Technology Licensed from International Rectifier APU3146 DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND AUTO-RESTART DESCRIPTION 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 Latched 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 The APU3146 IC combines a Dual synchronous Buck controller, providing a cost-effective, high performance and flexible solution. The APU3146 can configured as 2independent or as 2-phase controller. The 2-phase configuration is ideal for high current applications. The APU3146 features 180 out of phase operation which reduces the required input/output capacitance and results to few number of capacitor quantity. Other key features offered by this device include two independent programmable 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 performance. 2-Phase Power Supply Graphic Card DDR Memory Applications Embedded Computer Systems Telecom Systems Point of Load Power Architectures D1 C12 12V C11 C3 C4 VCL VcH1 VOUT3 VcH2 HDrv1 Vcc C5 OCSet1 Hiccup VREF Rt C8 R3 LDrv1 C14 Q2 L3 Q3 R5 1.8V @ 30A C15 D2 BAT54A U1 APU3146 VSEN1 Comp1 C9 R1 PGnd1 VP2 Sync R2 C13 R10 C16 R11 R7 VSEN2 Fb1 Fb2 R8 R9 C17 R4 Comp2 HDrv2 C18 R6 Q4 L4 OCSet2 PGood PGood SS1 / SD C10 SS2 / SD LDrv2 Q5 PGnd2 Gnd Figure 1 - Typical application of APU3146 in 2-phase configuration with inductor current sensing PACKAGE ORDER INFORMATION DEVICE APU3146O(/M) Data and specifications subject to change without notice. PACKAGE 28-Pin TSSOP(/SOIC WB) 200407061-1/28 APU3146 ABSOLUTE MAXIMUM RATINGS Vcc, VCL Supply Voltage .............................................. -0.5V To 16V VcH1 and VcH2 Supply Voltage ................................ -0.5V To 25V PGOOD................. ................................................... -0.5V To 16V Storage Temperature Range ...................................... -40C To 125C Operating Junction Temperature Range ..................... -40C To 125C Caution: Stresses above those listed in Absolute Maximum Ratings" may cause permanent damage to the device. PACKAGE INFORMATION 28-PIN TSSOP (O) PGood 1 VCC 2 VOUT3 3 Rt 4 VSEN2 5 Fb2 6 Comp2 7 SS2 / SD 8 OCSet2 9 VcH2 10 28-PIN SOIC WIDE BODY(M) PGood 1 28 Gnd 27 VREF 28 Gnd 27 VREF VCC 2 26 VP2 26 VP2 VOUT3 3 Rt 4 25 Hiccup 24 Sync 25 Hiccup 24 Sync VSEN2 5 Fb2 6 23 VSEN1 22 Fb1 23 VSEN1 22 Fb1 Comp2 7 21 Comp1 SS2 / SD 8 20 SS1 / SD 21 Comp1 20 SS1 / SD OCSet2 9 19 OCSet1 19 OCSet1 VcH2 10 HDrv2 11 18 VcH1 HDrv2 11 18 VcH1 PGnd2 12 17 HDrv1 PGnd2 12 17 HDrv1 LDrv2 13 16 PGnd1 LDrv2 13 16 PGnd1 VCL 14 15 LDrv1 VCL 14 15 LDrv1 RthJA=80oC/W RthJA = 84C/W ELECTRICAL SPECIFICATIONS Unless otherwise specified, these specifications apply over Vcc=12V, VcH1=VcH2=VCL=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 Reference Voltage Voltage Line Regulation UVLO Section UVLO Threshold - Vcc UVLO Hysteresis - Vcc UVLO Threshold - VcH1 UVLO Hysteresis - VcH1 UVLO Threshold - VcH2 UVLO Hysteresis - VcH2 Supply Current Section Vcc Dynamic Supply Current VcH1 & VcH2 Dynamic Current VCL Dynamic Supply Current Vcc Static Supply Current VcH1/VcH2 Static Current VCL Static Supply Current SYM VREF LREG TEST CONDITION TYP MAX UNITS 0.789 0.805 0.02 0.821 0.04 V %/V 3.9 4.2 0.25 3.5 0.1 3.5 0.1 4.5 V V V V V V 10 15 15 10 6 6 15 25 25 15 10 10 5<Vcc<12 UVLOVCC Supply Ramping Up Ramp Up and Ramp Down UVLOVCH1 Supply Ramping Up Ramp Up and Ramp Down UVLOVCH2 Supply Ramping Up Ramp Up and Ramp Down Dyn ICC Dyn ICH Dyn ICL ICCQ ICHQ ICLQ MIN Freq=300KHz, CL=1500pF Freq=300KHz, CL=1500pF Freq=300KHz, CL=1500pF SS=0V SS=0V SS=0V 3.2 3.2 3.8 3.8 mA mA mA mA mA mA 2/28 APU3146 PARAMETER Soft-Start Section Charge Current Power Good Section VSENS1 Lower Trip Point VSENS2 Lower Trip Point PGood Output Low Voltage Error Amp Section Fb Voltage Input Bias Current Transconductance 1 Transconductance 2 Error Amp Source/Sink Current Input Offset Voltage for PWM1/2 VP2 Voltage Range Oscillator Section Frequency Ramp Amplitude Synch Frequency Range Synch Pulse Duration Synch High Level Threshold Synch Low Level Threshold VOUT3 Internal Regulator Output Voltage Output Current Protection Section OVP Trip Threshold OVP Fault Prop Delay Current Limit Threshold Current Source Hiccup Duty Cycle Hiccup High Level Threshold Hiccup Low Level Threshold Output Drivers Section Rise Time Fall Time Dead Band Time Max Duty Cycle Min Duty Cycle Min Pulse Width Thermal Shutdown Trip Point Thermal Shutdown Hysteresis SYM SSIB PGFB1L PGFB2H IFB1 gm1 gm2 VOS(ERR)2 VP2 TEST CONDITION SS=0V VSENS1 Ramping Down VSENS2 Ramping Down ISINK=2mA MIN TYP MAX UNITS 20 25 32 A 0.8VREF 0.9VREF 0.95VREF 0.8VREF 0.9VREF 0.95VREF 0.1 0.5 V V V -0.1 A mho mho A mV V SS=3V Fb to VREF Note1 1400 1400 60 -5 0.8 100 0 -0.5 2300 2300 140 +5 1.5 KHz Freq VRAMP Rt(SET) to 30K Note1 20% above free running freq Note1 Note1 255 345 1.25 800 200 2 300 0.8 5.9 50 OVP Output forced to 1.125VREF,Note1 OCSet 6.2 6.7 V KHz ns V V V mA 1.1VREF 1.15VREF 1.2VREF 5 16 20 24 V s A 5 % V V Hiccup pin pulled high, Note1 Note1 2 0.8 Tr Tf TDB DMAX DMIN Puls(min) CL=1500pF, Figure 2 CL=1500pF, Figure 2 Figure 2 Fb=0.6V, FSW=300KHz Fb=1V FSW=300KHz, Note1 Note 1 18 25 50 85 0 150 140 20 50 50 100 ns ns ns % % ns C C Note 1: Guaranteed by design but not tested for production. 