US3034 8 PIN PWM SWITCHER CONTROLLER IC PRELIMINARY DATASHEET FEATURES DESCRIPTION 8 pin SOIC Switching Controller with HICCUP Current Limiting Reduces Diode Power Dissipation to Less than 1% of Normal Operation Soft Start Capacitor allows for smooth Output Voltage ramp up On board MOSFET driver Fastest transient response of any controller method. ( 0 to 100% Duty Cycle in 100 nS ) 1% internal voltage reference Internal Under Voltage Lockout protects MOSFET during start-up The US3034 IC provides an 8 pin low cost switching controller with true short circuit protection all in a compact 8 pin surface mount package, providing a low cost switching solution for dual supply processor applications that require switching regulator for the 3.3V supply such as the applications with AGP on board. Typically in these applications a dual supply regulator converts 5V to 3.3V for I/O supply and a jumper programmable supply of 1.25V to 3.5V for CORE supply . The IC uses an internal regulator generated from the 12V supply to power the controller as well as the 12V supply to drive the power MOSFET, allowing a low cost N channel MOSFET to be used. The IC also includes an error comparator for fast transient response, a precise voltage reference for setting the output voltage as well as a direct drive of the MOSFET for the minimum part count. APPLICATIONS Dual supply low voltage processor applications, such as: P55C,CYRIX M2, POWER PC and AMD K6 Simple 5V to 3.3V switcher for Pentium with AGP or Pentium II applications TYPICAL APPLICATION C6 8 7 6 5 C8 SS CS+ CS- Gnd US3034 Drv V12 Vfb Vhyst 1 2 3 4 12V C3 R8 R3 R7 C5 L2 R1 R6 Vout C7 L1 5V Q2 C1 C2 C4 R2 R4 D1 R5 3034app1-1.0 Typical application of US3034 Notes: P55C,Pentium II are trade marks of Intel Corp. K5 & K6 are trade marks of AMD corp. Cyrix 6X86L,M1,M2 are trade marks of Cyrix Corp. Power PC is trade mark of IBM Corp. PACKAGE ORDER INFORMATION TA (°C) 0 TO 70 Rev. 1.8 1/13/99 8 PIN PLASTIC SOIC (S) US3034CS 4-1 US3034 ABSOLUTE MAXIMUM RATINGS V12 Supply Voltages ............................................................. 20V F.B Pin Voltages........................................................ -0.3V to 5V Storage Temperature Range ................................. -65 TO 150°C Operating Junction Temperature ............................... 0 TO 150°C PACKAGE INFORMATION 8 PIN PLASTIC SOIC (S) TOP VIEW Drv 1 8 SS V12 2 7 CS+ Vfb 3 6 CS- Vhyst 4 5 Gnd θJA =160°C/W ELECTRICAL SPECIFICATIONS Unless otherwise specified the following specification applies over V12 =12V, and TA =0 to 70°C. Low duty cycle pulse testing are used which keeps junction and case temperatures equal to the ambient temperature. PARAMETER F.B Voltage Initial Accuracy F.B Voltage Total Variation F.B Voltage Line Regulation F.B Input Bias Current Min On Time SYM VFB IFB Min Off Time Vhyst pin output-HI Vhyst pin output-LO Supply Current Maximum Duty Cycle Minimum Duty Cycle Gate Drive Rise/Fall Time C.L Threshold Current C.S Comp Common Mode Soft Start Current 4-2 I12SW DMAX DMIN VGATE ICL TEST CONDITION TJ =25°C VFB =1.25V VFB is sq wave with 300 ns on time and 2 uS off time VFB is sq wave with 300 ns off time and 2 uS on time ISOURCE =500uA, VFB =1.5V ISINK =500uA, VFB =1V VFB =1V VFB =1V VFB =1.5V Load=IRL3303 C.S+ , C.S- from 1.3V to 3.7V VCS+ = VCS- MIN 1.237 1.225 TYP 1.250 1.250 0.2 800 UNITS V V % uA nS 800 nS -1 MAX 1.262 1.275 +1 11 1 10 100 0 70 20 0 4.5 10 V V mA % % nS uA V uA Rev. 1.8 1/13/99 US3034 PIN DESCRIPTIONS PIN # 3 6 7 5 1 4 2 8 PIN SYMBOL