SC1175 versatile phase, synchronous, voltage mode controller that used
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Power Dual Synchronous DC/DC Controller With Current Sharing Circuitry
SC1175 versatile phase, synchronous, voltage mode controller that used distinct ways. First, SC1175 ideal applications where point output power exceeds single input power budget. Alternatively, SC1175 used dual switcher. SC1175 features temperature compensated voltage reference, over current protection with fold-back internal level-shifted, high-side drive circuitry. current sharing configuration, SC1175 produce single output voltage from separate voltage sources (which different voltage levels) while maintaining current sharing between channels. Current sharing programmable allow loading each input supply required application. dual switcher configuration, feedback paths provided independent control separate outputs. device will provide regulated output from flexibly configured inputs (3.3V, 12V), provided present VCC. switchers 180° phase minimize input output ripple.
SC1175
Features
300kHz fixed frequency operation Soft Start Enable function Power Good output provided Over current protection with fold-back Phase-shifted switchers minimize ripple High efficiency operation, >90% Programmable output(s) 1.25V Industrial temperature range SOIC package
Phase, Current Sharing Controller Flexible, same separate Programmable current sharing Combined current limit with fold-back phases operating opposed ripple reduction Thermal distribution multi-phase output
Applications
Graphics cards Memory Peripheral add-in card SSTL Termination Dual-Phase power supply Power supplies requiring outputs
Independent Controllers Flexible, same separate Independent control each channel Independent separate current limit phases operating opposed ripple reduction same used)
Typical Application Circuit
Channels with Current Sharing
Revision 7/31/2000
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SC1175
POWER MANAGEMENT Absolute Maximum Rating
Parameter PGND Thermal Resi stance Juncti Thermal Resi stance Juncti Ambi mbol Limits -0.3 -0.3 nits
+150
Operati Ambi Temperature Range Operati Juncti Temperature Range
Storage Temperature Range Lead Temperature (Solderi
TSTG TLEAD
Electrical Characteristics
Unless Specified: 4.75 5.25V, PGND (CS(+) CS(-)) 60mV 25°C
AMETER Output Voltage Supply Voltage Supply urrent Reference Load Regulati Reference Regulati Output Regulati (AOL) urrent Voltage Osci llator Frequency Osci llator ycle urrent urrent Source urrent Source urrent PGND 3.5V PGND 1.75V BSTH 5.0V BSTH 2.5V 0.3A VOSENSE ITION 2A(1), VOUT 2.75V
1.2375±1
2.65
2.75 1.25
2.85
1.2625±1
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SC1175
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless Specified: 4.75 5.25V, PGND (CS(+) CS(-)) 60mV 25°C
AMETER urrent urrent Source urrent Source urrent Soft Start harge urrent Soft Start Enable Soft Start Soft Start Transi on(2) Power Good ndow(3) Fold Back urrent Fold Back Voltage Knee Input urrent
ITION PGND 3.5V PGND 1.75V BSTL BSTL 2.5V
%VOUT VOUT
duty cycle 100% duty cycle Synchronous mode VOUT ILIM -IN1, +IN2, -IN2 1.25
NOTES: Specification refers application circuit. soft start sources 25µA external capacitor. converter operates synchronous mode above soft start transition threshold asynchronous mode below Power good open collector pulled when output voltage outside ±10% window. This device sensitive. standard handling precautions required.
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SC1175
POWER MANAGEMENT Configuration Ordering Information
EVIC E(1) 1175C SW.TR 1175EVB-1 SO-20 URRENT SHARE VERSION EVALUATION BOARD HANNEL VERSION EVALUATION BOARD
1175EVB-2
Notes: Only available tape reel packaging. reel contains 1000 devices
Marking Information Descriptions
EXPANDED DESCRIPTION (VREF) Internal 1.25V reference Connected input master channel error amplifier. (+IN) Input slave channel error amplifier. Connected 1.25V reference (Pin independent channel configuration. (-IN2, -IN1) Inputs close loop error amplifiers. Works feedback inputs (For both modes). (VCC) chip supply voltage. maximum, 10mA typical. Needs ceramic multilayer decoupling capacitor (Pin 20). 6,15, (CL2-, CL2+, CL1+, CL1-) Pins current limit amplifiers both channels. Connected output current sense resistors. Compares that sense voltage internal 75mV reference. Needs filter noise rejection. (BST2, BST1) signal. Supply high side driver. connected high enough voltage source. Usually connected bootstrap circuit. (DH2, DH1) signal (Drive High). Gate drive MOSFETs. Requires small series resistor.
