Data Sheet No. PD94251
IRU3046
DUAL SYNCHRONOUS PWM CONTROLLER WITH
CURRENT SHARING CIRCUITRY AND LDO CONTROLLER
PRELIMINARY DATA SHEET
FEATURES
Dual Synchronous Controller in 24-Pin Package
with 1808 out-of-phase operation
LDO Controller with Independent Bias Supply
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
Programmable Switching Frequency up to 400KHz
Soft-Start controls all outputs
Precision Reference Voltage Available
500mA Peak Output Drive Capability
Short Circuit Protection for all outputs
Power Good Output
Synchronizable with External Clock
DESCRIPTION
The IRU3046 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 IRU3046 provides
a programmable current sharing which is ideal when the
output power exceeds any single input power budget.
IRU3046 provides a separate adjustable output by driv-
ing a switch as a linear regulator. This device features
programmable switching frequency up to 400KHz per
phase, under-voltage lockout for all input supplies, an
external programmable soft-start function as well as out-
put 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
C5
3.3V
C6
V
OUT2
C7
R2
C8
C9
R3
R4
Comp2
HDrv2
Q1
R1
Vcc
VccLDO
V
SEN33
V
OUT3
Fb3
IRU3046
Rt
Sync
Comp1
VcH1
VcH2
HDrv1
Q2
C13
C12
L2
D1
D2
C11
C14
L3
R5
V
OUT1
C16
LDrv1
Q3
C15
R6
U1
PGnd
V
REF
Vp2
Fb1
Fb2
Q4
C17
R7
R8
L4
R9
PGood
C10
PGood
SS
LDrv2
Gnd
Q5
C18
R10
Figure 1 - Typical application of IRU3046 configured as 2-phase converter with current sharing.
PACKAGE ORDER INFORMATION
T
A
(°C)
0 To 70
Rev. 1.9
09/27/02
DEVICE
IRU3046CF
PACKAGE
24-Pin Plastic TSSOP (F)
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FREQUENCY
200-400KHz
1
IRU3046
ABSOLUTE MAXIMUM RATINGS
Vcc Supply Voltage ..................................................
VccLDO, VcH1, VcH2 and V
CL
Supply Voltage ...........
Storage Temperature Range ......................................
Operating Junction Temperature Range .....................
25V
30V (not rated for inductive load)
-65°C To 150°C
0°C To 125°C
PACKAGE INFORMATION
24-PIN PLASTIC TSSOP (F)
TOP VIEW
V
REF 1
Vp2
2
Fb2
3
Vcc
4
Comp1
5
Comp2
6
Rt
7
Sync
8
VcH2
9
HDrv2
10
LDrv2
11
PGnd
12
24
Gnd
23
PGood
22
V
SEN33
21
Fb1
20
SS
19
Fb3
18
V
OUT3
17
VccLDO
16
VcH1
15
HDrv1
14
LDrv1
13
V
CL
θ
JA
= 84°C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc=5V, VcH1=VcH2=V
CL
=VccLDO=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 tem-
peratures 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
UVLO Threshold - V
SEN33
UVLO Hysteresis - V
SEN33
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
VccLDO Static Supply Current
SYM
V
FB
L
REG
TEST CONDITION
MIN
1.225
5<Vcc<12
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
2.5
0.2
5
7
7
3.5
2
2
1
MAX UNITS
1.275
V
%
V
V
V
V
V
V
V
V
V
V
V
V
mA
mA
mA
mA
mA
mA
mA
Rev. 1.9
09/27/02
UVLO
V
CC
Supply Ramping Up
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
UVLO
V
SEN33
Supply Ramping Up
Dyn I
CC
Dyn I
C
H1
Dyn I
C
H2
I
CCQ
I
C
H1Q
I
C
H2Q
I
C
LDO
Freq=200KHz, C
L
=1500pF
Freq=200KHz, C
L
=1500pF
Freq=200KHz, C
L
=1500pF
SS=0V
SS=0V
SS=0V
SS=0V
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2
IRU3046
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)
C
L
=1500pF
C
L
=1500pF
Fb=1V, Freq=200KHz
Fb=1.5V
50
85
0
30
1.225
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
350
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
100
100
250
ns
ns
ns
%
%
mA
V
mA
4.5
5
Fb2 to V
P2
Rt=Open
Rt=Gnd
-2
180
300
+2
220
450
1.275
2
PIN DESCRIPTIONS
PIN#
1
2
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 2-channel mode it is connected to
V
REF
pin when Fb2 is connected to the resistor divider to set the output voltage.
Fb2
Inverting inputs to the error amplifiers. In current sharing mode, Fb1 is connected to a
Fb1
resistor divider to set the output voltage and Fb2 is connected to programming resistor to
achieve current sharing. In independent 2-channel mode, these pins work as feedback
inputs for each channel.
