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PDF IRU3146 Data sheet ( Hoja de datos )
| Número de pieza | IRU3146 | |
| Descripción | DUAL SYNCHRONOUS PWM CONTROLLER | |
| Fabricantes | International Rectifier | |
| Logotipo |  |
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Data Sheet No.PD 94702
IRU3146
DUAL SYNCHRONOUS PWM CONTROLLER WITH
CURRENT SHARING CIRCUITRY AND AUTO-RESTART
FEATURES
Dual Synchronous Controller with 180 out-of-phase
Configurable to 2-Independent Outputs or 2-Phase
Single Output
Current Sharing Using Inductor's DCR
Current Limit using MOSFET's RDS(ON)
Hiccup/Latched Current Limit
www.DataSheet4U.comLatched Over-Voltage Protection
Vcc from 4.5V to 16V Input
Programmable Switching Frequency up to 500KHz
Two Independent Soft-Starts/ Shutdowns
0.8V Precision Reference Voltage Available
Power Good Output
External Frequency Synchronization
APPLICATIONS
Embedded Computer Systems
Telecom Systems
Point of Load Power Architectures
DESCRIPTION
The IRU3146 IC combines a Dual synchronous Buck
controller, providing a cost-effective, high performance
and flexible solution. The IRU3146 can configured as 2-
independent or as 2-phase controller. The 2-phase con-
figuration is ideal for high current applications. The
IRU3146 features 180 out of phase operation which re-
duces the required input/output capacitance and results
to few number of capacitor quantity. Other key features
offered by this device include two independent program-
mable soft starts, programmable switching frequency up
to 500KHz per phase, under voltage lockout function.
The current limit is provided by sensing the lower
MOSFET's on-resistance for optimum cost and perfor-
mance.
2-Phase Power Supply
Graphic Card
DDR Memory Applications
C12
12V
D1
C11
PGood
C3 C4
C5
R2
C8 R3
C9 R4
C10
VCL VcH1 VOUT3 VcH2
Vcc HDrv1
OCSet1
Hiccup
LDrv1
Sync
VREF
PGnd1
VP2
Rt U1
IRU3146 VSEN1
Comp1
VSEN2
Fb1
Fb2
C13
R1
Comp2
PGood
SS1 / SD
SS2 / SD
HDrv2
OCSet2
LDrv2
PGnd2
Gnd
R6
C14
Q2
Q3
D2
BAT54A
L3
R5
C15
C17
Q4
Q5
R9
C18
L4
1.8V @ 30A
R10
C16
R11
R7
R8
Figure 1 - Typical application of IRU3146 in 2-phase configuration with inductor current sensing
PACKAGE ORDER INFORMATION
DEVICE
IRU3146CF
PACKAGE
28-Pin TSSOP (F)
Rev. 1.1
6/25/04
www.irf.com
1
1 page  
IRU3146
PIN DESCRIPTIONS
PIN#
26
27
28
PIN SYMBOL
VP2
VREF
Gnd
PIN DESCRIPTION
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
VREF pin when Fb2 is connected to the resistor divider to set the output voltage.
Reference Voltage. The drive capability of this pin is about 2uA.
Analog ground for internal reference and control circuitry. Connect to PGnd plane with a
short trace.
1) These pins should not go negative (-0.5V), this may cause instability for the gate drive circuits. To prevent this,
a low forward voltage drop diode is required between these pins and ground as shown in Figure 1.
BLOCKwww.DataSheet4U.com DIAGRAM
Vcc 2
SS2 / SD 8
SS1 / SD 20
25uA 25uA
64uA
Max
64uA
POR
0.8V
Fb1 22
Comp1 21
Rt 4
Sync 24
VREF 27
VP2 26
Fb2 6
Comp2 7
VSEN1 23
VSEN2 5
Gnd 28
0.8V
Error Amp1
Error Amp2
Mode
Bias
Generator
3V
0.8V
VP2
0.8V
Mode
Control
VcH1
VcH2
4.2V / 4.0V
3.5V / 3.3V
3.5V / 3.3V
PWM Comp1
UVLO POR
Thermal
Shutdown
0.3V
SS1
R SS1
Q 3uA
Ramp1
Ramp2
Two Phase
Oscillator
Set1 S
Reset Dom
Set2
Reset Dom
S
PWM Comp2
Q
SS1
SS2
Hiccup
Control
R Mode
0.3V
SS2 SS2
PGood / OVP
OVP
HDrv OFF / LDrv ON
3uA
Regulator
POR
Mode
20uA
20uA
18 VcH1
17 HDrv1
14 VCL
15 LDrv1
16 PGnd1
19 OCSet1
10 VcH2
11 HDrv2
25 Hiccup
13 LDrv2
12 PGnd2
9 OCSet2
1 PGood
3 VOUT3
Figure 3 - Block diagram of IRU3146.
