MIC2194 400kHz SO-8 Buck Control Final Information General D
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MIC2194
MIC2194
400kHz SO-8 Buck Control Final Information
General Description
Micrel's MIC2194 high efficiency 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. flexible architecture MIC2194 allows configured buck buck-boost converter. MIC2194 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. MIC2194 implement allceramic capacitor solutions. MIC2194 drives high-side P-channel MOSFET. output driver impedance allows MIC2194 drive large external MOSFETs generate wide range output currents. MIC2194 achieve maximum duty cycles 100%, which useful headroom applications. MIC2194 available SOIC package with junction temperature range -40°C +125°C.
Features
2.9V input voltage range 400kHz oscillator frequency current mode control output drivers 100% maximum duty cycle 0.5µA micro-power shutdown Programmable UVLO Front edge blanking Cycle-by-cycle current limiting Frequency foldback short circuit protection 8-lead SOIC package Point load power supplies Negative voltage buck-boost power supplies Distributed power systems Base stations Wireless modems ADSL line cards Servers Step down conversion 3.3V, systems 1-and 2-cell battery operated equipment
Applications
Typical Application
47µF 0.012 MIC2194BM OUTP UVLO 2.2nF COMP 3.32k Si4431A 5.2µH B530 220µF
VOUT
Adjustable Output Buck Converter
+3.3V 10µF 0.040 MIC2194BM OUTP UVLO 4.99k COMP 10nF VOUT -5V, 0.6A B530 3.01k 22nF 220µF Si9803 22µH
10µF
Positive-to-Negative Buck-Boost Converter
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
March 2002
MIC2194
MIC2194
Ordering Information
Part Number MIC2194BM Output Voltage Adjustable Frequency 400KHz Junction Temp. Range -40°C +125°C Package 8-lead
Configuration
COMP EN/UVLO OUTP
Lead SOIC
Description
Number Name COMP EN/UVLO Function Compensation (Output): Internal error amplifier output. Connect capacitor series network compensate regulator's control loop. Feedback (Input): circuit regulates this 1.245V. Enable/Undervoltage Lockout (input): level this will power down device, reducing quiescent current under 0.5µA. This separate thresholds, below 1.5V output switching disabled, below 0.9V device forced into complete micropower shutdown. 1.5V threshold functions accurate undervoltage lockout (UVLO) with hysteresis. input current limit comparator. built-in 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. Input voltage circuit. Also high side input current sense amplifier supplies power gate drive circuit.
OUTP
MIC2194
March 2002
MIC2194
Absolute Maximum Ratings (Note
Supply Voltage (VIN) Digital Supply Voltage (VDD) Enable Voltage (VEN) -0.3V +15V 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) Shutdown Current (ISD) Digital Supply Voltage (VDD) Digital Supply Load Regulation Undervoltage Lockout UVLO Hysteresis Enable/UVLO Enable Input Threshold UVLO Threshold Enable Input Current 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 VEN/UVLO (excluding external MOSFET gate current) upper threshold (turn threshold) 2.82 2.65 3.18 (VIN VCS) 75mV (VIN VCS) 75mV (±3%) 1.208 (1%) (2%) 1.233 1.22 1.245 1.245 0.15 1.282 1.257 1.27 Condition Units
March 2002
MIC2194
MIC2194
Parameter Gate Drivers Rise/Fall Time Output Driver Impedance 3300pF Source, Sink, Source, Sink, Condition
Units
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
MIC2194
March 2002
MIC2194
Typical Characteristics
Quiescent Current Input Voltage
QUIESCENT CURRENT (mA) QUIESCENT CURRENT (mA) Standby INPUT VOLTAGE Switching TEMPERATURE (°C) 3.00 2.95 2.90 2.85 2.80
Quiescent Current Temperature
3.05
Input Voltage
INPUT VOLTAGE
3.05
Load
3.50 3.40 3.30 3.20 3.10 3.00 2.90 2.80 2.70
Temperature
REFERENCE VOLTAGE
Error Reference Voltage Input Voltage
1.2455 1.2450 1.2445 1.2440 1.2435 1.2430
3.03 3.3V 3.01 2.99 2.97 2.95 2.93 2.91 2.89 2.87 2.85
LOAD CURRENT (mA)
2.60 2.50 TEMPERATURE (°C)
INPUT VOLTAGE
Error Reference Voltage Temperature
FREQUENCY VARIATION REFERENCE VOLTAGE 1.29 1.28 1.27 1.26 1.25 1.24 1.23 1.22 1.21 TEMPERATURE (°C)
Frequency Variation Input Voltage
SOFT START CURRENT (µA)
Frequency Variation Temperature
-0.5 -1.5
INPUT VOLTAGE
TEMPERATURE (°C)
Overcurrent Threshold Input Voltage
CURRENT LIMIT (mV) THRESHOLD (mV) INPUT VOLTAGE
Current Limit Threshold Temperature
IMPEDANCE
OUTP Drive Impedance Input Voltage
Source()
Sink
TEMPERATURE (°C)
INPUT VOLTAGE
March 2002
MIC2194
MIC2194
Functional Diagram
CDECOUP
VREF 1.245V
OVERCURRENT COMPARATOR
0.1V Threshold EN/UVLO
RSENSE
BIAS
GAIN
CURRENT SENSE
fs/4 CONTROL
OUTP VOUT COUT
RESET SLOPE COMPENSATION
COMPARATOR 0.0002 VREF gain COMP
ERROR 100k
0.3V fs/4
FREQUENCY FOLDBACK
Figure MIC2194 Block Diagram
Functional Characteristics
Controller Overview Functional Description MIC2194 BiCMOS, switched-mode, step down (buck) converter controller. uses P-channel MOSFET, which allows controller operate 100% duty cycle eliminates need high side drive bootstrap 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 MIC2194 configured buck converter. beginning switching cycle, MIC2194
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 MIC2194 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, beginning next switching cycle, P-channel MOSFET turned which turns diode,
March 2002
MIC2194
MIC2194 controller broken down into several functions. Control loop operation Current mode control Current limit Reference, enable UVLO 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
maximum output current
IOUT CURRENT SENSE THRESHOLD RSENSE
MIC2194 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
Voltage Divider IINDUCTOR Switch Driver VERROR VREF
IINDUCTOR
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.