3/28 APU3146 DEADBAND TIME Tf Tr 90% High Side Driver HD 2V 10% Tr Tf 90% Low Side Driver LD 2V 10% Deadband H_to_L Deadband L_to_H Figure 2 - Deadband time definition. TDB(TYP)=(Deadband H_toL+Deadband L_to -H)/2 PIN DESCRIPTIONS PIN# 1 2 3 4 5,23 6,22 7,21 8 20 9,19 10,18 11,17 12,16 13,15 14 24 25 PIN SYMBOL PGood Vcc VOUT3 Rt VSEN2, VSEN1 Fb2,Fb1 PIN DESCRIPTION Power Good pin. Low when any of the outputs fall 10% below the set voltages. Supply voltage for the internal blocks of the IC. Output of the internal LDO. Switching frequency setting resistor. (see Figure 10 for selecting resistor values). Sense pins for OVP and PGood. For 2-Phase operation tie these pins together. 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 2-channel mode, these pins work as feedback inputs for each channel. Comp2, Comp1 Compensation pins for the error amplifiers. These pins provide soft-start for the switching regulator. An internal current source charges external capacitors that are connected from these pins to ground which ramp up the SS2 / SD output of the switching regulators, preventing them from overshooting as well as limiting SS1 / SD the input current. The converter can be shutdown by pulling these pins below 0.3V. OCSet2,OCSet1 Current limit resistor (RLIM) connection pins for output 1 and 2. The other ends of RLIMs are connected to the corresponding switching nodes. VcH2, VcH1 Supply voltage for the high side output drivers. These are connected to voltages that must be typically 6V higher than their bus voltages. A 1F high frequency capacitor must be connected from these pins to GND to provide peak drive current capability. HDrv2, HDrv1 Output drivers for the high side power MOSFETs. 1) PGnd2, PGnd1 These pins serve as the separate grounds for MOSFET drivers and should be connected to the system's ground plane. LDrv2, LDrv1 Output drivers for the synchronous power MOSFETs. VCL Supply voltage for the low side output drivers. This pin should be high for normal operation The internal oscillator may be synchronized to an external clock via this pin. Sync When pulled High, it puts the device current limit into a hiccup mode. When pulled Low, Hiccup the output latches off, after an overcurrent event. 4/28 APU3146 PIN DESCRIPTIONS PIN# 26 PIN SYMBOL VP2 27 28 VREF Gnd PIN DESCRIPTION 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. 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. BLOCK DIAGRAM Vcc 2 25uA 25uA SS2 / SD 8 SS1 / SD 20 Mode 64uA Max 3V Bias Generator 64uA 0.8V 4.2V / 4.0V VcH1 VcH2 3.5V / 3.3V UVLO POR Mode POR 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 0.3V PWM Comp1 Thermal Shutdown SS1 Error Amp1 R 0.8V Comp1 21 Rt 4 Sync 24 VREF 27 SS1 3uA Q 22 Set1 Ramp1 Two Phase Oscillator S 20uA Reset Dom Set2 Ramp2 Reset Dom S PWM Comp2 0.8V Q R Error Amp2 VP2 Mode Control 3.5V / 3.3V POR Fb1 VP2 0.8V SS1 SS2 Hiccup Control Mode 26 0.3V Fb2 6 Comp2 7 VSEN1 23 VSEN2 5 Gnd 28 SS2 PGood / OVP OVP HDrv OFF / LDrv ON Regulator SS2 3uA 20uA Figure 3 - Block diagram of APU3146. 5/28 APU3146 FUNCTIONAL DESCRIPTION Introduction The APU3146 is versatile device for high performance Buck converters. It is included of two synchronous Buck controllers which can be operated both in two independent mode or in 2-phase mode. The timing of the IC is provided through an internal oscillator circuit. These are two out-of-phase oscillators that can be programmed up to 400KHz per phase. information for current sharing. The voltage drops across the current sense resistors (or DCR of inductors) are measured and their difference is amplified by the slave error amplifier and compared with the ramp signal to generate the PWM pulses to match the output current. In this mode the SS2 pin should be floating. APU3146 Supply Voltage Vcc is the supply voltage for internal controller. The operating range is from 4.5V to 16V. It also is fed to the internal LDO. When Vcc is below under-voltage threshold, all MOSFET drivers will be turned off. Internal Regulator The regulator powers directly from VCC and generates a regulated voltage (Typ. 6.2V@50mA). The output is protected for short circuit. This voltage can be used for charge pump circuitry as describe in Figure12. PWM Comp1 Comp Master E/A PWM Comp2 0.8V L1 Fb1 R1 RL1 VOUT C1 VP2 FB2 L2 RL2 Slave E/A R2 C2 Input Supplies UnderVoltage LockOut Figure 4 - Loss-less inductive current sensing The APU3146 UVLO block monitors three input voltages and current sharing. (VCC, VCH1 and VCH2) to ensure reliable start up. The MOSFET driver output turn off when any of the supply voltages drops below set thresholds. Normal operation In the diagram, L1 and L2 are the output inductors. RL1 resumes once the supply voltages rise above the set and RL2 are inherent inductor resistances. The resistor R1 and capacitor C1 are used to sense the average invalues. ductor current. The voltage across the capacitors C1 and C2 represent the average current flowing into resisIndependent Mode In this mode the APU3146 provides control to two inde- tance RL1 and RL2. The time constant of the RC network pendent output power supplies with either common or should be equal or at most three times larger than the different input voltages. The output voltage of each indi- time constant L1/R . L1 vidual channel is set and controlled by the output of the R1xC1=(1~3)x ---(1) L1 R error amplifier, which is the amplified error signal from the sensed output voltage and the reference voltage. The error amplifier output voltage is compared to the ramp signal thus generating fixed frequency pulses of variable duty-cycle, which are applied to the FET drivers, Figure18 shows a typical schematic for such application. L1 2-Phase Mode This feature allows to connect both outputs together to increase current handling capability of the converter to support a common load. The current sharing can be done either using external resistors or sensing the DCR of inductors (see Figure 4). 