View IRU3046_183893.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

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 Configuration 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 controller 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 driving 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 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 VCL C5 3.3V C6 VOUT2 C7 R2 C8 C9 R3 R4 Comp2 HDrv2 Q1 R1 Vcc VccLDO VSEN33 VOUT3 Fb3 IRU3046 Rt Sync Comp1 VcH1 VcH2 HDrv1 Q2 C13 C12 L2
D1
D2
C11
C14
L3
R5 VOUT1 C16
LDrv1
Q3
C15 R6
U1
PGnd VREF 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
TA (C) 0 To 70
Rev. 1.9 09/27/02
DEVICE IRU3046CF
PACKAGE 24-Pin Plastic TSSOP (F) www.irf.com
FREQUENCY 200-400KHz
1
IRU3046
ABSOLUTE MAXIMUM RATINGS
Vcc Supply Voltage .................................................. VccLDO, VcH1, VcH2 and VCL Supply Voltage ........... Storage Temperature Range ...................................... Operating Junction Temperature Range ..................... 25V 30V (not rated for inductive load) -65C To 150C 0C To 125C
PACKAGE INFORMATION
24-PIN PLASTIC TSSOP (F)
TOP VIEW
VREF 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 VSEN33 21 Fb1 20 SS 19 Fb3 18 VOUT3 17 VccLDO 16 VcH1 15 HDrv1 14 LDrv1 13 VCL
JA = 84C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc=5V, VcH1=VcH2=VCL=VccLDO=12V and TA=0 to 70C. Typical values refer to TA=25C. 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 UVLO Threshold - VSEN33 UVLO Hysteresis - VSEN33 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 VFB LREG TEST CONDITION MIN 1.225 5Rev. 1.9 09/27/02
UVLOVCC Supply Ramping Up UVLOVCCLDO Supply Ramping Up UVLOVCH1 Supply Ramping Up UVLOVCH2 Supply Ramping Up UVLOFb Fb Ramping Down
UVLOVSEN33 Supply Ramping Up
Dyn ICC Dyn ICH1 Dyn ICH2 ICCQ ICH1Q ICH2Q ICLDO
Freq=200KHz, CL=1500pF Freq=200KHz, CL=1500pF Freq=200KHz, CL=1500pF SS=0V SS=0V SS=0V SS=0V www.irf.com
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 SSIB PGFB1L PGFB1H PGFB2L PGFB2H PGFB3L PGFB3H VPG IFB1 IFB2 gm1 gm2 VOS(ERR)2 Freq VRAMP Tr Tf TDB TON TOFF ILDO VFBLDO ILDO(BIAS) CL=1500pF CL=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 0.9VREF 1.1VREF 0.9VREF 1.1VREF 0.9VREF 1.1VREF 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 VP2 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 connected 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. 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 connecting 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 minimum of 1mF, high frequency capacitor must be connected from these pins to PGnd to provide peak drive current capability. www.irf.com PIN SYMBOL VREF 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, VCL, 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
VCL VccLDO VOUT3 Fb3 SS
22 23 24
VSEN33 PGood Gnd
BLOCK DIAGRAM
Vcc
4 10K 25uA Bias Generator 64uA Max
4.2V / 4.0V
16 VcH1 3V 1.25V POR 15 HDrv1
VSEN33 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 VCL
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
VREF 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 VOUT3
Fb3 19
Figure 2 - Block diagram of the IRU3046.
4
www.irf.com
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 linear regulator controller. The two synchronous controller operates with fixed frequency voltage mode and can be configured as two independent controller or 2-phase controller with current sharing. The timing of the IC is provided through an internal oscillator circuit. These are two out of phase oscillators and can be programmed by using an external resistor from 200KHz to 400KHz per phase. Figure 11 shows switching frequency versus external resistor. Independent Mode In this mode the IRU3046 provides two independent outputs with either common or different input voltages. The output voltage of the individual channel is set and controlled 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 variable duty-cycle, which drives the two N-channel external 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) 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 IRU3046 drives its two output stages 180o 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 output capacitor for the same ripple voltage requirement. In application with single input voltage, the 2-phase configuration 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 sequence initiates when the Vcc, VcH1, VcH2, VccLDO and VSEN33 rise above their threshold and generates the Power On Reset (POR) signal. Soft-start function operates by sourcing 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 voltage of the external capacitor ramps up, the PWM signals 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 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 sensing the output voltages. The IRU3046 shuts down the PWM signals and LDO controller, when the output voltages 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.