Rev. 1.1
6/25/04
www.irf.com
5
5 Page 
IRU3146
Input Capacitor Selection
The 1800 out of phase will reduce the RMS value of the
ripple current seen by input capacitors. This reduces
numbers of input capacitors. The input capacitors must
be selected that can handle both the maximum ripple
RMS at highest ambient temperature as well as the
maximum input voltage. The RMS value of current ripple
for duty cycles under 50% is expressed by:
IRMS= (I12D1(1-D1)+I22D2(1-D2)-2I1I2D1D2) --- (6)
www.DataSheet4U.cWomhere:
IRMS is the RMS value of the input capacitor current
D1 and D2 are the duty cycle for each output
I1 and I2 are the current for each output
For this application the IRMS =4.8A
For higher efficiency, low ESR capacitors is recom-
mended.
Choose two Poscap from Sanyo 16TPB47M (16V, 47µF,
70mΩ ) with a maximum allowable ripple current of 1.4A
for inputs of each channel.
Inductor Selection
The inductor is selected based on operating frequency,
transient performance and allowable output voltage ripple.
Low inductor value results to faster response to step
load (high ∆i/∆t) and smaller size but will cause larger
output ripple due to increase of inductor ripple current.
As a rule of thumb, select an inductor that produces a
ripple current of 10-40% of full load DC.
For the buck converter, the inductor value for desired
operating ripple current can be determined using the fol-
lowing relation:
VIN - VOUT = L×∆∆ti
;
∆t
=
D×
1
fS
L = (VIN - VOUT)×VIN×VO∆UiT×fS
Where:
VIN = Maximum Input Voltage
VOUT = Output Voltage
∆i = Inductor Ripple Current
fS = Switching Frequency
∆t = Turn On Time
D = Duty Cycle
;
D
=
VOUT
VIN
---(7)
For ∆i(2.5V) = 38%(IO(2.5V) ), then the output inductor will
be:
L4 = 1.71µH
For ∆i(1.8V) = 30%(IO(1.8V) ), then the output inductor will
be:
L3 = 1.7µH
Panasonic provides a range of inductors in different val-
ues and low profile for large currents.
Choose ETQP6F1R8BFA (1.71µH, 14A, 3.3mΩ) both
for L3 and L4.
For 2-phase application, equation (7) can be used for
calculating the inductors value. In such case the induc-
tor ripple current is usually chosen to be between 10-
40% of maximum phase current.
Output Capacitor Selection
The criteria to select the output capacitor is normally
based on the value of the Effective Series Resistance
(ESR). In general, the output capacitor must have low
enough ESR to meet output ripple and load transient
requirements, yet have high enough ESR to satisfy sta-
bility requirements. The ESR of the output capacitor is
calculated by the following relationship:
(ESL, Equivalent Series Inductance is neglected)
ESR
≤
∆VO
∆IO
---(8)
Where:
∆VO = Output Voltage Ripple
∆i = Inductor Ripple Current
∆VO = 3% of VO will result to ESR(2.5V) =19.7mΩ and
ESR(1.8V) =16mΩ
The Sanyo TPC series, Poscap capacitor is a good choice.
The 6TPC330M, 330µF, 6.3V has an ESR 40mΩ. Se-
lecting two of these capacitors in parallel for 2.5V out-
put, results to an ESR of ≅ 20mΩ which achieves our
low ESR goal. And selecting four of these capacitors in
parallel for 1.8V output, results to an ESR of ≅ 10mΩ
which achieves our low ESR goal.
The capacitors value must be high enough to absorb the
inductor's ripple current.
Power MOSFET Selection
The IRU3146 uses four N-Channel MOSFETs. The se-
lections criteria to meet power transfer requirements is
based on maximum drain-source voltage (VDSS), gate-
source drive voltage (VGS), maximum output current, On-
resistance RDS(ON) and thermal management.
The both control and synchronous MOSFETs must have
a maximum operating voltage (VDSS) that exceeds the
maximum input voltage (VIN).
Rev. 1.1
6/25/04
www.irf.com
11
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| PDF Descargar | [ Datasheet IRU3146.PDF ] | |
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