PIN DESCRIPTION A resistor divider from this pin to the output of the switching regulator and ground sets the VFB Core supply voltage. This pin is connected to the minus side of the external current sense resistor. An internal C.Scurrent source together with an external resistor in series with this pin programs the current limit threshold voltage. This voltage divided by the external current sense resistor sets the current limit threshold. This pin is connected to the plus side of the external current sense resistor. A resistor in C.S+ series with this pin and a capacitor connected between this pin and pin 6 provides a high frequency filtering for the noise spikes of turn on and turn off switching. This pin is connected to the IC substrate and must be connected to the lowest potential Gnd in the system. The PWM output of the switching controller. This pin is a totem pole drive that is conDrv nected to the gate of the power MOSFET. A resistor may be placed from this pin to the gate in order to reduce switching noise. A resistor and a 10pF capacitor is connected from this pin to the VFB1 pin to set the VHYST output ripple voltage for the switching regulator. This pin supplies the voltage to the PWM drive and hysterises circuitry and it is conV12 nected to the 12V supply. A 1 uF, high frequency capacitor must be connected from this pin to ground to provide the peak current for charging and discharging of the MOSFET. This pin provides the soft start for the regulator during power up. It also sets a long off S.S time when the converter goes into current limiting, providing low duty cycle for the catch diode allowing it to survive during short circuit. BLOCK DIAGRAM V12 2 Vhyst 4 Vfb 3 5V Reg Drv 1 Gnd 5 UVLO R 20uA CS6 PWM Control 1.25V Vref 3R S.S. / Hiccup Control 3034blk1-1.1 CS+ 7 SS 8 Figure 1 - Simplified block diagram of the US3034 Rev. 1.8 1/13/99 4-3 US3034 TYPICAL APPLICATION Pentium Core Supply Application (US3034 and US3033 Dual Layout) Low Cost 4 Bit VID ** R9 12V C6 8 7 6 5 C8 ** R9 can be eliminated if dual layout with US3033 is not desired. SS/ CS+/ CS-/ Gnd V12 Drv2 Vfb2 U1 Drv V12 Vfb Vhyst 1 2 3 4 R8 R7 C3 R3 C5 L2 R1 R6 Vout C7 L1 5V Q2 C1 R4 C2 C4 R2 3034app2-1.0 R5A R5B R5C R5D R5E D1 JP1 1 2 3 4 5 6 7 8 Figure2- Typical application of US3034 in a flexible motherboard with the 4 bit VID output voltage selection. This circuit is done using a dual layout with the US3033 part . The advantage of this circuit is that it uses a single jumper that programs the output voltage in 16 steps with 0.1V steps from 2V to 3.5V, designed for Intel P55,P54 AMD K5 & K6 as well as Cyrix M1 and M2 applications. JP1 1-2 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 4-4 JP1 3-4 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 JP1 5-6 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 JP1 7-8 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Output Voltage 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 0 = Jumper block is installed. 