www.irf.com
5
IRU3046
APPLICATION INFORMATION
Design Example: The following example is a typical application for IRU3046 in current sharing mode. The schematic is Figure 13 on page 15. For Switcher: VIN1(MASTER) = 5V VIN2(SLAVE) = 12V VOUT1 = 1.5V IOUT = 16A DVOUT = 75mV fS = 200KHz PWM Section Output Voltage Programming Output voltage is programmed by reference voltage and external voltage divider. The Fb1 pin is the inverting input of the error amplifier, which is internally referenced to 1.25V. The divider is ratioed to provide 1.25V at the Fb1 pin when the output is at its desired value. The output voltage is defined by using the following equation: VOUT1 = VREF 3 For Linear Regulator: VIN3 = 3.3V VOUT2 = 2.5V IOUT2 = 2A Soft-Start Programming The soft-start timing can be programmed by selecting the soft start capacitance value. The start up time of the converter can be calculated by using:
tSTART = 75 3 Css (ms)
---(2)
Where: CSS is the soft-start capacitor (mF) For a start-up time of 7.5ms, the soft-start capacitor will be 0.1mF. Choose a ceramic capacitor at 0.1mF. Boost Supply To drive the high-side switch it is necessary to supply a gate voltage at least 4V greater than the bus voltage. This is achieved by using a charge pump configuration as shown in Figure 1. The capacitor is charged up to approximately twice the bus voltage. A capacitor in the range of 0.1mF to 1mF is generally adequate for most applications. Sense Resistor Selection These resistors will determine the current sharing between two channels. The relationship between the Master and Slave output currents is expressed by: RSEN1 3 IMASTER = RSEN2 3 ISLAVE ---(3)
(
R6 1+ R5
)
---(1)
When an external resistor divider is connected to the output as shown in Figure 3.
VOUT1 IRU3046
Fb1 R5 R6
For an equal current sharing, RSEN1=RSEN1 Choose RSEN1=RSEN2=5mV Input Capacitor selection The input filter capacitor should be based on how much ripple the supply can tolerate on the DC input line. The ripple current generated during the on time of control MOSFET should be provided by input capacitor. The RMS value of this ripple is expressed by: IRMS = IOUT D3(1-D) ---(4)
Figure 3 - Typical application of the IRU3046 for programming the output voltage. Equation (1) can be rewritten as: R6 = R5 3
( VOUT1 - 1) VREF
Where: D is the Duty Cycle, simply D=VOUT/VIN. IRMS is the RMS value of the input capacitor current. IOUT is the output current for each channel. For VIN1=5V, IOUT1=8A and D1=0.3 Results to: IRMS1=3.6A And for VIN2=12V, IOUT2=8A and D2=0.125 Results to: IRMS2=2.6A
This will result to: VOUT1 = 1.5V, VREF = 1.25V, R5 = 1K, R6 = 200V If the high value feedback resistors are used, the input bias current of the Fb pin could cause a slight increase in output voltage. The output voltage set point can be more accurate by using precision resistor.