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yyww Datecode (Example: 9908) xxxx Semtech (Example: 90101)
(DL2, DL1) signal (Drive Low). Gate drive bottom MOSFETs. Requires small series resistor. (PGND) Power GND. Return gate drive currents. (BSTC) Supply bottom MOSFETs gate drive. (SS/ENA) Soft start pin. Internal current source connected external capacitor. Inhibits chip pulled down. (PWRGD) Power good signal. Open collector signal Turns output voltage outside power good window. (GND) Analog GND. Return analog signals bias chip.
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SC1175
POWER MANAGEMENT Block Diagram
NOTES Block (top) Master Block (bottom) Slave current sharing configuration. independant operation there Master Slave.
Applications Information
Theory Operation
Main Loop(s)
SC1175 dual, voltage mode synchronous Buck controller, separate channels identical share only supply pins (Vcc GND), output driver ground (PGND) pre-driver supply voltage (BSTC). They also share common oscillator generating sawtooth waveform channel inverted sawtooth channel Each channel current limit comparator. Channel positive input error amplifier internally connected Vref. Channel both inputs error amplifier uncommitted available externally. This allows SC1175 operate distinct modes. independent channels with either common different input voltages different output voltages. channels each have their voltage feedback path from their
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output. this mode, positive input error amplifier connected externally Vref. application uses common input voltage, sawtooth phase shift between channels provides some measure input ripple current cancellation. channels operating current sharing mode with common output voltage either common input voltage different input voltages. this mode, channel operates voltage mode Buck controller, before, error monitors amplifies difference voltage across output current sense resistors channel channel (Master Slave) adjusts Slave duty cycle match output currents. Because finite gain offsets loop, resistor ratio perfect current matchwww.semtech.com
SC1175
POWER MANAGEMENT
Theory Operation (Cont.) 1:1. Master Slave channels still have their current limits, identical independent channel case. Power Good controller provides power good signal. This open collector output, which pulled output voltage outside power good window. Soft Start/Enable Soft Start/Enable (SS/ENA) serves several functions. held below Soft Start Enable threshold, both channels inhibited. will low, turning FETs. Between Soft Start Enable threshold Soft Start threshold, duty cycle allowed increase. Soft Start threshold, maximum duty cycle reached. practical applications error amplifier will controlling duty cycle before Soft Start threshold reached. avoid boost problems during startup current share mode, both channels start asynchronous mode, bottom body diode used recirculating current during time. When SS/ENA reaches Soft Start Transition threshold, channels begin operating synchronous mode improved efficiency. soft start sources approximately 25uA soft start timing selection appropriate soft start capacitor value. formula
(pull VSLAVE
100W being value resistors connecting pins output sense resistors. estimated voltage drop across MOSFETs 0.1V. Positive values negative (pull-up) +20KW then place 20WK resistor (pull-up) -20KW then place 20KW that offset resistor been fixed, need maximum current each channel. Selection RSENSE master channel: (mohms) RSENSE 72mV master Selection RSENSE slave channel: (mohms) RSENSE 48mV master errors will minimized power components have been sized proportionately maximum currents. Independent Channels Calculation current limiting resistors. There need offset resistor independent channels mode, only sense resistors used: Selection RSENSE channel (mohms) RSENSE 72mV Selection RSENSE channel (mohms) RSENSE 72mV
SENSE RESISTOR SELECTION
Current Sharing Mode Calculation three programming resistors achieve sharing. Three resistors will determine current sharing load line. First offset resistor will ensure that load line crosses origin each channel) sharing light current. pull resistor from bias (VCC chip) will used. duty cycle slave channel (below 50%), pull will high duty cycle slave channel (above 50%), pull will
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SC1175
POWER MANAGEMENT Typical Characteristics Channels with Current Sharing
Figure VOUT IIN(5V) IIN(12V) with applied load. Soft start capacitor 10nF.
Descriptions
Ch1: VOUT Ch2: IIN(5V) (1A/Div) Ch4: IIN(12V) (1A/Div) IOUT: 4.004 Amps
Figure VOUT IIN(5V) IIN(12V) with removed load. Soft start capacitor 10nF.
Ch1: VOUT Ch2: IIN(5V) (1A/Div) Ch4: IIN(12V) (1A/Div) IOUT: 4.004 Amps
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SC1175
POWER MANAGEMENT Typical Characteristics Channels with Current Sharing (Cont.)
Figure VOUT IIN(5V) IIN(12V) with applied load. Soft start capacitor 10nF.
Ch1: VOUT Ch2: IIN(5V) (2A/Div) Ch4: IIN(12V) (2A/Div) IOUT: Amps
Figure VOUT IIN(5V) IIN(12V) with removed load. Soft start capacitor 10nF.