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 Figure 5 - 30A Current Sharing using Inductor sensing (5A/Div) 6/28 APU3146 Dual Soft-Start The APU3146 has programmable soft-start to control the output voltage rise and limit the inrush current during start-up. It provides a separate Soft-Start function for each outputs. This will enable to sequence the outputs by controlling the rise time of each output through selection of different value soft-start capacitors. The soft-start pins will be connected together for applications where, both outputs are required to ramp-up at the same time. To ensure correct start-up, the soft-start sequence initiates when the VCC, VCH1 and VCH2 rise above their threshold (4.2V and 3.5V respectively) and generate 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. During power up, the converter output starts at zero and thus the voltage at Fb is about 0V. A current (64A) injects into the Fb pin and generates a voltage about 1.6V (64Ax25K) across the negative input of E/A and (see Figure6). The magnitude of this current is inversely proportional to the voltage at soft-start pin. The 25A current source starts to charge up the external capacitor. In the mean time, the soft-start voltage ramps up, the current flowing into Fb pin starts to decrease linearly and so does the voltage at negative input of E/A. When the soft-start capacitor is around 1V, the current flowing into the Fb pin is approximately 32A. The voltage at the positive input of the E/A is approximately: 32Ax25K = 0.8V The E/A will start to operate and the output voltage starts to increase. As the soft-start capacitor voltage continues to go up, the current flowing into the Fb pin will keep decreasing. Because the voltage at pin of E/A is regulated to reference voltage 0.8V, the voltage at the Fb is: 25uA 25uA SS2 / SD 8 SS1 / SD 20 64uA POR Error Amp1 0.8V Fb1 22 Comp1 21 Error Amp2 VP2 26 Fb2 6 Comp2 7 Figure 6 -Soft-start circuit for APU3146 Output of POR 3V 2V Soft-Start Voltage Current flowing into Fb pin 1V 0V 64uA 0uA Voltage at negative input 1.6V of Error Amp 0.8V 0.8V VFB = 0.8-(25KxInjected Current) The feedback voltage increases linearly as the injecting current goes down. The injecting current drops to zero when soft-start voltage is around 2V and the output voltage goes into steady state. Figure 7 shows the theoretical operational waveforms during soft-start. 64uA Max Voltage at Fb pin 0V Figure 7 - Theoretical operational waveforms during soft-start. The output start-up time is the time period when softstart capacitor voltage increases from 1V to 2V. The start-up time will be dependent on the size of the external soft-start capacitor. The start-up time can be estimated by: 25AxTSTART/CSS = 2V-1V 7/28 APU3146 For a given start up time, the soft-start capacitor can be calculated by: CSS 25AxTSTART/1V The soft-start is part of Over Current Protection scheme, during the overload or short circuit condition the external soft start capacitors will be charged and discharged in certain slope rate to achieve the hiccup mode function. The internal current source develops a voltage across RSET. When the low side switch is turned on, the inductor current flows through the Q2 and results a voltage which is given by: VOCSET = IOCSETxRSET-RDS(ON)xiL ---(2) IOCSET 25uA APU3146 Hiccup Q1 L1 OCSet RSET SS1 / SD 20 3uA Figure 8 - 3uA current source for discharging soft start-capacitor during Hiccup mode Hiccup Control VOUT Q2 Figure 9 - Diagram of the over current sensing. The critical inductor current can be calculated by setting: Out-of-Phase Operation VOCSET = IOCSETxRSET - RDS(ON)xIL = 0 The APU3146 drives its two output stages 180 out-ofRSETxIOCSET phase. In 2-phase configuration, the two inductor ripple ISET = IL(CRITICAL)= ---(3) currents cancel each other and result in a reduction of RDS(ON) the output current ripple and yield a smaller output capacitor for the same ripple voltage requirement. In single input voltage applications, the input ripple current reduces. This result in much smaller input capacitor's RMS current and reduces the input capacitor quantity. The value of RSET should be checked in an actual circuit to ensure that the Over Current Protection circuit activates as expected. The APU3146 current limit is designed primarily as disaster preventing, "no Over-Current Protection blow up" circuit, and is not useful as a precision The APU3146 can provide two different schemes for Overcurrent regulator. Current Protection (OCP). When the pin Hiccup is pulled high, the OCP will operate in hiccup mode. In this mode, In two independent mode, the output of each channel during overload or short circuit, the outputs enter hiccup is protected independently which means if one output mode and stay in that mode until the overload or short is under overload or short circuit condition, the other circuit is removed. The converter will automatically reoutput will remain functional. The OCP set limit can be cover. programmed to different levels by using the external When the Hiccup pin is pulled low, the OCP scheme resistors. This is valid for both hiccup mode and latch will be changed to the latch up type, in this mode the up mode. converter will be turned off during Overcurrent or short In 2-phase configuration, the OCP's output depends on circuit. The power needs to be recycled for normal any one channel, which means as soon as one operation. channel goes to overload or short circuit condition the Each phase