MIC2193 400kHz SO-8 Synchronous Buck Control General Descrip
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MIC2193
MIC2193
400kHz SO-8 Synchronous Buck Control
General Description
Micrel's MIC2193 high efficiency, synchronous buck control housed SO-8 package. 2.9V input voltage range allows efficiently step down voltages 3.3V, systems well 2-cell battery powered applications. MIC2193 solution saves valuable board space. device housed space-saving SO-8 package, whose pin-count minimizes external components. 400kHz operation allows small inductor small output capacitors used. MIC2193 implement allceramic capacitor solutions. MIC2193 drives high-side P-channel MOSFET, eliminating need high-side boot-strap circuitry. This feature allows MIC2193 achieve maximum duty cycles 100%, which useful headroom applications. output driver impedance allows MIC2193 drive large external MOSFETs generate wide range output currents. MIC2193 available SOIC package with junction temperature range -40°C +125°C.
Features
2.9V input voltage range 400kHz oscillator frequency current mode control 100% maximum duty cycle Front edge blanking output drivers Cycle-by-cycle current limiting Frequency foldback short circuit protection lead SOIC package Point load power supplies Distributed power systems Wireless Modems ADSL line cards Servers Step down conversion 3.3V, systems 1-and 2-cell battery operated equipment
Applications
Typical Application
3.3V 120µF 6.3V 2.2nF
0.012 MIC2193BM OUTP Si9803 3.8µH Si9804 22.6k
VOUT 1.8V, 220µF 6.3V
COMP OUTN
Adjustable Output Synchronous Buck Converter
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 474-1000 http://www.micrel.com
April 2004
M9999-042704
MIC2193
Ordering Information
Part Number MIC2193BM MIC2193YM Voltage Adjustable Adjustable Frequency 400KHz 400KHz Temperature Range -40°C +125°C -40°C +125°C Package 8-lead 8-lead Lead Finish Standard Pb-Free
Configuration
COMP OUTP OUTN
Lead SOIC
Description
Number Name COMP Function Controller supply voltage. Also input current sense amp. Compensation (Output): Internal error amplifier output. Connect capacitor series network compensate regulator's control loop. Feedback Input: circuit regulates this 1.245V. input current limit comparator. built offset 110mV between conjunction with current sense resistor sets current limit threshold level. This also input current amplifier. internal linear-regulator output. also supply voltage chip. Bypass with 1µF. Ground. High current drive synchronous N-channel MOSFET. Voltage swing from ground VIN. On-resistance typically 5VIN. High current drive high side P-channel MOSFET. Voltage swing from ground VIN. On-resistance typically 5VIN.
OUTN OUTP
M9999-042704
April 2004
MIC2193
Absolute Maximum Ratings (Note
Supply Voltage (VIN) Digital Supply Voltage (VDD) Comp Voltage (VCOMP) -0.3V Feedback Voltage (VFB) -0.3V Current Sense Voltage (VIN VCS) -0.3V Power Dissipation (PD) 285mW 85°C Ambient Storage Temp -65°C +150°C Rating Note
Operating Ratings (Note
Supply Voltage (VIN) +2.9V +14V Junction Temperature -40°C +125°C Package Thermal Resistance 8-lead 140°C/W
Electrical Characteristics
VOUT 3.3V, 25°C, unless otherwise specified. Bold values indicate -40°C<TJ<+125°C. Parameter Regulation Feedback Voltage Reference Feedback Bias Current Output Voltage Line Regulation Output Voltage Load Regulation Output Voltage Total Regulation Input Supply Input Current (IQ) Digital Supply Voltage (VDD) Digital Supply Load Regulation Undervoltage Lockout UVLO Hysteresis Current Limit Current Limit Threshold Voltage Error Amplifier Error Amplifier Gain Current Amplifier Current Amplifier Gain Oscillator Section Oscillator Frequency (fO) Maximum Duty Cycle Minimum Time Frequency Foldback Threshold Frequency Foldback Frequency 1.0V 1.5V Measured voltage trip current limit (excluding external MOSFET gate current) upper threshold (turn threshold) 2.82 2.65 3.18 (VIN VCS) 75mV 12V, (VIN VCS) 75mV (±3%) 1.208 (1%) (2%) 1.233 1.22 1.245 1.245 0.09 1.282 1.257 1.27 Condition Units
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MIC2193
Parameter Gate Drivers Rise/Fall Time Output Driver Impedance 3300pF Source, Sink, Source, Sink, 3.3V Condition
Units
Driver Non-overlap Time
Note
Absolute maximum ratings indicate limits beyond which damage component occur. Electrical specifications apply when operating device outside operating ratings. maximum allowable power dissipation function maximum junction temperature, TJ(Max), junction-to-ambient thermal resistance, ambient temperature, device guaranteed function outside operating rating. Devices sensitive, handling precautions required. Human body model, 1.5k series with 100pF.