6
www.irf.com
Rev. 1.9 09/27/02
IRU3046
For higher efficiency, a low ESR capacitor is recommended. For VIN1=5V, choose two Poscap from Sanyo 6TPB330M (6.3V, 330mF, 40mV, 3A) For VIN2=12V, choose two 16TPB47M (16V, 47mF, 70mV, 1.4A). 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 stability requirements. The ESR of the output capacitor is calculated by the following relationship: DVO ESR [ DIO ---(5) For the buck converter, the inductor value for desired operating ripple current can be determined using the following relation: Di VOUT 1 VIN - VOUT = L3Dt ; Dt = D3 ; D = VIN fS VOUT L = (VIN - VOUT)3 ---(6) VIN3Di3fS Where: VIN = Maximum Input Voltage VOUT = Output Voltage i = Inductor Ripple Current fS = Switching Frequency t = Turn On Time D = Duty Cycle For Di1=30% of I1, we get: L1=2.18mH For Di2=30% of I2, we get: L2=2.7mH The Coilcraft DO5022HC series provides a range of inductors in different values and low profile for large currents. For L1 choose: DO5022P-222HC (2.2mH,12A) For L2 choose: DO5022P-332HC (3.3mH,10A) Power MOSFET Selection The selections 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 MOSFET must have a maximum operating voltage (VDSS) exceeding the maximum input voltage (VIN). The gate drive requirement is almost the same for both MOSFETs. Caution should be taken with devices at very low VGS to prevent undesired turn-on of the complementary MOSFET, which results a shoot-through current. The total power dissipation for MOSFETs includes conduction and switching losses. For the Buck converter the average inductor current is equal to the DC load current. The conduction loss is defined as: PCOND (Upper Switch) = ILOAD 3 RDS(ON) 3 D 3 q PCOND (Lower Switch) = ILOAD 3 RDS(ON) 3 (1 - D) 3 q q = RDS(ON) Temperature Dependency The total conduction loss is defined as:
PCON(TOTAL)=PCON(Upper Switch)q + PCON(Lower Switch)q
2 2
Where: DVO = Output Voltage Ripple DIO = Output Current DVO=75mV and DIO=10A, result to ESR=7.5mV The Sanyo TPC series, Poscap capacitor is a good choice. The 6TPC150M 150mF, 6.3V has an ESR 40mV. Selecting six of these capacitors in parallel, results to an ESR of 7mV which achieves our low ESR goal. The capacitor value must be high enough to absorb the inductor's ripple current. The larger the value of capacitor, the lower will be the output ripple voltage. The resulting output ripple current is smaller then each channel ripple current due to the 1808 phase shift. These currents cancel each other. The cancellation is not the maximum because of the different duty cycle for each channel. Inductor Selection The inductor is selected based on output power, operating frequency and efficiency requirements. Low inductor value causes large ripple current, resulting in the smaller size, but poor efficiency and high output noise. Generally, the selection of inductor value can be reduced to desired maximum ripple current in the inductor (i); the optimum point is usually found between 20% and 50% ripple of the output current.
Rev. 1.9 09/27/02
www.irf.com
7
IRU3046
The RDS(ON) temperature dependency should be considered for the worst case operation. This is typically given in the MOSFET data sheet. Ensure that the conduction losses and switching losses do not exceed the package ratings or violate the overall thermal budget. Choose IRF7460 for control MOSFET and IRF7457 for synchronous MOSFET. These devices provide low onresistance in a compact SOIC 8-Pin package. The MOSFETs have the following data: IRF7460 IRF7457 VDSS = 20V VDSS = 20V ID = 10A @ 758C ID = 12A @ 708C RDS(ON) = 10mV @ RDS(ON) = 7.5mV @ VGS=10V VGS=10V q = 1.8 for 1508C q = 1.5 for 1508C (Junction Temperature) (Junction Temperature) The total conduction losses for the master channel is: PCON(MASTER) = 0.85W The total conduction losses for the slave channel is: PCON(SLAVE) = 0.77W The control MOSFET contributes to the majority of the switching losses in synchronous Buck converter. The synchronous MOSFET turns on under zero-voltage condition, therefore the turn on losses for synchronous MOSFET can be neglected. With a linear approximation, the total switching loss can be expressed as: VDS(OFF) tr + tf 3 3 ILOAD ---(7) 2 T Where: VDS(OFF) = Drain to Source Voltage at off time tr = Rise Time tf = Fall Time T = Switching Period ILOAD = Load Current PSW =
VDS 90%
0dB -40dB/decade 08
From IRF7460 data sheet we obtain: IRF7460
tr = 6.9ns tf = 4.3ns
These values are taken under a certain condition test. For more detail please refer to the IRF7460 and IRF7457 data sheets. By using equation (7), we can calculate the switching losses. PSW(MASTER) = 44.8mW PSW(SLAVE) = 107.5mW Feedback Compensation The control scheme for master and slave channels is based on voltage mode control, but the compensation of these two feedback loops is slightly different. The Master channel sets the output voltage and its feedback loop should take care of double pole introduced by the output filter as a regular voltage mode control loop. The goal is to provide a close loop transfer function with the highest 0dB crossing frequency and adequate phase margin. The slave feedback loop acts slightly different and its goal is using the current information for current sharing. The master feedback loop sees the output filter. The output LC filter introduces a double pole, -40dB/decade gain slope above its corner resonant frequency, and a total phase lag of 1808 (see Figure 5). The resonant frequency of the LC filter expressed as follows: FLC(MASTER) = 1 2p Lo3Co ---(8)
Figure 5 shows gain and phase of the LC filter. Since we already have 1808 phase shift just from the output filter, the system risks being unstable.
