ...................................... -65°C To 150°C
Operating Junction Temperature Range .....................
0°C To 125°C
PACKAGE INFORMATION
20-PIN PLASTIC SOIC WB (W)
TOP VIEW
V
REF
1
Vp2 2
Fb2 3
Vcc 4
Comp1 5
Comp2 6
VcH2 7
HDrv2 8
LDrv2 9
PGnd 10
20 Gnd
19 P G o o d
18 Fb1
17 SS
16 Fb3
15 V
OUT3
14 VcH1
13 HDrv1
12 LDrv1
11 V
CL
u
JA
=758C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc=5V, VcH1=VcH2=V
CL
=12V and T
A
=0 to 70°C.
Typical values refer to T
A
=25°C. Low duty cycle pulse testing is used which keeps junction and case temperatures
equal to the ambient temperature.
PARAMETER
Reference Voltage Section
Fb Voltage
Fb Voltage Line Regulation
UVLO Section
UVLO Threshold - Vcc
UVLO Hysteresis - Vcc
UVLO Threshold - VccLDO
UVLO Hysteresis - VccLDO
UVLO Threshold - VcH1
UVLO Hysteresis - VcH1
UVLO Threshold - VcH2
UVLO Hysteresis - VcH2
UVLO Threshold - Fb
UVLO Hysteresis - Fb
Supply Current Section
Vcc Dynamic Supply Current
VcH1 Dynamic Supply Current
VcH2 Dynamic Supply Current
Vcc Static Supply Current
VcH1 Static Supply Current
VcH2 Static Supply Current
SYM
V
FB
L
REG
UVLO
V
CC
TEST CONDITION
MIN
1.225
5<Vcc<12
Supply Ramping Up
TYP
1.250
0.2
4.2
0.25
4.2
0.25
3.5
0.2
3.5
0.2
0.6
0.1
5
7
7
3.5
2
2
MAX UNITS
1.275
V
%
V
V
V
V
V
V
V
V
V
V
mA
mA
mA
mA
mA
mA
UVLO
V
CC
LDO
Supply Ramping Up
UVLO
V
C
H1
Supply Ramping Up
UVLO
V
C
H2
Supply Ramping Up
UVLO
Fb
Fb Ramping Down
Dyn I
CC
Dyn I
C
H1
Dyn I
C
H2
I
CCQ
I
C
H1Q
I
C
H2Q
Freq=200KHz, C
L
=1500pF
Freq=200KHz, C
L
=1500pF
Freq=200KHz, C
L
=1500pF
SS=0V
SS=0V
SS=0V
2
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Rev. 1.0
09/09/02
IRU3047
PARAMETER
Soft-Start Section
Charge Current
Power Good Section
Fb1 Lower Trip Point
Fb1 Upper Trip Point
Fb2 Lower Trip Point
Fb2 Upper Trip Point
Fb3 Lower Trip Point
Fb3 Upper Trip Point
Power Good Voltage OK
Error Amp Section
Fb Voltage Input Bias Current
Fb Voltage Input Bias Current
Transconductance 1
Transconductance 2
Input Offset Voltage for PWM2
Oscillator Section
Frequency
Ramp Amplitude
Output Drivers Section
Rise Time
Fall Time
Dead Band Time
Max Duty Cycle
Min Duty Cycle
LDO Controller Section
Drive Current
Fb Voltage
Input Bias Current
SYM
SS
IB
PG
FB1L
PG
FB1H
PG
FB2L
PG
FB2H
PG
FB3L
PG
FB3H
V
PG
I
FB1
I
FB2
g
m1
g
m2
V
OS(ERR)2
Freq
V
RAMP
Tr
Tf
T
DB
T
ON
T
OFF
I
LDO
V
FB
LDO
I
LDO(BIAS)
TEST CONDITION
SS=0V
Fb1 Ramping Down
Fb1 Ramping Up
Fb2 Ramping Down
Fb2 Ramping Up
Fb3 Ramping Down
Fb3 Ramping Up
5K resistor pulled up to 5V
SS=3V
SS=0V
MIN
15
TYP
25
0.9
V
REF
1.1
V
REF
0.9
V
REF
1.1
V
REF
0.9
V
REF
1.1
V
REF
4.8
-0.1
-64
400
600
0
200
1.25
35
50
150
90
0
45
1.25
0.5
MAX
30
UNITS
mA
V
V
V
V
V
V
V
mA
mA
mmho
mmho
mV
KHz
V
ns
ns
ns
%
%
mA
V
mA
4.5
5
Fb2 to V
P2
Rt=Open
-2
180
+2
220
C
L
=1500pF
C
L
=1500pF
Fb=1V, Freq=200KHz
Fb=1.5V
50
85
0
30
1.225
100
100
250
1.275
2
PIN DESCRIPTIONS
PIN#
1
2
PIN SYMBOL
V
REF
Vp2
PIN DESCRIPTION
Reference Voltage.
Non-inverting input to the second error amplifier, in the current sharing mode it is con-
nected to the programming resistor. In independent two channel mode it is connected to
the reference voltage (Pin1) when Fb2 is connected to the resistor divider to set the
output voltage.
Inverting inputs to the error amplifiers, in current sharing mode Fb1 is connected to a
resistor divider to set the output voltage and Fb2 is connected to programming resistor to
achieve current sharing. In independent two channel mode, these pins work as feedback
inputs for each channel.
Supply voltage for the internal blocks of the IC.
Compensation pins for the error amplifiers.
Supply voltage for the high side output drivers. These are connected to voltages that
must be at least 4V higher than their bus voltages (assuming 5V threshold MOSFET). A
minimum of 1mF high frequency capacitor must be connected from these pins to PGnd
pin to provide peak drive current capability.
