SC4611 high performance synchronous buck controller that configured wi

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SC4611 high performance synchronous buck controller that configured wi

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Wide Input Range High Performance Synchronous Buck Switching Regulator
SC4611 high performance synchronous buck controller that configured wide range applications. SC4611 utilizes synchronous rectified buck topologies where high efficiency primary consideration. optimized applications involving multiple redundant convertors connected together. star asynchronous, which keeps lower side during soft start. This desired feature when convertor turned with preset external voltage pre-bias voltage already present across output. With lower off, external discharged which avoids latch-up modern ASIC circuits. SC4611 comes with rich features like regulated supply, soft start, power-good signaling, high current gate drivers, bootstrapped supply driving high side Nchannel MOSFETs, shoot through protection, frequency synchronization option overvoltage crowbar. also features multi mode overload protection that includes continuous current limiting, hiccup mode followed latch off. user option bypassing hiccup mode latch output required.
SC4611
Features
Wide input range, Output voltage 0.5V output drive capability Asynchronous start mode Multimode overcurrent protection with current limit, hiccup mode latched shutdown Overvoltage crowbar protection Power signal Programmable frequency with external synchronization degree operating temperature Thermal shutdown Small package TSSOP-20
Applications
Distributed power architectures Telecommunication equipment Servers/work stations Mixed signal applications Paralleled synchronous buck convertors Base station power management
Typical Application Circuit
(30V MAX)
Lout
VOUT (0.5V MIN)
Cout
SC4611
CSOVP PGND
Rclset
Revision: November 2004
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SC4611
POWER MANAGEMENT Absolute Maximum Ratings
Exceeding specifications below result permanent damage device, device malfunction. Operation outside parameters specified Electrical Characteristics section implied. Exposure Absolute Maximum rated conditions extended periods time affect device reliability.
Parameter PGND PGND PVCC, AVCC PGND PGND AGND PGND Other Pins AGND GDH, Source Sink Current Storage Temperature Range Junction Temperature Lead Temperature (Soldering) Sec.
Symbol VBSTMAX VINMAX AVCCMAX
Maximum ±0.3 -0.3
Units
VGDHMAX, VGDLMAX
PVCC +0.3 AVCC +0.3
IGDHMAX, IGDLMAX TSTGMAX TJMAX
+150 +125
Electrical Characteristics
Unless specified: +85°C, 12V, PVCC AVCC kHz, SS/SH
Parameter Power Supply AVCC PVCC Operating Current Quiescent Current Undervoltage Lockout Start Threshold UVLO Hysteresis Soft Start/Shut Down Charge Current Discharge Current Disable Threshold Voltage Disable Shut
2004 Semtech Corp.
Symbol
Test Conditions
Unit
AVCC PVCC ISUPPLY IQUI
5.5V 5.5V load pins SS/SH
VUVLO
AVCC Rising
0.16
ISSC ISSD
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SC4611
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: +85°C, 12V, PVCC AVCC kHz, SS/SH
Parameter Oscillator Frequency Range Frequency Peak Peak Ramp Voltage(1) Input High Pulse Width Rise/Fall Time Frequency Range High/Low Threshold Error Amplifier Feedback Voltage Input Bias Current
Symbol
Test Conditions
Unit
VRAMP TSYNC
1000
VSYNC +15%
0.493
0.507
Unity Gain Bandwidth Open Loop Gain Output Source/Sink Current Current Sense Comparator offset current (ILIM ADJ) Current limit sense threshold Current limit hysteresis Power Good Overvoltage Protection Level Output High Sense Hysteresis Level Output Sense Hysteresis Output Level Trip Reference VPOK VOVP IPOK 0.475 VHTH 0.42 VLTH 0.52 ICSVCL Rclset IEAO
0.55 0.45
0.58
0.48
0.525
Guaranteed design. tested production.