Gain Phase
10% VGS td(ON) tr td(OFF) tf
FLC Frequency
-1808
FLC
Frequency
Figure 5 - Gain and phase of LC filter.
Figure 4 - Switching time waveforms.
8
www.irf.com
Rev. 1.9 09/27/02
IRU3046
The master error amplifier is a differential-input transconductance amplifier. The output is available for DC gain control or AC phase compensation. The E/A can be compensated with or without the use of local feedback. When operated without local feedback the transconductance properties of the E/A become evident and can be used to cancel one of the output filter poles. This will be accomplished with a series RC circuit from Comp1 pin to ground as shown in Figure 6. The ESR zero of the LC filter expressed as follows: FESR = 1 2p3ESR3Co
VOUT R6 Fb1 Comp1 E/A1 R5 VREF
Gain(dB)
First select the desired zero-crossover frequency (Fo): FO1 > FESR and FO1 [ (1/5 ~ 1/10)3 fS Use the following equation to calculate R4: R4 = 1 VOSC FO13FESR R5 + R6 3 3 3 VIN(MASTER) FLC2 R5 gm ---(13)
---(9)
Where: VIN(MASTER) = Maximum Input Voltage VOSC = Oscillator Ramp Voltage FO1 = Crossover Frequency for the master E/A FESR = Zero Frequency of the Output Capacitor FLC(MASTER) = Resonant Frequency of Output Filter gm = Error Amplifier Transconductor R5 and R6 = Resistor Dividers for Output Voltage Programming For: VIN(MASTER) = 5V VOSC = 1.25V FO1 = 30KHz FESR = 25.26KHz FLC(MASTER) = 3.57KHz R5 = 1K R6 = 200V gm = 600mmho This results to: R4=29.7KV. Choose: R4=29.4KV To cancel one of the LC filter poles, place the zero before the LC filter resonant frequency pole: FZ 75%FLC(MASTER) FZ 0.75 3 1 2p LO 3 CO ---(14)
V e C9 R4
H(s) dB
FZ
Frequency
Figure 6 - Compensation network without local feedback and its asymptotic gain plot. The transfer function (Ve / VOUT) is given by: H(s) = gm3
(
R5 R6 + R5
sR4C9 ) 3 1 +sC9
---(10)
The (s) indicates that the transfer function varies as a function of frequency. This configuration introduces a gain and zero, expressed by: |H(s)| = gm 3 R5 3 R4 R6 3 R5 ---(12) ---(11)
For: Lo = 2.2mH Co = 900mF Fz = 2.67KHz R4 = 24.9KV Using equations (12) and (14) to calculate C9, we get: C9 = 2003pF Choose: C9 = 2200pF One more capacitor is sometimes added in parallel with C9 and R4. This introduces one more pole which is mainly used to suppress the switching noise. The additional pole is given by: 1 FP = C9 3 CPOLE 2p 3 R4 3 C9 + CPOLE
1 FZ = 2p 3 R4 3 C9
The gain is determined by the voltage divider and E/A's transconductance gain.
Rev. 1.9 09/27/02
www.irf.com
9
IRU3046
The pole sets to one half of switching frequency which results in the capacitor CPOLE: 1 1 CPOLE = p 3 R4 3 fS 1 p 3 R4 3 fS C9 fS For FP << 2 For a general solution for unconditionally stability for any type of output capacitors, in a wide range of ESR values we should implement local feedback with a compensation network. The typically used compensation network for voltage-mode controller is shown in Figure 7.