1 = Jumper block is not installed. Rev. 1.8 1/13/99 US3034 Pentium Core Supply Application Parts List (US3034 and US3033 Dual Layout) Low Cost 4 Bit VID Ref Desig U1 Q2 Description LDO/Switcher IC MOSFET Qty 1 1 D1 Schottky Diode 1 L2 Inductor 1 L1 R1 R2 R3 R4A * R4B * R5A R5B R5C R5D R5E R6 R7 R8 R9 C1 C2 C3 C4 C5 C7 C8 C6 HS1 HS2 Inductor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Heat Sink Heat Sink 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4 1 1 1 1 Part # US3034CS ( 8 pin SOIC) IRL3303 (TO220) IRL3103S (TO263) (note 1) MBR1045CT (TO220) MBRB1545CT (TO263) (note1) Core:T50-18,L=4 uH Turns: 10T, 18 AWG L=2 uH 22 ohm,5%, SMT 1206 size 10 ohm, 5%, SMT 1206 size 324 kohm,1%, SMT 0805 size 806 ohm,1%, SMT 0805 size 90.9 kohm,1%, SMT 0805 size 1.24 kohm,1%, SMT 0805 size 2.49 kohm,1%, SMT 0805 size 4.99 kohm,1%, SMT 0805 size 10 kohm,1%, SMT 0805 size 1.30 kohm,1%, SMT 0805 size 5 miliohm,5%, 2W 4.99 kohm,1%, SMT 0805 size 4.7 kohm,5% for US3034, open for 3033 open for US3034, 10 ohm for US3033 6MV1500GX, 1500uF,6.3V, Elect 6MV1500GX, 1500uF,6.3V, Elect 1 uF,Ceramic, SMT 0805 size 470 pF,Ceramic, SMT 0805 size 10 pF,Ceramic, SMT 0805 size 6MV1500GX, 1500uF,6.3V, Elect 0.047 uF for 3034 , 0.1uf for 3033 4700pF for US3034, open for US3033 For MOSFET , 577002 For Schottky Diode , 577002 Manufacturer Unisem International Rectifier Motorola Micro Metal (core) Sanyo Sanyo Sanyo Sanyo Aavid Aavid * R4 is a parallel combination of R4A and R4B. Note 1: For the applications where it is desirable to eliminate the heat sink, the IRL3103S for Q2 and MBR1545CT for D2 in TO263 packages with minimum of 1" square copper pad can be used. Rev. 1.8 1/13/99 4-5 US3034 TYPICAL APPLICATION 5V to 3.3V for Pentium Application with AGP or Pentium II Application without ATX power supply Switching mode Operation. (US3034 and US3033 Dual Layout) R9 12V C6 8 7 6 5 C8 SS/ CS+/ CS-/ Gnd V12 Drv2 Vfb2 U1 Drv V12 Vfb Vhyst 1 2 3 4 C3 R8 R3 R7 C5 L2 R1 R6 Vout C7 L1 5V Q2 C2 C1 C4 R2 R4 D1 R5 3034app3-1.0 Figure4- The circuit in figure 4 is the application of the US3034 which is done using a dual layout with US3033 in a switching mode only. This circuit can be used to generate a low cost 5V to 3.3V for either Pentium application with AGP socket or in Pentium II applications where it is desirable to generate an accurate on board 3.3V supply. Ref Desig U1 Q2 Description LDO/Switcher IC MOSFET Qty 1 1 D1 Schottky Diode 1 L2 Inductor 1 L1 R1 R9 R2 R3 R4 R5 R6 R7 R8 C1,2 C3 C4 C5 C6 C7 C8 HS1 HS2 Inductor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Heat Sink Heat Sink 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 2 1 1 1 Part # US3034CS ( 8 pin SOIC) IRL3303 (TO220) IRL3103S (TO263) (note 1) MBR1045CT (TO220) MBRB1545CT (TO263) (note1) Core:T50-18,L=4 uH Turns: 10T, 18 AWG L=2 uH 22 ohm,5%, SMT 1206 size open for US3034, 10 ohm for US3033 10 ohm, 5%, SMT 1206 size 249 kohm,1%, SMT 0805 size 1 kohm,1%, SMT 0805 size 576 ohm,1%, SMT 0805 size 5 miliohm,5%, 2W 4.99 kohm,1%, SMT 0805 size 4.7 kohm,5% for US3034, open for 3033 6MV1500GX, 1500uF,6.3V, Elect 1 uF,Ceramic, SMT 0805 size 470 pF,Ceramic, SMT 0805 size 10 pF,Ceramic, SMT 0805 size 4700pF for US3034, open for US3033 6MV1500GX, 1500uF,6.3V, Elect 0.047 uF for 3034 , 0.1uf for 3033 For MOSFET , 577002 For Schottky Diode , 577002 Manufacturer Unisem International Rectifier Motorola Micro Metal (core) Sanyo Sanyo Sanyo Sanyo Aavid Aavid Note 1: For the applications where it is desirable to eliminate the heat sink, the IRL3103S for Q2 and MBR1545CT for D2 in TO263 packages with minimum of 1" square copper pad can be used. 4-6 Rev. 1.8 1/13/99 US3034 TYPICAL APPLICATION 5V to 3.3V with lossles short cicuit protection(output UVLO detection). 