has its own independent OCP circuitry. output will enter either hiccup or latch-up, dependes on The OCP is performed by sensing current through the status of Hiccup pin. RDS(ON) of low side MOSFET. As shown in Figure 9, an external resistor (RSET) is connected between OCSet pin and the drain of low side MOSFET (Q2) which sets the current limit set point. If using one soft start capacitor in dual configuration for a precise power up the OCP needs to be set to latch mode. 8/28 APU3146 Operation Frequency Selection The optimum operating frequency range for APU3146 is 300KHz per phase, theoretically the APU3146 can be operated at higher switching frequency (e.g. 500KHz). However the power dissipation for IC, which is function of applied voltage, gate drivers load and switching frequency, will result in higher junction temperature of device. It may exceed absolute maximum rating of junction temperature, figure 18 (page 16) shows case temperature versus switching frequency with different capacitive loads. This should be considered when using APU3146 for such application. The below equation shows the relationship Thermal Shutdown Temperature sensing is provided inside APU3146. The trip between IC's maximum power dissipation and Junction threshold is typically set to 140 C. When trip threshold is temperature: J-A exceeded, thermal shutdown turns off both FETs. TherPd = JA mal shutdown is not latched and automatic restart is ini- Where: tiated when the sensed temperature drops to normal Tj: Maximum Operating Junction Temperature (125C) range. There is a 20 C hysteresis in the shutdown thresh- TA: Ambient Temperature (70C) JA = Thermal Impedance of package (84C/W) old. For Tj=125C TA=70C and JA=84C/W Power Good This will result to power dissipation of 650mW, this inThe APU3146 provides a power good signal. The power cludes biasing current for all four external MOSFETs good signal should be available after both outputs have and IC's biasing current. reached regulation. This pin needs to be externally pulled The switching frequency is determined by an external high. High state indicates that outputs are in regulation. resistor (Rt). The switching frequency is approximately Power good will be low if either one of the output voltages inversely proportioned to resistance (see Fig 10). is 10% below the set value. There is only one power good for both outputs. Per channel Switching Frequency vs. RT Frequency Synchronization The APU3146 is capable of accepting an external digital synchronization signal. Synchronization will be enabled by the rising edge at an external clock. Per-channel switching frequency is set by external resistor (Rt). The free running oscillator frequency is twice the per-channel frequency. During synchronization, Rt is selected such that the free running frequency is 20% below the sync frequency. Synchronization capability is provided for both 2output and 2-phase configurations. When unused, the Sync pin will remain floating and is noise immune. 700 650 Switching Frequency in KHz Over-Voltage Protection OVP Over-voltage is sensed through separate VOUT sense pins Vsen1 and Vsen2. A separate OVP circuit is provided for each output. Upon over-voltage condition of either one of the outputs, the OVP forces a latched shutdown on both outputs. In this mode, the upper FET drivers turn-off and the lower FET drivers turn-on, thus crowbaring the outputs. Reset is performed by recycling either Vcc. 600 550 500 450 400 350 300 Error Amplifier 250 The APU3146 is a voltage mode controller. The error am200 plifiers are of transconductance type. In independent mode, 10 20 30 40 50 each amplifier closes the loop around its own output voltRT(Kohm) age. In current sharing mode, amplifier 1 becomes the Figure 10- Switching Frequency versus External Resistor. master which regulates the common output voltage. AmShutdown plifier 2 performs the current sharing function. Both amplifiers are capable of operating with Type III compensa- The outputs can be shutdown independently by pulling the respective soft-start pins below 0.3V. This can be tion control scheme. easily done by using an external small signal transisLow Temperature Start-Up tor. During shutdown both MOSFETs will be turned off. The controller is capable of starting at -40 C ambient During this mode the LDO will stay on. Cycling softtemperature. start pins will clear all fault latches and normal operation will resume. 9/28 APU3146 APPLICATION INFORMATION Soft-Start Programming The soft-start timing can be programmed by selecting Design Example: The following example is a typical application for APU3146, the soft-start capacitance value. The start-up time of the converter can be calculated by using: the schematic is Figure18 on page17. VIN = 12V VOUT(2.5V) = 2.5V @ 10A VOUT(1.8V) = 1.8V @ 10A VOUT = Output voltage ripple 3% of VOUT FS = 300KHz 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 referenced to the voltage on non-inverting pin of error amplifier. For this application, this pin (VP) is connected to reference voltage (VREF). The output voltage is defined by using the following equation: R6 VOUT = VP x 1 + ---(4) R5 ( ) VP2 = VREF = 0.8V When an external resistor divider is connected to the output as shown in Figure 11. VOUT APU3146 VREF R6 Fb R5 VP Figure 11 - Typical application of the APU3146 for programming the output voltage. Equation (4) can be rewritten as: VOUT R6 = R5 x -1 VP ( Will result to: VOUT(2.5V) = 2.5V VREF = 0.8V R9= 2.14K, R5= 1K ) VOUT(1.8V) = 1.8V VREF = 0.8 R7= 1.24K, R8 = 1K 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 