Ch1: VOUT Ch2: IIN(5V) (2A/Div) Ch4: IIN(12V) (2A/Div) IOUT: Amps
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SC1175
POWER MANAGEMENT Typical Characteristics Channels with Current Sharing (Cont.)
Figure Efficiency data current sharing mode.
Efficiency Current VIN(MASTER) VIN(SLAVE) VOUT 2.75V
Current Sharing Evaluation Board intended specific application. power components optimized minimum cost size. This evaluation board should used understand operation SC1175. design with SC1175 specific current sharing applications. Please refer Application note AN00-3.
2000 Semtech Corp.
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SC1175
POWER MANAGEMENT Evaluation Board Schematic Channel with Current Sharing
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SC1175
POWER MANAGEMENT Evaluation Board Bill Materials Channels with Current Sharing
Item Quantity 15,C 10,C 11,C 12,C 13,C 17,C 18,C M1,M3 M2,M4 R2,R3,R4,R5,R6,R7,R8 R9,R10 eference .22uF, 1uF, 10nF, 1nF, 100uF, 150uF, L4148 7.5uH, 4.7uH, IRF7809 B7030 IRF7811 B7030 Part
.006
.003
1175
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SC1175
POWER MANAGEMENT Evaluation Board Gerber Plots Channels with Current Sharing
Side Traces
Bottom Side Traces
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SC1175
POWER MANAGEMENT Typical Characteristics Independent Channels
Figure
Figure Output Current
Input Voltage 5Amps. 2A/DIV.
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SC1175
POWER MANAGEMENT Typical Characteristics Independent Channels (Cont.)
Figure Peak Peak Output Ripple
Input Voltage 12V. Output Voltage 2.0V Figure Phase Node Input (without snubber network.
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SC1175
POWER MANAGEMENT Typical Characteristics Independent Channels (Cont.)
Figure Start-up Power
Chan. Output Current. 2A/DIV. Chan. Bias Voltage Figure Power
Chan. Output Current. 2A/DIV. Chan. Bias Voltage
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SC1175
POWER MANAGEMENT Typical Characteristics Independent Channels Efficiency Test
Figure
EFFICIENCY OUTPUT CURRENT Vout 2.0V 1.25V Vout
Independent Channels Evaluation Board intended specific application. power components optimized minimum cost size. This evaluation board should used understand operation SC1175. design with SC1175 specific independent channels applications. Please refer Application note AN00-4.
2000 Semtech Corp.
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SC1175
POWER MANAGEMENT Evaluation Board Schematic Independent Channels
2000 Semtech Corp.
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SC1175
POWER MANAGEMENT Evaluation Board Bill Materials Independent Channels
Item Quantity 12,C 13,C 14,C 15,C 16,C 17,C 18,C 19,C 21,C 22,C M1,M3 M2,M4 R1,R2,R3,R4,R5,R6,R7 R8,R9,R13 R14,R15 eference 1uF, .22uF, 1nF, 10nF, 150uF, 100uF, L4148 7.5uH, 4.7uH, IRF7809 B7030 IRF7811 B7030 .006 .003 1175 Part
2000 Semtech Corp.
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SC1175
POWER MANAGEMENT Evaluation Board Gerber Plots Independent Channels
Side Traces
Bottom Side Traces
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SC1175
POWER MANAGEMENT Layout
Power signal traces must kept separated noise considerations. Feedback, current sense traces analog ground should cross traces planes carrying high switching currents, such input loop phase node. input loop, consisting input capacitors both MOSFETs must kept small possible. high switching currents occur this loop. enclosed loop area must kept small minimize inductance radiated conducted emissions. Designing minimum trace length always best approach, often more optimum layout achieved keeping loop area constraints mind. important keep gate lengths short, must close power switches. This more difficult dual channel device than single requires that power paths either side centrally located controller. Grounding requirements always conflicting buck converter, especially high power, trick achieve best compromise. Power ground (PGND) should returned bottom MOSFET source provide best gate current return path. Analog ground (GND) should returned ground side output capacitors that analog circuitry controller electrically quiet reference provide greatest feedback accuracy. problem that differential voltage capability grounds limited about proper operation physical separation between grounds must also minimized. grounds apart, fast current transitions connection generate voltage spikes exceeding capability, resulting unstable erratic behavior. feedback divider must close returned analog ground. Current sense traces must parallel close each other analog ground. must have ceramic decoupling capacitor across supply pins, mounted close device possible. small ceramic, noise-filtering capacitors current sense lines should also placed close possible.
Outline Drawing SO-20
Contact Information
Contact Information
Ref. MS-013AC
ECN00-1204
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Semtech Corporation Power Management Products Division Mitchell Rd., Newbury Park, 91320 Phone: (805)498-2111 (805)498-3804
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