8 7 6 5 C8 R7 SS CS+ CS- Gnd US3034 Drv V12 Vfb Vhyst 12V C6 R6 1 2 3 4 C3 R3 C5 L2 R1 Vout C7 L1 5V Q2 C1 C2 C4 R2 R4 D1 R5 3034app5-1.1 Figure 5- The circuit in figure 5 is designed to provide lossles output short detection by detecting the dc voltage across the inductor and shutting down the MOSFET and entering HICCUP mode. Note that the current limit point is a function of the inductor resistance and in this application with approximately 8 mil ohm resistance the peak C.L is set at 10A. See application note on how to set the current limiting threshold. Ref Desig U1 Q2 Description Switcher IC MOSFET Qty 1 1 D1 Schottky Diode 1 L2 Inductor 1 L1 R1,2 R3 R4 R5 R7 R6 C1 C2 C3 C5 C6 C7 C8 Inductor Resistor Resistor Resistor Resistor Resistor Resistor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor Capacitor 1 2 1 1 1 1 1 1 1 1 1 1 2 1 Rev. 1.8 1/13/99 Part # US3034CS ( 8 pin SOIC) IRL3303 (TO263) PBYR735(Axial Thr Hole pkg) PBYR1035B(SMT, TO263 pkg) Core:T50-18,L=4 uH Turns: 7T, 18 AWG L=1 uH 10 ohm,5%, SMT 182 kohm,1%, SMT 1 kohm,1%, SMT 576ohm,1%, SMT 3.83 kohm,1%, SMT 1 kohm,1% , SMT 470uF, Elect 6MV1000GX, 1000uF,6.3V, Elect 1 uF,Ceramic, SMT 10 pF,Ceramic, SMT 0.1 uF 6MV1000GX, 1000uF,6.3V, Elect 0.047 uF Manufacturer Unisem International Rectifier Motorola Micro Metal (core) Sanyo Sanyo Sanyo 4-7 US3034 APPLICATION INFORMATION Introduction The US3034 device is an application specific product designed to provide an on board switching supply for the new generation of microprocessors requiring separate Core and I/O supplies where the load current demand from the I/O supply requires this regulator to also be a switching regulator such as the motherboard applications with AGP slot or the Pentium II with on board 5V to 3.3V converter. The US3034 provides an easy and low cost switching regulator solution for Vcore and 3.3V supplies with true short circuit protection. Switching Controller Operation The operation of the switching controller is as follows : after the power is applied, the output drive pin, "Drv" goes to 100% duty cycle and the the current in the inductor charges the output capacitor causing the output voltage to increase. When output reaches a pre-programmed set point the feedback pin "Vfb" exceeds 1.25V causing the output drive to switch low and the "Vhyst" pin to switch high which jumps the feedback pin higher than 1.25V resulting in a fixed output ripple which is given by the following equation : dVo=(Rt/Rh)x11 Where: Rt=Resistor connected from Vout to the Vfb pin of US3034 Rh=Resistor connected from Vfb pin to Vhyst pin. For example, if Rt=1k and Rh=422k, then the output ripple is : dVo=(1/422)x11=26mV The advantage of fixed output ripple is that when the output voltage changes from 2V to 3.5V, the ripple voltage remains the same which is important in meeting the Intel maximum tolerance specification. Soft Start The soft start capacitor must be selected such that during the start up when the output capacitors are charging up, the peak inductor current does not reach the current limit treshold. A minimum of 0.1uF capacitor insures this for most applications. During start up the soft start capacitor is charged up to approximately 6V keeping the output shutdown before an internal 10uA current source start discharging the soft start capacitor which slowly ramps up the inverting input of the PWM comparator, Vfb. This insures the output to ramp up at the same rate as the soft start cap thereby limiting the input current. For example, with 0.1uF and the 10uA internal current source the ramp up rate is (∆V/ ∆t)=I/Css = 10/ 0.1=100V/Sec or 0.1V/mSec. Assuming that the output capacitance is 6000uF, the peak input current will be: Iin(pk)=Css*(∆V/ ∆t)=6000uF*(0.1V/mSec)=0.6A 4-8 The soft start capacitor also provides a delay in the turn on of the output which