can be set more accurately by using low value, precision resistors. Css 25xtSTART (F) ---(5) Where tSTART is the desired start-up time (ms) For a start-up time of 4ms for both output, the soft-start capacitor will be 0.1F. Connect ceramic capacitors at 0.1F from SS1 pin and SS2 pin to GND. Supply VCH1 and VCH2 To drive the high side switch, it is necessary to supply a gate voltage at least 4V grater than the bus voltage. This is achieved by using a charge pump configuration as shown in Figure 12. This method is simple and inexpensive. The operation of the circuit is as follows: when the lower MOSFET is turned on, the capacitor (C1) charges up to VOUT3, through the diode (D1). The bus voltage will be added to this voltage when upper MOSFET turns on in next cycle, and providing supply voltage (VCH1) through diode (D2). Vc is approximately: VCH1 VOUT3 + VBUS - (VD1 + VD2) Capacitors in the range of 0.1F and 1F are generally adequate for most applications. The diode must be a fast recovery device to minimize the amount of charge fed back from the charge pump capacitor into VOUT3. The diodes need to be able to block the full power rail voltage, which is seen when the high side MOSFET is switched on. For low voltage application, schottky diodes can be used to minimize forward drop across the diodes at start up. D1 C3 VOUT3 Regulator D2 VCH1 VBUS C2 C1 Q1 L2 APU3146 HDrv Q2 Figure 12 - Charge pump circuit. 10/28 APU3146 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= (I D1(1-D1)+I D2(1-D2)-2I1I2D1D2) --- (6) 2 1 2 2 Where: 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 recommended. Choose two Poscap from Sanyo 16TPB47M (16V, 47F, 70m ) 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 following relation: i VOUT 1 ; t = Dx ;D= t VIN fS VOUT L = (VIN - VOUT)x ---(7) VINxixfS Where: VIN = Maximum Input Voltage VOUT = Output Voltage i = Inductor Ripple Current fS = Switching Frequency t = Turn On Time D = Duty Cycle VIN - VOUT = Lx For i(2.5V) = 38%(IO(2.5V) ), then the output inductor will be: For i(1.8V) = 30%(IO(1.8V) ), then the output inductor will be: L3 = 1.7H Panasonic provides a range of inductors in different values and low profile for large currents. Choose ETQP6F1R8BFA (1.71H, 14A, 3.3m) both for L3 and L4. For 2-phase application, equation (7) can be used for calculating the inductors value. In such case the inductor ripple current is usually chosen to be between 1040% 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 stability requirements. The ESR of the output capacitor is calculated by the following relationship: (ESL, Equivalent Series Inductance is neglected) VO ESR ---(8) IO Where: VO = Output Voltage Ripple i = Inductor Ripple Current VO = 3% of VO will result to ESR(2.5V) =19.7m and ESR(1.8V) =16m The Sanyo TPC series, Poscap capacitor is a good choice. The 6TPC330M, 330F, 6.3V has an ESR 40m. Selecting two of these capacitors in parallel for 2.5V output, results to an ESR of 20m which achieves our low ESR goal. And selecting four of these capacitors in parallel for 1.8V output, results to an ESR of 10m which achieves our low ESR goal. The capacitors value must be high enough to absorb the inductor's ripple current. Power MOSFET Selection The APU3146 uses four N-Channel MOSFETs. The selections criteria to meet power transfer requirements is based on maximum drain-source voltage (VDSS), gatesource drive voltage (VGS), maximum output current, Onresistance 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). L4 = 1.71H 11/28 APU3146 The gate drive requirement is almost the same for both MOSFETs. Logic-level transistor can be used and caution should be taken with devices at very low VGS to prevent undesired turn-on of the complementary MOSFET, which results a in shoot-through. 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: 2 VDS(OFF) tr + tf ---(9) x x ILOAD T 2 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% PCOND(Upper Switch) = ILOADxRDS(ON)xDx 2 PCOND(Lower Switch) = ILOADxRDS(ON)x(1 - D)x = RDS(ON) Temperature Dependency 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 IRF7457 both for control and synchronous MOSFET. This device provide low on-resistance in a compact SOIC 8-Pin package. The MOSFET have the following data: IRF7457 VDSS = 20V ID = 15A RDS(ON) = 7m The total conduction losses for each output will be: PCON(TOTAL, 2.5V) = PCON(UPPER) + PCON(LOWER) PCON(TOTAL, 2.5V) = 1.0W PCON(TOTAL, 1.8V) = PCON(UPPER) + PCON(LOWER) PCON(TOTAL, 1.8V) = 1.0W The switching loss is more difficult to calculate, even though the switching transition is well understood. The reason is the effect of the parasitic components and switching times during the switching procedures such as turn-on / turnoff delays and rise and fall times. The control MOSFET contributes to the majority of the switching losses in a synchronous Buck converter. The synchronous MOSFET turns on under zero voltage conditions, therefore, the switching losses for synchronous MOSFET can be neglected. With a linear approximation, the total switching loss can be expressed as: 10% VGS td(ON) tr td(OFF) tf Figure 13 - Switching time waveforms. From IRF7457 data sheet we obtain: IRF7457 tr = 16ns tf = 7ns These values are taken under a certain condition test. For more details please refer to the IRF7457 data sheet. By using equation (9), we can calculate the total switching losses. PSW(TOTAL,2.5V) = 0.414W PSW(TOTAL,1.8V) = 0.414W Programming the Over-Current Limit The over-current threshold can be set by connecting a resistor (RSET) from drain of