Note Note
M9999-042704
April 2004
MIC2193
Typical Characteristics
Quiescent Current Supply Voltage
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
Quiescent Current Temperature
3.15 3.10 3.05 3.00 2.95 2.90 2.85 2.80
Input Voltage
SUPPLY VOLTAGE
TEMPERATURE (°C)
INPUT VOLTAGE
3.06 3.04 3.02 3.00 2.98 2.96 2.94 2.92 2.90
3.30 3.20 3.10 3.00 2.90 2.80 2.70 2.60
REFERENCE VOLTAGE
3.10 3.08
Load
3.50 3.40
Temperature
Reference Voltage Temperature
1.300 1.290 1.280 1.270 1.260 1.250 1.240 1.230 1.220 1.210 1.200 TEMPERATURE (°C)
3.3V
LOAD CURRENT (mA)
2.50 TEMPERATURE (°C)
CURRENT LIMIT THRESHOLD (mV)
Switching Frequency Input Voltage
FREQUENCY VARIATION
Switching Frequency Temperature
Overcurrent Threshold Input Voltage
INPUT VOLTAGE
FREQUENCY VARIATION
-0.5 -1.0 -1.5 -2.0 INPUT VOLTAGE
TEMPERATURE (°C)
Current Limit Threshold Temperature
CURRENT LIMIT THREHOLD (mV)
TEMPERATURE (°C) IMPEDANCE 14.0 12.0 10.0
OUTN Drive Impedance Input Voltage
IMPEDANCE
OUTN Drive Impedance Input Voltage
Sink
Source
Source Sink INPUT VOLTAGE INPUT VOLTAGE
April 2004
M9999-042704
MIC2193
Functional Diagram
CDECOUP
OVERCURRENT COMPARATOR
VREF 1.245V
RSENSE BIAS
GAIN
CURRENT SENSE
fs/4 CONTROL
OUTP VOUT
OUTN
COUT
RESET SLOPE COMPENSATION
COMPARATOR 0.0002 VREF gain COMP
ERROR 100k
0.3V fs/4
FREQUENCY FOLDBACK
Figure MIC2193 Block Diagram
Functional Characteristics
Controller Overview Functional Description MIC2193 BiCMOS, switched mode, synchronous step down (buck) converter controller. uses both Pchannel MOSFETs, which allows controller operate 100% duty cycle eliminates need high-side drive boot-strap circuit. Current mode control used achieve superior transient line load regulation. internal corrective ramp provides slope compensation stable operation above duty cycle. controller optimized high efficiency, high performance DC-DC converter applications. Figure block diagram MIC2193 configured synchronous buck converter. beginning switch6
cycle, OUTP pulls turns high-side P-Channel MOSFET, Current flows from input output through current sense resistor, MOSFET, inductor. current amplitude increases, controlled inductor. voltage developed across current sense resistor, RSENSE, amplified inside MIC2193 combined with internal ramp stability. This signal compared output error amplifier. When current signal equals error voltage signal, P-channel MOSFET turned off. inductor current flows through diode, until synchronous, N-channel MOSFET turns voltage drop across MOSFET less than forward voltage drop diode, which improves converter efficiency. switching period, synchronous MOSFET turned switching cycle repeats. April 2004
M9999-042704
MIC2193
MIC2193 controller broken down into five functions. Control loop operation Current mode control Current limit Reference MOSFET gate drive Oscillator Control Loop
Control Loop
Current Limit output current detected voltage drop across external current sense resistor (RSENSE Figure 1.). current sense resistor must sized using minimum current limit threshold. external components must designed withstand maximum current limit. current sense resistor value calculated equation below:
RSENSE CURRENT SENSE THRESHOLD IOUT
MIC2193 uses current mode control regulate output voltage. This dual control loop method (illustrated Figure senses output voltage (outer loop) inductor current (inner loop). uses inductor current output voltage determine duty cycle buck converter. Sampling inductor current effectively removes inductor from control loop, which simplifies compensation.
Switching Converter VOUT
maximum output current
IOUT CURRENT SENSE THRESHOLD RSENSE
Voltage Divider IINDUCTOR Switch Driver VERROR VREF
IINDUCTOR
current sense pins (pin (pin noise sensitive signal level high input impedance switching noise pin. traces should short routed close each other. 10nF capacitor across pins will attenuate high frequency switching noise. When peak inductor current exceeds current limit threshold, overcurrent comparator turns high side MOSFET remainder switching cycle, effectively decreasing duty cycle. output voltage drops additional load current pulled from converter. When voltage feedback (FB) reaches approximately 0.3V, circuit enters frequency foldback mode oscillator frequency will drop approximately switching frequency. This limits maximum output power delivered load under short circuit condition. Reference Circuits output drivers enabled when voltage (pin greater than undervoltage threshold. internal bias circuit generates internal 1.245V bandgap reference voltage voltage error amplifier voltage internal control circuitry. must decoupled with ceramic capacitor. capacitor must placed close pin. other capacitor must connected directly ground plane. MOSFET Gate Drive MIC2193 designed drive high-side, P-Channel MOSFET side, N-Channel MOSFET. source P-channel MOSFET connected input power supply. turned when OUTP pulls gate MOSFET low. advantage using P-channel MOSFET that does required bootstrap circuit boost gate voltage higher than input, would required Nchannel MOSFET. (pin supplies drive voltage both gate drive pins, OUTN OUTP. must well decoupled prevent noise from affecting current sense circuit, which uses sense pins. non-overlap time built into MOSFET driver circuitry. This dead time prevents high-side low-side MOSFET drivers from being same time. Either external diode low-side MOSFET internal parasitic diode conducts inductor current during dead time.