ZIN C10 R8 R6 Fb1 R5 VREF VOUT C12 R7 C11 Zf
As known, transconductance amplifier has high impedance (current source) output, therefore, consider should be taken when loading the E/A output. It may exceed its source/sink output current capability, so that the amplifier will not be able to swing its output voltage over the necessary range. The compensation network has three poles and two zeros and they are expressed as follows: FP1 = 0 FP2 = FP3 = 1 2p3R83C10 1 2p3R73 FZ1 = FZ2 =
(C123C11) C12+C11
1 2p3R73C12
1 2p3R73C11 1 1 2p3C103(R6 + R8) 2p3C103R6
E/A1 Comp1
V e
Gain(dB)
Cross Over Frequency: VIN 1 FO1 = R73C103 3 VOSC 2p3Lo3Co Where: VIN = Maximum Input Voltage VOSC = Oscillator Ramp Voltage Lo = Output Inductor Co = Total Output Capacitors
---(16)
H(s) dB
FZ1
FZ2
FP2
FP3
Frequency
Figure 7 - Compensation network with local feedback and its asymptotic gain plot. In such configuration, the transfer function is given by: 1Ve = VOUT 1 +
gmZf gmZIN
The stability requirement will be satisfied by placing the poles and zeros of the compensation network according to following design rules. The consideration has been taken to satisfy condition (15) regarding transconductance error amplifier. 1) Select the crossover frequency: Fo < FESR and Fo [ (1/10 ~ 1/6)3 fS 2) Select R7, so that R7 >> 2
The error amplifier gain is independent of the transconductance under the following condition:
gmZf >> 1
and
gmZIN >>1
---(15)
By replacing ZIN and Zf according to figure 7, the transformer function can be expressed as: (1+sR7C11)3[1+sC10(R6+R8)] 3 H(s)= sR6(C12+C11) 1+sR7 C12C11 3(1+sR8C10) C12+C11 1
gm
3) Place first zero before LC's resonant frequency pole. FZ1 75% FLC C11 = 1 2p 3 FZ1 3 R7
[
(
)]
10
www.irf.com
Rev. 1.9 09/27/02
IRU3046
4) Place third pole at the half of the switching frequency. FP3 = C12 = fS 2 1 2p 3 R7 3 FP3 The transfer function of power stage is expressed by: IL2(s) VIN - VOUT G(s) = = ---(17) Ve(s) sL2 3 VOSC Where: VIN = Input Voltage VOUT = Output Voltage L2 = Output Inductor VOSC = Oscillator Peak Voltage As shown the transfer function is a function of inductor current. The transfer function for the compensation network is given by equation (18), when using a series RC circuit as shown in Figure 8: D(s) = Ve(s) = RS2 3 IL2(s) sC2R2 (gm3 RS1)3(1 +sC2 ) ---(18) RS2
C12 > 50pF If not, change R7 selection. 5) Place R7 in (16) and calculate C10: C10 [ 2p 3 Lo 3 FO 3 Co VOSC 3 R7 VIN
6) Place second pole at ESR zero. FP2 = FESR R8 = 1 2p 3 C10 3 FP2 1
Check if R8 >
gm
IL2 L2 Fb2 Comp2 Vp2 RS1 L1 IL1 E/A2 R2 C2 V e
If R8 is too small, increase R7 and start from step 2. 7) Place second zero around the resonant frequency. FZ2 = FLC R6 = 1 - R8 2p 3 C10 3 FZ2
RS2
8) Use equation (1) to calculate R5: R5 = VREF 3 R6 VOUT - VREF
These design rules will give a crossover frequency approximately one-tenth of the switching frequency. The higher the band width, the potentially faster the load transient speed. The gain margin will be large enough to provide high DC-regulation accuracy (typically -5dB to 12dB). The phase margin should be greater than 458 for overall stability. The slave error amplifier is a differential-input transconductance amplifier as well, the main goal for the slave feed back loop is to control the inductor current to match the masters inductor current as well provides highest bandwidth and adequate phase margin for overall stability.