low side MOSFET to the OCSet pin. The resistor can be calculated by using equation (3). The RDS(ON) has a positive temperature coefficient and it should be considered for the worse case operation. RDS(ON) = 7mx1.5 = 10.5m ISET IO(LIM) = 10Ax1.5 = 15A (50% over nominal output current) This results to: RSET = R1=R6=7.8K 12/28 APU3146 Feedback Compensation The APU3146 is a voltage mode controller; the control The ESR zero of the output capacitor is expressed as loop is a single voltage feedback path including error follows: amplifier and error comparator. To achieve fast transient 1 response and accurate output regulation, a compensaFESR = ---(10A) 2xESRxCo tion circuit is necessary. The goal of the compensation network is to provide a closed loop transfer function with VOUT the highest 0dB crossing frequency and adequate phase margin (greater than 45 ). R6 Fb Comp The output LC filter introduces a double pole, -40dB/ Ve E/A decade gain slope above its corner resonant frequency, R5 C9 and a total phase lag of 180 (see Figure 14). The ResoVp=VREF nant frequency of the LC filter is expressed as follows: R4 1 Gain(dB) FLC = ---(10) 2x LOxCO H(s) dB Where: Lo is the output inductor For 2-phase application, the effective output inductance should be used FZ Frequency Co is the total output capacitor Figure 15 - Compensation network without local feedback and its asymptotic gain plot. Figure 14 shows gain and phase of the LC filter. Since we already have 180 phase shift just from the output The transfer function (Ve / VOUT) is given by: Gain Phase ( 0 0dB H(s) = gmx -40dB/decade FLC Frequency -180 FLC Figure14 - gain and phase of LC filter Frequency ) R5 1 + sR4C9 x R6 + R5 sC9 ---(11) The (s) indicates that the transfer function varies as a function of frequency. This configuration introduces a gain and zero, expressed by: R5 |H(s=jx2xFO)| = gmx xR4 ---(12) The APU3146's error amplifier is a differential-input R6+R5 transconductance amplifier. The output is available for 1 DC gain control or AC phase compensation. FZ = ---(13) 2xR 4xC9 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 evi- |H(s)| is the gain at zero cross frequency. dent and can be used to cancel one of the output filter First select the desired zero-crossover frequency (F ): O1 poles. This will be accomplished with a series RC circuit from Comp pin to ground as shown in Figure 15. FO1 > FESR and FO1 (1/5 ~ 1/10)xfS Note that this method requires the output capacitor to have enough ESR to satisfy stability requirements. In general, the output capacitor's ESR generates a zero typically at 5KHz to 50KHz which is essential for an acceptable phase margin. 13/28 APU3146 R4 = VOSC x VIN 1 FO1xFESR R5 + R6 x x gm FLC2 R5 ---(14) Where: VIN = Maximum Input Voltage VOSC = Oscillator Ramp Voltage FO1 = Crossover Frequency FESR = Zero Frequency of the Output Capacitor FLC = Resonant Frequency of the Output Filter R5 and R6 = Resistor Dividers for Output Voltage Programming gm = Error Amplifier Transconductance For V2.5V: VIN = 12V VOSC = 1.25V FO1 = 30KHz FESR = 12KHz For a general solution for unconditional stability for ceramic output capacitor with very low ESR or 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 a voltage-mode controller is shown in Figure 16. To cancel one of the LC filter poles, place the zero before the LC filter resonant frequency pole: FZ 75%FLC 1 FZ 0.75x ---(15) 2 LO x CO For: Lo = 1.71H FZ = 3.56KHz Co = 660F R4 = 2.61K Using equations (13) and (15) to calculate C9, we get: C9 17.18nF; Choose C9 =18nF C12 C10 R7 R8 C11 R6 Zf Fb FLC = 4.75KHz R5 = 1K R6 = 2.14K gm = 2000mho This results to R4=2.61K Choose R4=2.61K VOUT ZIN E/A R5 Comp Ve Vp=VREF Gain(dB) H(s) dB FZ1 FZ2 FP2 FP3 Frequency Figure 16- Compensation network with local feedback and its asymptotic gain plot. In such configuration, the transfer function is given by: Ve 1 - gmZf = VOUT 1 + gmZIN The error amplifier gain is independent of the transconductance under the following condition: gmZf >> 1 and gmZIN >>1 ---(16) Same calcuation For V1.8V will result to: R3 = 2.8K and C8 = 22nF By replacing ZIN and Zf according to Figure 16, the transformer function can be expressed as: 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 = C9xCPOLE 2xR4x C9 + CPOLE The pole sets to one half of switching frequency which results in the capacitor CPOLE: 1 1 CPOLE = xR4xfS 1 xR4xfS C9 fS for FP << 2 H(s) = (1+sR7C11)x[1+sC10(R6+R8)] 1 x sR6(C12+C11) C12C11 1+sR7 C12+C11 x(1+sR8C10) [ ( )] 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: 14/28 APU3146 FP1 = 0 FP2 = FP3 = FZ1 = 1 2xR8xC10 1 ( ) C12xC11 2xR7x C12+C11 1 2xR7xC12 1 2xR7xC11 1 1 FZ2 = 2xC10x(R6 + R8) 2xC10xR6 Cross Over Frequency: VIN 1 FO = R7xC10x x VOSC 2xLoxCo Where: VIN = Maximum Input Voltage VOSC = Oscillator Ramp Voltage Lo = Output Inductor Co = Total Output Capacitors ---(17) 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 (16) regarding transconductance error amplifier. 