Output driver for high side power MOSFET. Connect a diode, such as BAT54 or 1N4148,
from these pins to ground for the application when the inductor current goes negative
(Source/Sink), soft-start at no load and for fast load transient from full load to no load.
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3,18
Fb2, Fb1
4
Vcc
5,6 Comp1, Comp2
7,14
VcH2, VcH1
8,13
HDrv2, HDrv1
Rev. 1.0
09/09/02
3
IRU3047
PIN#
9,12
10
11
15
16
17
19
20
PIN SYMBOL
LDrv2, LDrv1
PGnd
V
CL
V
OUT3
Fb3
SS
PGood
Gnd
PIN DESCRIPTION
Output driver for the synchronous power MOSFET.
This pin serves as the separate ground for MOSFET’s driver and should be connected to
the system’s ground plane.
Supply voltage for the low side output drivers.
Driver signal for the LDO’s external transistor.
LDO’s feedback pin, connected to a resistor divider to set the output voltage of LDO.
Soft-Start pin. The converter can be shutdown by pulling this pin below 0.5V.
Power Good pin. This pin is a collector output that switches Low when any of the outputs
are outside of the specified under voltage trip point.
Ground pin.
BLOCK DIAGRAM
Vcc
4
Bias
Generator
64uA Max
4.2V / 4.0V
3V
1.25V
POR
14 V c H 1
25uA
13 HDrv1
SS 17
UVLO
VcH1
VcH2
3.5V / 3.3V
3.5V / 3.3V
11 V
CL
POR
PWM Comp1
Error Amp1
1.25V
25K
12 LDrv1
R
25K
Fb1 18
S
Comp1
Q
Reset Dom
5
Ramp1
Two Phase
Oscillator
Ramp2
Set1
SS > 2V
7 VcH2
8 HDrv2
Set2
V
REF
1
1.25V
S
PWM Comp2
25K
Error Amp2
Q
R
Reset Dom
Vp2
2
25K
9 LDrv2
Fb2
3
0.5V
10 PGnd
POR
Comp2
6
Fb2 Monitor
Shut Down
Vcc
25K
1.25V
Fb1
Fb2
Fb3
PGood
19 PGood
15 V
OUT3
Fb3 16
Gnd 20
25K
2V
40mA LDO Controller
SS
Figure 2 - Block diagram of the IRU3047.
4
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Rev. 1.0
09/09/02
IRU3047
THEORY OF OPERATION
Introduction
The IRU3047 is designed for multi-outputs applications.
It includes two synchronous buck controllers and a lin-
ear regulator controller. The two synchronous controller
operates with fixed frequency voltage mode and can be
configured as two independent controller or 2-phase con-
troller with current sharing. The timing of the IC is pro-
vided through an internal oscillator circuit. These are two
out of phase oscillators with 200KHz switching frequency.
Independent Mode
In this mode the IRU3047 provides two independent out-
puts with either common or different input voltages. The
output voltage of the individual channel is set and con-
trolled by the output of the error amplifier, this is the
amplified error signal from the sensed output voltage and
the reference voltage. This voltage is compared to the
ramp signal and generates fixed frequency pulses of vari-
able duty-cycle, which drives the two N-channel exter-
nal MOSFETs.
Current Sharing Mode
In the current sharing mode, the two converter’s outputs
tied together and provide one single output (see Figure
1). In this mode, one control loop acts as a master and
sets the output voltage as a regular Voltage Mode buck
controller and the other control loop acts as a slave and
monitors the current information for current sharing. The
current sharing is programmable and sets by using two
external resistors in output currents’ path. The slave's
error amplifier, error amplifier 2 (see the block diagram)
measures the voltage drops across the current sense
resistors, the differential of these signals is amplified
and compared with the ramp signal and generate the
fixed frequency pulses of variable duty cycle to match
the output currents.
Out of Phase Operation
The IRU3047 drives its two output stages 180
o
out of
phase. In 2-phase configuration, the two inductor ripple
currents cancel each other and result to a reduction of
the output current ripple and contributes to a smaller
output capacitors for the same ripple voltage require-
ment.
In application with single input voltage, the 2-phase con-
figuration reduces the input ripple current. This results in
much smaller RMS current in the input capacitor and
reduction of input capacitor.
Soft-Start
The IRU3047 has a programmable soft start to control
the output voltage rise and limit the current surge at the
start-up. To ensure correct start-up, the soft-start se-
quence initiates when the Vcc, VcH1 and VcH2 rise
above their threshold and generates the Power On Re-
set (POR) signal. Soft-start function operates by sourc-
ing an internal current to charge an external capacitor to
about 3V. Initially, the soft-start function clamps the E/
A’s output of the PWM converter. As the charging volt-
age of the external capacitor ramps up, the PWM sig-
nals increase from zero to the point the feedback loop
takes control.
Shutdown
The converter can be shutdown by pulling the soft-start
pin below 0.5V. This can be easily done by using an
external small signal transistor. During shutdown the
MOSFET drivers and the LDO controller turn off.
Power Good
The IRU3047 provides a power good signal. This is an
open collector output and it is pulled low if the output
voltages are not within the specified threshold. This pin
can be left floating if not used.
Short-Circuit Protection
The outputs are protected against the short circuit. The
IRU3047 protects the circuit for shorted output by sens-
ing the output voltages. The IRU3047 shuts down the
PWM signals and LDO controller, when the output volt-
ages drops below the set values.
Under-Voltage Lockout
The under-voltage lockout circuit assures that the
MOSFET driver outputs and LDO controller remain in
the off state whenever the supply voltages drop below
set parameters. Normal operation resumes once the
supply voltages rise above the set values.
Rev. 1.0
09/09/02
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