is given by: Td=CSS*K Where K=30 ms/uF For example for CSS=0.1uF, Td=0.1* 30=3 ms Switcher Current Limit Protection The US3034 uses an external current sensing resistor and compares the voltage drop across it to a programmed voltage which is set externally via a resistor (RcL) placed between the “CS-” terminal of the IC and Vout. Once the voltage across the sense resistor exceeds the threshold, the soft start capacitor pulls up to 12V, pulling up the inverting pin of the error comparator higher than non inverting which causes the external MOSFET to shut off. At this point the C.S comparator changes its state and pulls the soft start capacitor to Vcc which is 12V and shutting the PWM drive. After the output drive is turned off, an internal 10uA current source slowly discharge the soft start capacitor to approximately 5.7V, before the output starts to turn back on causing a long delay before the MOSFET turns back on. This delay causes the catch diode to cool off between the current limit cycles allowing the converter to survive a short circuit condition. An example is given below as how to select the current limiting components. Assuming the desired current limit point is set to be 20A and the current sense resistor Rs=5mΩ, then the current limit programming resistor,RcL is calculated as : Vcs=IcL*Rs=20*0.005=0.1V RcL=Vcs/Ib=(0.1V)/(20uA)=5kΩ Where: Ib=20uA is the internal current source of the US3034 The peak power dissipated in the C.S. resistor is : Ppk=(IcL^2)*Rs=20^2*0.005=2W However, the average power dissipated is much lower than 2W due to the long off time caused by the hiccup circuit of 3034. The average power is in fact the short circuit period divided by the short circuit period plus the off time or "hiccup" period. For example, if the short circuit lasts for TSC=100uSec before the 3034 enters hiccup, the average power is calculated as : Pave=0.5*Ppk*DSC Where: DSC=TSC/THCP THCP=CSS*M Where M=200 ms/uF & CSS, is the soft start capacitor For example for CSS=0.1uF & TSC=500uSec=0.5mS THCP=0.1* 200=20 ms Pave=0.5*2*(0.5/20)=25 mW Without "hiccup" technique, the power dissipation of the resistor is 2W. Rev. 1.8 1/13/99 US3034 Switcher Output Voltage Setting The output voltage can be set using the following equations. Assuming , Vo=3.38V and the selected output ripple is ≈ 1.3%(44mV) of the output voltage, a set of equations are derived that selects the resistor divider and the hysterises resistor. Assuming, Rt=1kΩ , 1% Rh=(11*Rt)/∆Vo Where: Rt=Top resistor of the resistor divider Rh=Hysterises resistor connected between pins 3 and 4 of the US3034 ∆Vo=Selected output ripple (typically 1% to 2% of output voltage) Assuming, ∆Vo=44mV Rh=(11*1000)/0.044=250 kΩ Select Rh=249 kΩ , 1% The bottom resistor of the divider is then calculated using the following equations: Rb=Rt/X Where: Rb=Bottom resistor of the divider X=[(Vo + (∆Vo/2))/Vref] - 1 Vref=1.25 V typ. X=[(3.38+ (0.044/2))/1.25] - 1 = 1.72 Rb=1000/1.72=580 Ω Select Rb=576 Ω , 1% Frequency Calculation The US3034 frequency of operation is calculated using the following formula: Fs=[(Vo*(1-D)*ESR)]/(L*∆Vo) (MHz) Where: Vo=Output voltage (V) D=Duty cycle ESR=Output capacitor ESR (V) L=Output inductance (uH) ∆Vo=Output ripple voltage (V) For our example: D≈(Vo + Vf)/Vin Where, Vf=Forward voltage drop of the Schotky diode D=(3.38 + 0.5)/5=0.78 The ESR=18mΩ for 2 of the Sanyo 1500uF, 6MV1500GX caps. If L=3.5uH then, Fs is calculated as follows: Fs=[(3.38*(1-0.78)*0.018)]/(3.5*0.044)= 0.087 Mhz = 87 kHz Rev. 1.8 1/13/99 4-9