2004 Semtech Corp. www.semtech.com
SC4611
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: +85°C, 12V, PVCC AVCC kHz, SS/SH
Parameter Duty Cycle Maximum Duty Cycle
Symbol
Test Conditions
Units
Dmax
Minimum Pulse Width Output Gate Drive ON-Resistance Gate Drive OFF-Resistance Gate Drive ON-Resistance Gate Drive OFF-Resistance Rise Time Fall Time Dead Time Between Drive Signals
Tpulsemin
RONGDH ROFFGDH RONGDL ROFFGDL Trise Tfall
ISOURCE ISINK ISOURCE ISINK COUT 2000 COUT 2000
NOTES: Guaranteed design. tested production. This device sensitive. standard handling precautions required
Configuration
VIEW
CSCS+ PVCC PGND AVCC SYNC AGND SS/SH
Ordering Information
Part Number SC4611ITSTRT
ackag TSSOP-20
Temp. Range -40°C +85°C
Notes: Only available tape reel packaging. reel contains 2500 devices. Lead free device. This product fully WEEE RoHS compliant.
TSSOP)
2004 Semtech Corp. www.semtech.com
SC4611
POWER MANAGEMENT Descriptions
Name SS/SH AGND SYNC AVCC PGND Function Switching junction high side Mosfet source side Mosfet drain. Gate drive output high side N-Channel MOSFET. Boost capacitor connection high side gate drive. Connect external capacitor diode shown Typical Application Circuit. Input supply voltage. Base drive AVCC/PVCC regulator. Inverting input current sense comparator inverting input current sense comparator Feedback input pin.The reference level 0.5V Error amplifier output compensation. Open drain power good output. Overvoltage protection input. reference level 0.5V Current Limit Mode select input. Connect AVCC enable hiccup connect AGND bypass hiccup mode. Connect resistor AGND programming oscillator frequency. Soft start pin. Hold shutdown device. Analog signal ground. Oscillator synchronization pin. Connect AGND used. Supply voltage analog circuitry. Power ground. Gate drive output side N-Channel MOSFET. Supply voltage output drivers.
2004 Semtech Corp.
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SYNC
RAMP
SYNC
SYNC
2004 Semtech Corp.
BANDGAP 0.55V UVLO
MONITOR
POWER MANAGEMENT Block Diagram SC4611
AVCC
0.45V AVCC
SHDN
MONITOR
SHDN ILIM
PVCC SS-SEQ ILIM COMP
ENABLE LATCH_1
OUTL OUTH
ILIM CSBST DRIVER PVCC DRIVER
LOGIC LATCH_2
AGND
0.5V
COMP
COMP
PGND
0.5V
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SC4611
SC4611
POWER MANAGEMENT Applications Information
INTRODUCTION INTRODUCTION SC4611 designed control drive N-Channel MOSFET synchronous rectified buck convertors. switching frequency programmable optimize design. SC4611 switching regulator section features external current sensing provides hiccup mode overcurrent protection followed latched shutdown. also optimized multiple convertors operating parallel redundant mode. POWERING CONTROLLER POWERING CONTROLLER Supplies VIN, PVCC AVCC from input source used power SC4611. supply provides bias internal reference UVLO circuitry. AVCC supply provides bias oscillator, switcher, voltage feedback, current sense Power circuitry. PVCC used drive high side MOSFET gates. external transistor linear regulator generate well regulated AVCC PVCC shown Typical Application Circuit. maximum current into should limited under conditions. example external transistor used with less than will saturate pull down input. series resistor between base external transistor should used limit current into pin. pins have absolute maximum rating maximum less than connected directly AVCC PVCC, leaving open. START SEQUENCE Start inhibited until AVCC input reaches UVLO threshold. UVLO limit 4.2V typical. power sequence initiated current source charging soft start capacitor connected pin. When reaches converter will start switching. reference input error amplifier ramped with soft-start signal, level shifted down Initially only high side driver enabled. Keeping side MOSFET during start useful where multiple convertors operating parallel. prevents forward conduction freewheeling MOSFET which might otherwise cause common output bus.