Figure 8 - The PI compensation network for slave channel. The loop gain function is: H(s)=[G(s) 3 D(s) 3 RS2] H(s)=RS23 VIN-VOUT (gm3 RS1)3 (1+sR2C2) 3(sL23VOSC) RS2 sC2
Select a zero crossover frequency (FO2) one-tenth of the switching frequency: FO2 = fS 10
FO2 = 20KHz
Rev. 1.9 09/27/02
www.irf.com
11
IRU3046
H(Fo) = gm3RS13R23 VIN - VOUT =1 2p3Fo3L23VOSC ---(19) LDO Power MOSFET Selection The first step in selecting the power MOSFET for the linear regulator is to select the maximum RDS(ON) based on the input to the dropout voltage and the maximum load current. RDS(ON) = VIN3 - VOUT2 IOUT2
From (18), R2 can be express as: R2 = 1 2p 3 FO2 3 L2 3 VOSC 3 VIN(SLAVE) - VOUT gm 3 RS1 ---(20)
Set the zero of compensator to be half of FLC(SLAVE), the compensator capacitor, C2, can be calculated as: FLC(SLAVE) = Fz = C2 = 1 2p L23COUT
For: VIN3 = 3.3V VOUT2 = 2.5V IOUT2 = 2A Results to: RDS(ON)(MAX) = 0.4V Note that since the MOSFET RDS(ON) increases with temperature, this number must be divided by ~1.5 in order to find the RDS(ON)(MAX) at room temperature. The IRLR2703 has a maximum of 0.065V RDS(ON) at room temperature, which meets our requirements. Layout Consideration The layout is very important when designing high frequency switching converters. Layout will affect noise pickup and can cause a good design to perform with less than expected results. Start to place the power components, make all the connection in the top layer with wide, copper filled areas. The inductor, output capacitor and the MOSFET should be close to each other as possible. This helps to reduce the EMI radiated by the power traces due to the high switching currents through them. Place input capacitor directly to the drain of the high-side MOSFET, to reduce the ESR replace the single input capacitor with two parallel units. The feedback part of the system should be kept away from the inductor and other noise sources, and be placed close to the IC. In multilayer PCB use one layer as power ground plane and have a control circuit ground (analog ground), to which all signals are referenced. The goal is to localize the high current path to a separate loop that does not interfere with the more sensitive analog control function. These two grounds must be connected together on the PC board layout at a single point.
FLC(SLAVE) 2 1 2p 3 R2 3 Fz ---(21)
Using equations (20) and (21) we get the following values for R2 and C2. R2=16.45K; Choose: R2=16.5K C2=6606pF; Choose: C2=6800pF LDO Section Output Voltage Programming Output voltage for LDO is programmed by reference voltage and external voltage divider. The Fb3 pin is the inverting input of the error amplifier, which is internally referenced to 1.25V. The divider is ratioed to provide 1.25V at the Fb3 pin when the output is at its desired value. The output voltage is defined by using the following equation: R7 VOUT2 = VREF3 1+ R10 For: VOUT2 = 2.5V VREF = 1.25V R10 = 1KV
(
)
Results to R7=1KV
VOUT3 IRU3046
Fb3 R10 R7
Figure 9 - Programming the output voltage for LDO.
12
www.irf.com
Rev. 1.9 09/27/02
IRU3046
TYPICAL APPLICATION
D1 12V C2 33uF L2 1uH C11 0.1uF D2 L1 5V C1 33uF 1uH C3 1uF C5 1uF 3.3V C6 47uF 2.5V @ 2A Q1 IRLR2703 R1 Fb3 C7 47uF 1K R2 1K R3 C8 2200pF Comp1 22K LDrv2 R4 C9 25K 1500pF PGood C10 0.1uF Comp2 PGood SS R5 1K R9 1K Q5 IRF7457 Rt Sync C4 1uF C13 VC L Vcc VccLDO VSEN33 VOUT3 LDrv1 PGnd Q3 IRF7457 VcH1 VcH2 HDrv1 1uF C14 2x 47uF Q2 IRF7460 L3 4.7uH 1.8V @ 8A C16 2x 150uF R7 442V C17 2x 150uF Q4 IRF7457 L4 3.9uH 2.5V @ 8A C12 2x 150uF R8 1K
U1 IRU3046
Fb1 VREF
Vp2 HDrv2
Fb2 Gnd
Figure 10 - Typical application for IRU3046 configured as two independent controllers.