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 response. The DC gain will be large enough to provide high DC-regulation accuracy (typically -5dB to -12dB). The phase margin should be greater than 45 for overall stability. Based on the frequency of the zero generated by ESR versus crossover frequency, the compensation type can be different. The table below shows the compensation type and location of crossover frequency. Compensator Location of Zero Typical Type Crossover Frequency Output (FO) Capacitor Type II (PI) FPO < FZO < FO < fS/2 Electrolytic, Tantalum Type III (PID) FPO < FO < FZO < fS/2 Tantalum, Method A Ceramic Type III (PID) FPO < FO < fS/2 < FZO Ceramic Method B Table - The compensation type and location of zero crossover frequency. Details are dicussed in application Note AN-1043 which can be downloaded from the IR Web-Site. Compensation for Slave Error Amplfier for 2-Phase Configuration The slave error amplifier is a differential-input transconductance amplifier, in 2-phase configuration 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. The following analysis is valid for both using external current sense resistor and using DCR of inductors. The transfer function of power stage is expressed by: IL2(s) VIN - VOUT = Ve(s) sL2 x VOSC Where: VIN = Input Voltage VOUT = Output Voltage L2 = Output Inductor VOSC = Oscillator Peak Voltage G(s) = ---(18) As shown the transfer function is a function of inductor current. The transfer function for the compensation network is given by equation (19), when using a series RC circuit as shown in Figure 17: D(s) = Ve(s) = RS2 x IL2(s) (g x RR )x(1 +sCsC R ) ---(19) m S1 2 S2 2 2 IL2 L2 Fb2 RS2 Vp2 Comp2 E/A2 Ve R2 RS1 C2 L1 IL1 Figure 17 - The PI compensation network for slave channel. The loop gain function is: H(s)=[G(s) x D(s) x RS2] C x V -V (g x RR )x(1+sR sC ) (sL xV ) H(s)=RS2x m S1 2 S2 2 2 IN 2 OUT OSC 15/28 APU3146 Select a zero crossover frequency for control loop (FO2) 1.25 times larger than zero crossover frequency for voltage loop (FO1): Fo2 1.25%xF01 H(Fo) = gmxRS1xR2x VIN - VOUT =1 2xFoxL2xVOSC ---(20) From (20), R2 can be express as: R2 = 1 gm x RS1 x 2 x FO2 x L2 x VOSC VIN - VOUT ---(21) Set the zero of compensator to be half of FLC(SLAVE), the compensator capacitor, C2, can be calculated as: FLC(SLAVE) = 2 1 L2xCOUT Fz = FLC(SLAVE) 2 C2 = 1 2 x R2 x Fz ---(22) When using the DCR of inductors as current sense element, replace RS1 in equation (21) with DCR value of inductor. 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 by placing the power components. Make all the connections in the top layer with wide, copper filled areas. The inductor, output capacitor and the MOSFET should be as close to each other as possible. This helps to reduce the EMI radiated by the power traces due to the high switching. Place input capacitor near to the drain of the high-side MOSFET. The layout of driver section should be designed for a low resistance (a wide, short trace) and low inductance (a wide trace with ground return path directly beneath it), this directly affects the driver's performance. To reduce the ESR, replace the one input capacitor with two parallel ones. The feedback part of the system should be kept away from the inductor and other noise sources and must be placed close to the IC. In multilayer PCB's, use one layer as power ground plane and have a separate control circuit ground (analog ground), to which all signals are referenced. The goal is to localize the high current paths to a separate loops 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. Switching Frequency vs. Case Temp Case temp (oC) 90 80 100pF 70 1000pF 60 1800pF 50 3300pF 40 30 200 300 400 500 600 700 Freq (KHz) Figure18- Case Temperature versus Switching Frequency at Room Temperature Test Condition: Vin=Vcl=Vch1=Vch2=12V, Capacitors used as loads for output drivers. 16/28 APU3146 C12 1uF L1 12V C1 47uF 1uH C2 47uF D1 BAT54S C3 1uF C4 1uF C5 1uF VCL VcH1 VOUT3 VcH2 Vcc HDrv1 OCSet1 Hiccup VREF Rt 33K R3 C8 20nF 2.8K R4 C9 18nF 2.61K U1 APU3146 VSEN1 Comp1 Comp2 PGood C10 0.1uF SS1 / SD C15 0.1uF 7.8K HDrv2 SS2 / SD LDrv2 C14 2x 47uF 16TPB47M Q2 IRF7457 L3 VSEN1 R6 7.8K 1.8V @ 10A 1.7uH Q3 IRF7457 VSEN1 D2 BAT54A VSEN2 VSEN2 Fb1 Fb2 OCSet2 PGood R1 PGnd1 Sync VP2 R2 LDrv1 C13 1uF C11 0.1uF C16 4x 330uF, 40m 6TPB330M R20 1.24K R21 1K R7 1.24K R8 C17 2x 47uF 16TPB47M Q4 L4 IRF7457 Q5 IRF7457 PGnd2 Gnd VSEN2 1.7uH R22 2.24K R5 1K 1K R9 2.14K 2.5V @ 10A C18 2x 330uF, 40m 6TPB330M R23 1K Figure 19 - Typical application of APU3146. 12V input and two independent outputs. 17/28 APU3146 TYPICAL OPERATING CHARACTERISTICS Test Conditions: VIN=12V, VOUT1=2.5V, IOUT1=0-10A, VOUT2=1.8V, IOUT2=0-10A, Fs=300KHz Figure 20 - Input Supply Ramps up. Ch1: 1.8V, Ch2: 2.5V, Ch3: Input Supply Figure 21 - Input Supply Ramps up/down. Ch1: 1.8V, Ch2: 2.5V, Ch3: Input Supply Figure 22 - Normal condition at No Load. Ch1: HDrv2, Ch2: HDrv1, Ch3 and Ch4: Inductor Currents Figure 23 - Normal condition at 10A Load. Ch1: HDrv2, Ch2: HDrv1, Ch3 and Ch4: Inductor Currents Ch3:ch4: 5A/div Ch3:ch4: 5A/div 18/28 APU3146 TYPICAL OPERATING CHARACTERISTICS Test Conditions: VIN=12V, VOUT1=2.5V, IOUT1=0-10A, VOUT2=1.8V, IOUT2=0-10A, Fs=300KHz Figure 24 - Soft_Start. Ch1: SS2, Ch2: 1.8V, Ch3: SS1, Ch4: 2.5V Figure 26 - Deadband Time (1.8V Output). Ch1: LDrv2, Ch2: HDrv2, Ch3: Switching Node Figure 25 - Soft_Start. Ch1: Vin, Ch2: Vout3(LDO), Ch3: SS2, Ch4: SS2 Figure 27 - Deadband Time (2.5V Output). Ch1: LDrv1, Ch2: HDrv1, Ch3: Switching Node 19/28 APU3146 TYPICAL OPERATING CHARACTERISTICS Test Conditions: VIN=12V, VOUT1=2.5V, IOUT1=0-10A, VOUT2=1.8V, IOUT2=0-10A, Fs=300KHz Figure 28 - Shut Down (Pulling down the SS1 pin). Ch1: HDrv1, Ch2: LDrv1, Ch3: SS1 Figure 30 - High side and Low side Drivers peak Current for 1.8V Output Ch1: HDrv2, Ch2: LDrv2, Ch3: High Side Peak Current, Ch4: Low Side Peak Current Ch3:ch4: 1A/div Figure 29 - Shut Down (pulling down the SS2 pin). Ch1: HDrv2, Ch2: LDrv2, Ch3: SS2 Figure 31 - High side and Low side Drivers peak Current for 2.5V Output Ch1: HDrv1, Ch2: LDrv1, Ch3: High Side Peak Current, Ch4: Low Side Peak Current Ch3:ch4: 1A/div 20/28 