2004 Semtech Corp.
When reaches side MOSFET will begin switch convertor fully operational synchronous mode. reference input error amplifier released pulled AVCC. soft start duration controlled value cap. pulled below 0.5V, device disabled draws only current. Note that threshold soft-start supply dependant defined above AVCC AVCC lower, threshold should reduced proportionately, i.e. enable threshold will 0.375V when AVCC 4.5V. GATE DRIVERS side gate driver supplied from PVCC provides peak source/sink current high side gate drive also capable sourcing sinking peak currents Protection logic provides dead time ensure both upper lower MOSFETs will turn simultaneously cause shoot through condition. high side MOSFET gate drive provided external supply that connected from GND. actual gate source voltage upper MOSFET will approximately equal (12V-VCC). external supply available, classical bootstrap technique implemented from PVCC supply. bootstrap capacitor connected from Phase while PVCC connected through diode (Low Schottky ultrafast diode) BST. This will provide gate source voltage approximately equal VCC-Vdiode drop. OSCILLAT OSCILLATOR switching frequency SC4611 external resistor using following formula:
9375
kOhm kHz. This relation first order approximation more complex relationship between Fsw. oscillator synchronised external clock that nominally faster than internal frequency ROSC. external voltage level applied should lower than AVCC device.
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SC4611
POWER MANAGEMENT Applications Information (Cont.)
OVERCURRENT PROTECTION VERCURRENT SC4611 includes precision current sense comparator maximum flexibility. current feedback taken either from output inductor lossless sensing better efficiency, from series resistor improved accuracy. offset current 1.225/RT pulls CSpin, providing offset voltage across resistance input this pin. offset voltage should voltage across current sense resistor greater than this value will produce current limit pulse. There hysteresis offset current. Since offset current into current limit needs adjusted frequency setting changed. Note that operational limit inputs 0.5V below AVCC supply. first stage protection against overloads peak current limiting pulse pulse basis. Once overload sensed, high side turned held rest cycle. This provides peak current limiting pulse pulse basis. final response device severe overload programmed using pin. connected AVCC, hiccup mode enabled. soft-start/hiccup cycle initiated current limit pulses detected counting period oscillator cycles. capacitor discharged with sink current. There will dummy soft-starts, i.e. will pulled then discharged This will repeated times, overload persists part will latched eighth attempt. Reset recycling input power. During hiccups, device will operate asynchronous mode, just powerup sequence. some cases repeated soft start cycling desirable, depending nature load. taken AGND, hiccup mode will skipped. When overcurrent event occurs comparator detects puts signal into latch counter. counter keeps track number current-limit pulses reset after every oscillator cycles. current-limit pulses detected counting period cycles, will pulled low. device latched until power recycled. should connected either AGND AVCC times should left open. POWER MONITOR POWER MONITOR power circuitry monitors input error amplifier. voltage this input goes above 0.55V below 0.45V pulled low. open drain output held until startup sequence i.e. till reaches more. VERVOLT OVERVOLTAGE THERMAL PROTECTION overvoltage input connected with reference 0.5V. this feedback exceeds reference side continuously gated crowbar input VIN. This feature used protect load from possible overvoltage case high side fails shorts. crowbar current power devices limited only source VIN. SC4611 also incorporates thermal protection. chip temperature exceeds approximately outputs shutdown. ERROR ERROR AMPLIFIER DESIGN SC4611 voltage mode buck controller that utilizes externally compensated high bandwidth error amplifier regulate output voltage. power stage synchronous rectified buck converter control-to-output transfer function shown below:
sESRCC
where, Input voltage Output inductance ESRC Output capacitor Peak peak ramp voltage Load resistance Output capacitance
2004 Semtech Corp.
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SC4611
POWER MANAGEMENT Applications Information (Cont.)