VERROR
tPER tON/tPER
Figure Current Mode Control Example shown Figure inductor current sensed measuring voltage across resistor, RSENSE. ramp added amplified current sense signal provide slope compensation, which required prevent unstable operation duty cycles greater than 50%. transconductance amplifier used error amplifier, which compares attenuated sample output voltage with reference voltage. output error amplifier compensation (COMP), which compared current sense waveform block. When current signal becomes greater than error signal, comparator turns high-side drive. COMP provides access output error amplifier allows external components stabilize voltage loop.
April 2004
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MIC2193
MOSFET Selection P-channel MOSFET must have threshold voltage equal lower than input voltage when used buck converter topology. There limit maximum gate charge MIC2193 will drive. MOSFETs with higher gate charge will have slower turn-on turn-off times. Slower transition times will cause higher power dissipation MOSFETs higher switching transition losses. MOSFETs must able completely turn within driver non-overlap time both MOSFETs conducting same time, shoot-through will occur, which greatly increases power dissipation MOSFETs reduces converter efficiency. MOSFET gate charge also limited power dissipation MIC2193. power dissipated gate drive circuitry calculated below: PGATE_DRIVE QGATE where: QGATE total gate charge both Pchannel MOSFETs. switching frequency gate drive voltage graph Figure shows total gate charge that driven MIC2193 over input voltage range, different values switching frequency.
Max. Gate Charge
MAXIMUM GATE CHARGE (nC)
INPUT VOLTAGE
MIC2193 Voltage Amplifier VREF 1.245V VOUT
Figure output voltage determined equation below. Where: VREF MIC2193 typically 1.245V. Lower values preferred prevent noise from appearing pin. typically recommended value 10k. small value will decrease efficiency power supply, especially output loads. Once selected, calculated with following formula. VOUT VREF VREF VOUT VREF
Figure MIC2193 Frequency Max. Gate Charge Oscillator internal oscillator free running requires external components. maximum duty cycle 100%. This another advantage using P-channel MOSFET high-side drive: continuously turned frequency foldback mode enabled voltage feedback (pin less than 0.3V. frequency foldback, oscillator frequency reduced approximately factor Frequency foldback used limit energy delivered output during short circuit fault condition. Voltage Setting Components MIC2193 requires resistors output voltage shown Figure
Efficiency Considerations Efficiency ratio output power input power. difference dissipated heat buck converter. Under light output load, significant contributors are: supply current maximize efficiency light loads: gate charge MOSFET smallest MOSFET, which still adequate maximum output current. ferrite material inductor core, which less core loss than iron power core. Under heavy output loads significant contributors power loss approximate order magnitude): Resistive time losses MOSFETs Switching transition losses high side MOSFET Inductor resistive losses Current sense resistor losses Input capacitor resistive losses (due capacitors ESR) minimize power loss under heavy loads: resistance MOSFETs. threshold logic level MOSFETs when input voltage below Multiplying gate charge resistance gives figure merit, providing good balance between load high load efficiency. Slow transition times oscillations voltage current waveforms dissipate more power during turn turn MOSFETs. clean layout will minimize parasitic inductance capacitance gate drive high current paths. This will allow fastest transition times waveforms without oscillations. gate charge MOSFETs will April 2004
M9999-042704
MIC2193
transition faster than those with higher gate charge requirements. same size inductor, lower value will have fewer turns therefore, lower winding resistance. However, using small value will require more output capacitors filter output ripple, which will force smaller bandwidth, slower transient response possible instability under certain conditions. Lowering current sense resistor value will crease power dissipated resistor. However, will also increase overcurrent limit will require larger MOSFETs inductor components. input capacitors minimize power dissipated capacitors ESR.
April 2004
M9999-042704
MIC2193
Package Information
0.026 (0.65) MAX)
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.050 (1.27)
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102) 0°-8° SEATING PLANE 0.010 (0.25) 0.007 (0.18)
0.064 (1.63) 0.045 (1.14)
0.197 (5.0) 0.189 (4.8)
0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
8-Pin SOIC
MICREL, INC. 1849 FORTUNE DRIVE JOSE, 95131
(408) 944-0800
(408) 474-1000
http://www.micrel.com
information furnished Micrel this data sheet believed accurate reliable. However, responsibility assumed Micrel use. Micrel reserves right change circuitry specifications time without notification customer. Micrel Products designed authorized components life support appliances, devices systems where malfunction product reasonably expected result personal injury. Life support devices systems devices systems that intended surgical implant into body support sustain life, whose failure perform reasonably expected result significant injury user. Purchaser's sale Micrel Products life support appliances, devices systems Purchaser's risk Purchaser agrees fully indemnify Micrel damages resulting from such sale. 2004 Micrel, Incorporated. M9999-042704
April 2004
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