APU3146 TYPICAL OPERATING CHARACTERISTICS Test Conditions: VIN=12V, VOUT1=2.5V, IOUT1=0-10A, VOUT2=1.8V, IOUT2=0-10A, Fs=300KHz Figure 32 - Load Transient Response. Ch2: 2.5V, Ch4: Step Load (0-10A) Figure 33 - Load Transient Response. Ch1: 1.8V, Ch3: Step Load (0-10A) Ch3:ch4: 5A/div Ch3:ch4: 5A/div Figure 34 - Power Good Signal Ch1: Input Supply, Ch2: 2.5V Output, Ch3: 1.8V Output, Ch4 : Power Good Signal Figure 35 - Short Circuit Condition (Hiccup Mode). Ch1: SS1 pin, Ch2: SS2 pin, Ch3 and Ch4 : Inductor Currents Ch3:ch4: 10A/div 21/28 APU3146 TYPICAL APPLICATION L1 12V C1 47uF 1uH C2 47uF D1 BAT54S C12 1uF C11 0.1uF C3 1uF C4 1uF C5 1uF VCL VcH1 VOUT3 VcH2 Vcc HDrv1 OCSet1 Hiccup VREF Rt 33K R3 C8 22nF 2.2K C6 120pF R4 C9 12nF 8K U1 APU3146 VSEN1 Comp1 Comp2 PGood C10 0.1uF VSEN2 Fb1 Fb2 12K SS1 / SD SS2 / SD C14 3x 47uF Q2 IRFR3706 L3 1uH, 2m DCR Q3 IRFR3711 R5 HDrv2 LDrv2 1.8V @ 30A 1K D2 BAT54A VSEN R21 1K VSEN C17 3x 47uF OCSet2 C7 82pF PGood R1 PGnd1 VP2 Sync R2 LDrv1 C13 1uF R6 12K Q4 IRFR3706 Q5 IRFR3711 C15 1uF R20 1.24K R7 1.24K R8 1K R9 1K L4 C16 8x 330uF, 40m 6TPB330M C18 1uF 1uH, 2m DCR PGnd2 Gnd Figure 36 - 2-phase operation with inductor current sensing. 12V to 1.8V @ 30A output 22/28 APU3146 TYPICAL APPLICATION L1 12V C1 47uF 1uH C2 47uF D1 BAT54S C12 1uF C11 0.1uF C3 1uF C4 1uF C5 1uF VCL VcH1 VOUT3 VcH2 Vcc HDrv1 OCSet1 Hiccup VREF 33K R3 C8 22nF 2.2K C6 120pF R4 C9 12nF 8K Rt U1 APU3146 VSEN1 Comp1 Comp2 PGood C10 0.1uF VSEN2 Fb1 Fb2 12K SS1 / SD SS2 / SD C14 3x 47uF Q2 IRFR3706 Q3 IRFR3711 L3 R5 1uH D2 BAT54A HDrv2 LDrv2 12K Q4 IRFR3706 Q5 IRFR3711 C16 8x 330uF, 40m 6TPB330M R20 1.24K VSEN R21 1K VSEN R6 1.8V @ 30A 2m R7 1.24K R8 1K C17 3x 47uF OCSet2 C7 82pF PGood R1 PGnd1 VP2 Sync R2 LDrv1 C13 1uF L4 1uH R9 2m PGnd2 Gnd Figure 37 - 2-phase operation with resistor current sensing. 12V to 1.8V @ 30A output 23/28 APU3146 TYPICAL APPLICATION L2 5V 1uH C18 150uF C17 3x 150uF C19 0.1uF D3 BAT54S C20 1uF 12V C1 47uF C13 1uF L1 1uH C2 47uF C3 1uF C4 1uF C5 1uF HDrv1 Vcc OCSet1 Hiccup Rt R3 C8 22nF 2.2K C6 120pF R4 C9 4.7nF 23K Comp1 Comp2 SS1 / SD SS2 / SD Q2 IRFR3706 L3 Q3 IRFR3711 R5 1K HDrv2 LDrv2 PGnd2 Gnd 1.8V @ 30A 1uH, 2m DCR D2 BAT54A C21 1uF C16 8x 330uF, 40m 6TPB330M R20 1.24K R21 1K VSEN2 Fb1 Fb2 OCSet2 PGood C10 0.1uF 12K U1 APU3146 VSEN1 C7 27pF PGood R1 PGnd1 VP2 VREF 33K LDrv1 C11 0.1uF C14 3x 47uF VCL VcH1 VOUT3 VcH2 Sync R2 D1 BAT54S C12 1uF Q4 IRFR3706 R6 12K Q5 IRFR3711 R9 1K C22 1uF R7 1.24K R8 1K L4 1uH, 2m DCR Figure 38 - Typical application of APU3146 using 5V and 12V supplies to generate single output voltage. 1.8V @ 30A using inductor sensing. 24/28 APU3146 TYPICAL APPLICATION L2 1uH 5V C18 150uF C17 3x 150uF D3 BAT54S C20 1uF 12V C1 47uF C19 0.1uF C13 1uF L1 1uH C2 47uF C3 1uF C4 1uF C5 1uF HDrv1 Vcc OCSet1 Hiccup R3 C8 22nF 2.2K C6 120pF R4 C9 4.7nF 23K Rt Comp1 Comp2 SS1 / SD SS2 / SD Q2 IRFR3706 Q3 IRFR3711 C11 0.1uF L3 1uH R5 1.8V @ 30A 2m HDrv2 LDrv2 C16 8x 330uF, 40m 6TPB330M R20 1.24K D2 BAT54A R21 1K VSEN2 Fb1 Fb2 OCSet2 PGood C10 0.1uF 15K U1 APU3146 VSEN1 C7 27pF PGood LDrv1 R1 PGnd1 VP2 VREF 33K C14 3x 47uF VCL VcH1 VOUT3 VcH2 Sync R2 D1 BAT54S C12 1uF R7 1.24K R8 1K R6 10K Q4 IRFR3706 Q5 IRFR3711 L4 R9 1uH 3m PGnd2 Gnd Figure 39 - Typical application of APU3146. 1.8V @ 30A output with 5V and 12V input and different input current setting. (5V @ 5A and 12V @ 3A) 25/28 APU3146 TYPICAL APPLICATION L1 5V C1 47uF 1uH C2 47uF D1 BAT54S C12 1uF C3 1uF C4 1uF C5 1uF VCL VcH1 VOUT3 HDrv1 Vcc OCSet1 Hiccup VREF Rt 33K R3 C8 8.2nF 6K C6 47pF R4 C9 4.7nF 15K C7 Comp1 Comp2 SS1 / SD C15 0.1uF 10K HDrv2 SS2 / SD LDrv2 C14 3x 330uF 6TPB330M Q2 IRF7457 L3 1.8V @ 10A 1uH Q3 IRF7460 C16 4x 330uF, 40m 6TPB330M R20 1.24K VSEN1 D2 BAT54A VSEN2 Fb1 Fb2 OCSet2 PGood C10 0.1uF R1 U1 APU3146 VSEN1 27pF PGood LDrv1 C13 1uF PGnd1 Sync VP2 R2 VcH2 C11 0.1uF R21 1K R7 1.24K R8 R6 8.5K R5 C17 3x 330uF 6TPB330M Q4 1/2 IRF7910 L4 Q5 1/2 IRF7910 1K R9 2.14K 3.3uH PGnd2 Gnd 1K 2.5V @ 5A C18 2x 330uF, 40m 6TPB330M R22 2.14K VSEN2 R23 1K Figure 40 - Single 5V input and two independent outputs. 26/28 APU3146 TYPICAL APPLICATION 12V 5V C1 47uF L1 1uH C2 47uF C3 1uF C4 1uF VCL VcH1 VOUT3 C5 1uF OCSet1 Hiccup Rt 33K R3 C8 8.2nF 6K 4.7nF 15K Comp2 PGood SS1 / SD C15 0.1uF VSEN2 Fb1 Fb2 HDrv2 OCSet2 C7 27pF C10 0.1uF Q2 IRF7457 L3 SS2 / SD LDrv2 1.8V @ 10A 1uH Q3 IRF7460 D2 BAT54A U1 APU3146 VSEN1 Comp1 C6 47pF R4 C9 10K Sync VREF R2 LDrv1 R1 C14 3x 330uF 6TPB330M C16 4x 330uF, 40m 6TPB330M R20 1.24K PGnd1 VP2 PGood VcH2 HDrv1 Vcc C13 1uF VSEN1 R21 1K R7 1.24K R8 C17 3x 330uF 6TPB330M R6 5.1K Q4 IRF7457 Q5 IRF7460 PGnd2 Gnd L4 3.3uH R22 2.14K R5 1K 1K R9 2.14K 2.5V @ 5A C18 2x 330uF, 40m 6TPB330M VSEN2 R23 1K Figure 41 - Typical application of APU3146. 5V input, 12V drive and two independent outputs. 27/28 APU3146 TYPICAL APPLICATION 3.3V L1 5V C1 47uF 1uH C2 47uF C3 1uF C4 1uF C5 1uF VCL VcH1 VOUT3 VcH2 HDrv1 Vcc OCSet1 LDrv1 Hiccup VREF R2 R3 C8 4.7nF 15K C6 27pF R4 C9 5.6nF 8.2K C7 U1 Rt 33K APU3146 Comp1 Comp2 PGood SS1 / SD C15 0.1uF R1 8.5K SS2 / SD C11 0.1uF C14 2x 330uF 6TPB330M Q2 1/2 IRF7910 L3 LDrv2 C16 2x 330uF, 40m 6TPB330M R20 2.14K VSEN1 R21 1K Fb1 Fb2 HDrv2 2.5V @ 5A 3.3uH Q3 1/2 IRF7910 D2 BAT54A VSEN1 VSEN2 OCSet2 27pF PGood C13 1uF PGnd1 Sync VP2 C10 0.1uF D1 BAT54S C12 1uF R7 2.14K R8 1K R6 8.5K C17 2x 330uF Q4 6TPB330M L4 1/2 IRF7910 Q5 1/2 IRF7910 PGnd2 Gnd R5 R9 1.24K 2.2uH 1K 1.8V @ 5A C18 2x 330uF, 40m 6TPB330M R22 1.24K VSEN2 R23 1K Figure 42 - Typical application of APU3146. 5V to 2.5V and 3.3V to 1.8V inputs and two independent outputs. 28/28