classical Type compensation network built around error amplifier shown below
Vref
design guidelines following: loop gain crossover frequency given switching frequency. Place integrator origin increase frequency gains. Select such that they placed near dampen peaking; loop gain rate across line obtaining wide bandwidth. Cancel wESR with compensation pole (wP1 wESR Place high frequency compensation pole half switching frequency maximum attenuation switching ripple high frequency noise with adequate phase SC461 LAYOUT SC4611 Careful attention layout requirements necessary successful implementation SC4611 controller. High switching currents with fast rise fall times present application their effect ground plane voltage differentials must understood minimized. good layout with minimum parasitic loop areas will
Figure Voltage Mode Buck Converter Compensation Network transfer function compensation network follows:
where,
GCOMP
R2C1
R1(C1
R3C2
reduce lower ground injection currents, resulting electrically "cleaner" grounds rest system minimize source ringing, resulting more reliable gate switching signals. LAYOUT GUIDELINES
Loop gain T(s)
following denote high side side MOSFETs respectively. ground plane should used. number position ground plane interruptions should minimised compromise ground plane integrity. Isolated semiisolated areas ground plane deliberately introduced constrain ground currents into particular paths, such output capacitor source.
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Figure Simplified asymptotic diagram buck power stage compensated loop gain.
2004 Semtech Corp.
SC4611
POWER MANAGEMENT Applications Information (Cont.)
high power, high current parts circuit should laid first. time loop formed input capacitor Cin, high side output inductor output capacitor bank Cout must kept small possible. Another loop area minimise formed side output inductor output capacitor bank Cout during period. These loops contain high current, fast transition switching. Connections should wide short possible minimize loop inductance. connection between junction output inductor should wide trace copper region. should short practical. Since this connection fast voltage transitions, keeping this connection short will minimize EMI. Also keep Phase connection short. gate charge currents flow this trace. output capacitor Cout should located close load terminals possible. Fast transient load currents supplied Cout connections between Cout load must kept short with wide copper areas minimize inductance resistance. This will improve transient response step loads. SC4611 best placed over quiet ground plane area. Avoid pulse currents Cin, loop flowing this area. This analog ground plane should connected power ground plane "quiet" point near input capacitor. Under circumstance should returned point inside Cin, Cout power ground loops. SC4611 AGND connected separate analog ground plane with minimum lead length analog grounding paths including decoupling capacitors, feedback resistors, compensation components, current-limit setting resistors should connected same plane.
3.3V/10A Evaluation Board Schematic
SHORT
3.3V
10-15V 3.3V/10A Reference Design With SC4611
6612 TP14 6670 6670 TP15 .01R/1W .01R/1W VOUT
3906 J6-3
VOUT
AVCC PVCC 30.1K
J5-1
1.62K
1.62K
J5-3
SYNC 4148 TP12 TP13 33.2K TP11 1.78K 249R
PGND
J6-4
SC4611ITSTR
J5-2
J6-1
J6-2
J5-4
2004 Semtech Corp.
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SC4611
POWER MANAGEMENT Outline Drawing TSSOP-20
INDICATOR TIPS
DIMENSIONS INCHES MILLIMETERS
.047 .006 .002 .042 .031 .007 .012 .007 .003 .251 .255 .259 .169 .173 .177 .252 .026 .018 .024 .030 (.039) .004 .004 .008 1.20 0.05 0.15 0.80 1.05 0.19 0.30 0.20 0.09 6.40 6.50 6.60 4.30 4.40 4.50 6.40 0.65 0.45 0.60 0.75 (1.0) 0.10 0.10 0.20
SEATING PLANE
GAGE PLANE 0.25
(L1) DETAIL
SIDE VIEW
NOTES:
DETAIL
CONTROLLING DIMENSIONS MILLIMETERS (ANGLES DEGREES). -HTO DETERMINED DATUM PLANE
DATUMS
DIMENSIONS "E1" INCLUDE MOLD FLASH, PROTRUSIONS GATE BURRS. REFERENCE JEDEC MO-153, VARIATION
Land Pattern TSSOP-20
DIMENSIONS INCHES MILLIMETERS
(.222) .161 .026 .016 .061 .283 (5.65) 4.10 0.65 0.40 1.55 7.20
NOTES:
THIS LAND PATTERN REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES MET.
Contact Information
Semtech Corporation Power Management Products Division Flynn Road, Camarillo, 93012 Phone: (805)498-2111 (805)498-3804
2004 Semtech Corp. www.semtech.com

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