current sense pins (pin (pin noise sensitive signal level, high input impedance input ripple voltage. traces should short routed close each other. 0.1µF 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 switching frequency. This limits maximum output power delivered load under short circuit condition. Reference, Enable UVLO Circuits output drivers enabled when following conditions satisfied: voltage (pin greater than undervoltage threshold. voltage enable (pin greater than enable UVLO threshold. enable (pin threshold levels, allowing MIC2194 shut down current mode, turn output switching standby mode. enable voltage lower than shutdown threshold turns internal circuitry places MIC2194 micropower shutdown mode. enable voltage between shutdown standby thresholds, internal bias, reference voltages turned output drivers inhibited from switching. OUTP high state. Raising enable voltage above standby threshold enables output driver. standby threshold specified electrical characteristics. resistor divider used with enable prevent power supply from turning until specified input voltage reached. circuit Figure shows connect resistors.
March 2002
MIC2194
MIC2194
MIC2194 1.5V Typical
MOSFET Selection P-channel MOSFET must have threshold voltage equal lower than input voltage when used buck converter topology. There limit maximum gate charge MIC2194 will drive. MOSFETs with high gate charge will have slower turn-on turn-off times. Slower transition times will cause higher power dissipation MOSFET higher switching transition losses. MOSFET gate charge also limited power dissipation MIC2194. 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 MIC2194 over input voltage range, different values switching frequency.
Gate Charge
MAMIMUM GATE CHARGE (nC)
Bias Circuitry EN/UVLO 140mV Hysteresis (typical)
Figure UVLO Circuitry line voltage turn trip point VINPUT ENABLE VTHRESHOLD
where: VTHRESHOLD voltage level internal comparator reference, typically 1.5V. input voltage hysteresis equal VINPUT HYST VHYST
where: VHYST internal comparator hysteresis level, typically 140mV. VINPUT_HYST hysteresis input voltage MIC2194 will disabled when input voltage drops back down VINPUT_OFF VINPUT_ENABLE VINPUT_HYST (VTHRESHOLD VHYST) Either UVLO conditions will pull soft start capacitor low: When voltage drops below undervoltage lockout level. When enable drops below enable 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 MIC2194 designed drive high-side P-channel MOSFET. source P-channel MOSFET connected input power supply. turned when OUTP pulls gate MOSFET low. advantage using P-channel MOSFET that does require bootstrap circuit boost gate voltage higher than input, would required N-channel MOSFET. (pin supplies drive voltage gate drive pin, OUTP.
INPUT VOLTAGE
Figure MIC2194 Max. Gate Charge Oscillator internal oscillator free running requires external components. maximum duty cycle both frequencies 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 MIC2194 requires resistors output voltage shown Figure
MIC2194
March 2002
MIC2194
MIC2194 Voltage Amplifier VREF 1.245V VOUT
Under heavy output loads significant contributors power loss approximate order magnitude): Resistive time losses MOSFET Switching transition losses MOSFET Inductor resistive losses Current sense resistor losses Input capacitor resistive losses (due capacitors ESR) minimize power loss under heavy loads: on-resistance MOSFETs. threshold logic level MOSFETs when input voltage below Multiplying gate charge on-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 MOSFET. 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 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 decrease power dissipated resistor. However, will also increase overcurrent limit will require larger MOSFETs inductor components. input capacitors minimize power dissipated capacitors ESR.
Figure output voltage determined Where: VREF MIC2194 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
Efficiency Considerations Efficiency ratio output power input power. difference dissipated heat buck converter. Under light output load, significant contributors are: supply current, which includes current required switch external MOSFET. Core losses output inductor. 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.
March 2002
MIC2194
MIC2194
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
MICREL INC. 1849 FORTUNE DRIVE JOSE, 95131
(408) 944-0800
(408) 944-0970
http://www.micrel.com
This information believed accurate reliable, however responsibility assumed Micrel infringement patents other rights third parties resulting from use. license granted implication otherwise under patent patent right Micrel Inc. 2002 Micrel Incorporated
MIC2194
March 2002
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