Switching Frequency vs. Rt
400 370 340 Fs (KHz) 310 280 250 220 190 0 100 200 300 Rt Figure 11 - Switching frequency per phase vs. Rt 400 500 600
Rev. 1.9 09/27/02
www.irf.com
13
IRU3046
TYPICAL APPLICATION
12V
L1 5V C1 33uF 1uH C3 1uF C5 1uF 3.3V C6 47uF 1.8V @ 2A Q1 IRLR2703 R1 Fb3 C7 47uF 442 R2 1K R3 C8 16.2K 3900pF R4 C9 10K 5600pF PGood C10 0.1uF Comp2 Fb2 PGood SS Vp2 Gnd R9 1K R5 VDDQ 1K Comp1 LDrv2 Rt Sync C4 1uF C13 1uF VCL Vcc VccLDO VSEN33 VOUT3 LDrv1 PGnd VcH1 VcH2 HDrv1 1/2 of D1 BAT54A 1/2 of Q2 IRF7313 1/2 of Q2 IRF7313 R7 1K R8 1K L2 5.6uH VDDQ 2.5V @ 4A C16 330uF C14 150uF
U1 IRU3046
Fb1 C17 2x 150uF 1/2 of Q3 IRF7313 1/2 of Q3 IRF7313 L3 4.7uH VTT 1.25V @ 4A C12 330uF
VREF HDrv2 1/2 of D1 BAT54A
Figure 12 - Typical application for IRU3046 configured for DDR memory application.
14
www.irf.com
Rev. 1.9 09/27/02
IRU3046
DEMO-BOARD APPLICATION
Dual Input: 5V and 12V to 1.5V @ 16A
5V 12V L2 1uH C2 33uF L1 1uH C1 33uF
D1 BAT54S C3
0.1uF C7 1uF C9 1uF
C4 47uF C32 47uF
C5 330uF C31 330uF C6 1uF
VCL C8 1uF 3.3V R6 10V C13 47uF Q3 IRLR2703 2.5V @ 2A C30 1uF R7 1K C18 47uF R10 1K Rt Sync R13 15K R16 29.4K R21 16.5K C24 2200pF C34 6.8nF Comp1 Vcc VccLDO VSEN33 VOUT3
VH c1
VH c2 HDrv1
D2 BAT54A
Q1 IRF7460
L3 2.2uH R3 C14 470pF R5 4.7V 5m V
C10,C11,C12 3x 150uF C15 1uF
1.5V @ 16A
LDrv1 PGnd VREF Vp2 Fb1 Fb2
Q2 IRF7457
Fb3
U1 IRU3046
R8 200
Comp2
HDrv2 D4 BAT54A
Q4 IRF7460
C23 1uF L4 3.3uH C26 470pF R19 4.7V R17 5mV
R12 1K
C19,C20,C21 3x 150uF
PGood
PGood SS C29 0.1uF LDrv2 Gnd
Q5 IRF7457
Figure 13 - Demo-board application of IRU3046.