Vcc
Supply voltage for the internal blocks of the IC.
Comp1, Comp2 Compensation pins for the error amplifiers.
Rt
The switching frequency can be programmed between 200KHz and 400KHz by connect-
ing a resistor between Rt and Gnd. By floating the pin, the switching frequency will be
200KHz and by grounding the pin, the switching frequency will be 400KHz.
Sync
The internal oscillator may be synchronized to an external clock via this pin.
VcH2
Supply voltage for the high side output drivers. These are connected to voltages that must
VcH1
be at least 4V higher than their bus voltages (assuming 5V threshold MOSFET). A mini-
mum of 1mF, high frequency capacitor must be connected from these pins to PGnd to
provide peak drive current capability.
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PIN SYMBOL
V
REF
Vp2
3
21
4
5,6
7
8
9
16
Rev. 1.9
09/27/02
3
IRU3046
PIN#
10,15
PIN SYMBOL
HDrv2, HDrv1
PIN DESCRIPTION
Output driver for the 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 the fast load transient from full load to no load.
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. A high frequency capacitor (0.1 to 1mF) must be connected
from Vcc, V
CL
, VcH1 and VcH2 pins to this pin for noise free operation.
Supply voltage for the low side output drivers.
Separate input supply for LDO controller.
Driver signal for the LDO’s external transistor.
LDO’s feedback pin, connected to a resistor divider to set the output voltage of LDO.
This pin provides soft-start for the switching regulator. An internal current source charges
an external capacitor that is connected from this pin to ground which ramps up the output
of the switching regulator, preventing it from overshooting as well as limiting the input
current. The converter can be shutdown by pulling this pin below 0.5V.
Sense the LDO input voltage for UVLO.
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.
Analog ground for internal reference and control circuitry. Connect to PGnd with a short
trace.
11,14
12
LDrv2, LDrv1
PGnd
13
17
18
19
20
V
CL
VccLDO
V
OUT3
Fb3
SS
22
23
24
V
SEN33
PGood
Gnd
BLOCK DIAGRAM
Vcc
4
10K
25uA
Bias
Generator
64uA Max
4.2V / 4.0V
16
VcH1
3V
1.25V
POR
15
HDrv1
V
SEN33 22
2.5V / 2.3V
3.5V / 3.3V
3.5V / 3.3V
4.2V / 4.0V
UVLO
SS
20
POR
Vsen33
VcH1
VcH2
VccLDO
13
V
CL
PWM Comp1
25K
1.25V
25K
Ramp1
Set1
Two Phase
Oscillator
Ramp2
Set2
10
HDrv2
Error Amp1
14
LDrv1
S
Q
R
Reset Dom
9
SS>2V
Fb1
21
Comp1
5
VcH2
Rt
7
Sync
8
1.25V
25K
Error Amp2
S
PWM Comp2
V
REF 1
Vp2
2
Q
R
25K
Reset Dom
0.5V
11
LDrv2
12
PGnd
POR
Fb1
Fb2
Fb3
PGood
23
PGood
17
VccLDO
Fb2
3
Fb2 Monitor Shut Down
Comp2
6
25K
1.25V
25K
40mA LDO Controller
SS
2V
24
Gnd
18
V
OUT3
Fb3
19
Figure 2 - Block diagram of the IRU3046.
4
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Rev. 1.9
09/27/02
IRU3046
THEORY OF OPERATION
Introduction
The IRU3046 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 and can be programmed by us-
ing an external resistor from 200KHz to 400KHz per
phase. Figure 11 shows switching frequency versus ex-
ternal resistor.
Independent Mode
In this mode the IRU3046 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 Block Diagram) mea-
sures the voltage drops across the current sense resis-
tors, 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 IRU3046 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 contribute to a smaller out-
put capacitor for the same ripple voltage requirement.
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.
Rev. 1.9
09/27/02
Soft-Start
The IRU3046 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, VcH2, VccLDO
and V
SEN
33 rise above their threshold and generates the
Power On Reset (POR) signal. Soft-start function oper-
ates by sourcing an internal current to charge an exter-
nal capacitor to about 3V. Initially, the soft-start function
clamps the E/A’s output of the PWM converter. As the
charging voltage of the external capacitor ramps up, the
PWM signals increase from zero to the point the feed-
back 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 IRU3046 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
IRU3046 protects the circuit for shorted output by sens-
ing the output voltages. The IRU3046 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.
Frequency Synchronization
The IRU3046 can be synchronized with an external clock
signal. The synchronizing pulses must have a minimum
pulse width of 100ns. If the sync function is not used,
the Sync pin can be either connected to ground or be
floating.
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