Rev. 1.9 09/27/02
www.irf.com
15
IRU3046
DEMO-BOARD APPLICATION
Application Parts List Ref Desig Q1,Q4 Q2,Q5 Q3 U1 D1 D2,D4 L1,L2 L3 L4 C1,C2 C4,C32 C5,C31 C10,11,12, 19,20,21 C3,C29 C9 C24 C34 C14,C26 C6,7,8, 15,23,30 C13,C18 R2,4,15,18 R16 R21 R5,R19 R8 R7,10,12 R3,R17 R13 R6 Description MOSFET MOSFET MOSFET Controller Diode Diode Inductor Inductor Inductor Cap, Tantalum Cap, Poscap Cap, Poscap Cap, Poscap Cap, Cap, Cap, Cap, Cap, Cap, Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Value Qty Part# 20V, 10mV, 12A 2 IRF7460 20V, 7mV, 15A 2 IRF7457 30V, 0.045V, 23A 1 IRLR2703 Synchronous PWM 1 IRU3046 Fast Switching 1 BAT54S Fast Switching 2 BAT54A or 1N4148 1mH, 6.8A 2 D03316P-102 2.2mH, 12A 1 D05022P-222HC 3.3mH, 10A 1 D05022P-332HC 33mF, 16V 2 ECS-T1CD336R 47mF, 16V 2 16TPB47M 330mF, 6.3V 2 6TPB330M 150mF, 6.3V, 40mV 6 6TPC150M 0.1mF, Y5V, 25V 1mF, X7R, 25V 2200pF, X7R, 50V 6800pF, X7R, 50V 470pF, X7R, 50V 1mF, Y5V, 16V 47mF, 10V 2.15V 29.4K 16.5K 4.7V 200, 1% 1K, 1% 5mV, 1W, 1% 15K 10V 2 1 1 1 2 6 2 4 1 1 2 1 3 2 1 1 ECJ-2VF1E104Z ECJ-3YB1E105K ECJ-2VB1H222K ECJ-2VB1H682K ECJ-2VC1H471J ECJ-2VF1C105Z ECS-T1AD476R Manuf IR IR IR IR IR IR Any Coilcraft Coilcraft Coilcraft Panasonic Sanyo Sanyo Sanyo Web site (www.) irf.com
coilcraft.com
maco.panasonic.co.jp sanyo.com/industrial
Panasonic maco.panasonic.co.jp Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic
Cap, Tantalum Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor
ERJ-M1WSF5MOU Panasonic
16
www.irf.com
Rev. 1.9 09/27/02
IRU3046
WAVEFORMS
Figure 14 - Gate signals vs. inductor currents. Ch1: Gate signal for control FET(master) (10V/div). Ch2: Gate signal for control FET(slave) (20V/div). Ch3: Inductor current for master channel (5A/div). Ch4: Inductor current for slave channel (5A/div). VMASTER=5V, VSLAVE=12V, IOUT=10A
Figure 15 - Inductors current matching. Ch1: Gate signal for sync FET(master) (10V/div). Ch2: Gate signal for sync FET(slave) (10V/div). Ch3: Inductor current for master channel (5A/div). Ch4: Inductor current for slave channel (5A/div). VMASTER=5V, VSLAVE=12V, IOUT=10A
Figure 16 - Gate signals. Ch1: Gate signal for control FET(master) (10V/div). Ch2: Gate signal for sync FET(master) (10V/div). Ch3: Gate signal for control FET(slave) (20V/div). Ch4: Gate signal for sync FET(slave) (10V/div).
Rev. 1.9 09/27/02
www.irf.com
17
IRU3046
WAVEFORMS
VIN=5V
Vss
10A
VOUT
0A
Figure 17 - Start-up @ IOUT = 10A.
Figure 18 - Transient response @ IOUT = 0 to 10A.
2A
0A
Figure 19 - Transient response for LDO @ IOUT = 0 to 2A.
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice. 02/01
18
www.irf.com
Rev. 1.9 09/27/02
IRU3046
(F) TSSOP Package 24-Pin
A L Q
R1 1.0 DIA B C R
E M O PIN NUMBER 1 F D DETAIL A P
N
G
DETAIL A
J
H
K
SYMBOL DESIG A B C D E F G H J K L M N O P Q R R1
MIN 4.30 0.19
7.70 --0.85 0.05
08 0.50 0.09 0.09
24-PIN NOM 0.65 BSC 4.40 6.40 BSC --1.00 1.00 7.80 --0.90 --128 REF 128 REF --1.00 REF 0.60 0.20 -----
MAX 4.50 0.30
7.90 1.10 0.95 0.15
88 0.75 -----
NOTE: ALL MEASUREMENTS ARE IN MILLIMETERS.
Rev. 1.9 09/27/02
www.irf.com
19
IRU3046
PACKAGE SHIPMENT METHOD
PKG DESIG F PACKAGE DESCRIPTION TSSOP Plastic PIN COUNT 24 PARTS PER TUBE 74 PARTS PER REEL 2500 T&R Orientation Fig A
1
1
1
Feed Direction Figure A
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice. 02/01
20
www.irf.com
Rev. 1.9 09/27/02

▲Up To Search▲

Price & Availability of IRU3046

	To Download IRU3046 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .