MIC2183 Voltage Synchronous Buck Control Preliminary Information

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MIC2183 Voltage Synchronous Buck Control Preliminary Information

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MIC2183
MIC2183
Voltage Synchronous Buck Control Preliminary Information
General Description
Micrel's MIC2183 high efficiency synchronous buck control With wide input voltage range 2.9V 14V, MIC2183 used efficiently step voltages down 2-cell battery powered applications, well fixed 3.3V, systems. Efficiencies over achievable over wide range load conditions with MIC2183's control scheme. operating frequency divided raising FREQ/2 VDD. This allows user optimize efficiency versus board space. also allows MIC2183 externally synchronized frequencies below nominal 400KHz. MIC2183 features oscillator output, FreqOut, which used implement simple charge pump voltage applications. output charge pump into gate drive power circuitry VINP pin. This feature allows enhanced gate drive, hence higher efficiencies input voltages. MIC2183 also features shutdown mode, programmable undervoltage lockout, making well-suited portable applications. MIC2183 available 16-pin (small-outline package) with junction temperature range from -40°C +125°C.
Features
Input voltage range: 2.9V >90% efficiency Oscillator frequency 400kHz Frequency divide-by-two Frequency sync 600kHz FreqOut oscillator output allows simple charge pump implementation voltage systems Front edge blanking output drivers (typical) Soft start current mode control shutdown current Cycle-by-cycle current limiting Frequency foldback short circuit protection Adjustable under-voltage lockout 16-pin narrow-body (small outline package) 3.3V 2.5V/1.8V/1.5V conversion power distribution systems Wireless modems ADSL line cards 1-and 2-cell battery operated equipment Satellite Phones
Applications
Typical Application
3.3V
120µF (x2) 6.3V
VINP VINA EN/UVLO FreqOut FREQ/2 COMP SYNC SGND
OUTP
MIC2183 EFFICIENCY
EFFICIENCY
Si9803DY(x2) Si9804DY (x2) 4.7µH B130
MIC2183
OUTN PGND
2.5V
VOUT
220µF (x2) 6.3V
3.3V VOUT 2.5V 200kHz
OUTPUT CURRENT (mA)
Adjustable Output Synchronous Buck Converter
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
August 2001
MIC2183
MIC2183
Ordering Information
Part Number MIC2183BM Output Voltage Adjustable Frequency 200/400KHz Junction Temp. Range -40°C +125°C Package 16-lead
Configuration
VINA FreqOut COMP SGND EN/UVLO VINP FREQ/2 OUTP OUTN PGND SYNC
Lead SOIC
MIC2183
August 2001
MIC2183
Description
Number Name VINA Function Analog voltage input voltage circuit. This powers analog sections does need same voltage (VINP). This provides digital signal output signal half switching frequency. This signal swings from used drive external capacitive doubler provide higher voltage VINP input. Soft start reduces inrush current delays slows output voltage rise time. current source will charge capacitor VDD. capacitor will soft start switching regulator 1.5ms. Compensation (Output): Internal error amplifier output. Connect capacitor series network compensate regulator's control loop. Small signal ground: must routed separately from other grounds terminal COUT. Feedback Input circuit regulates this 1.245V. Enable/UnderVoltage Lockout (input): level this will power down device, reducing quiescent current under 5uA. This separate thresholds, below 1.5V output switching disabled, below 0.9V part forced into complete micropower shutdown. 1.5V threshold functions accurate undervoltage lockout (UVLO) with 140mV hysteresis. input current limit comparator. built offset 100mV between conjunction with current sense resistor sets current limit threshold level. This also input current amplifier. input current limit comparator. built offset 100mV 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 SGND with 1µF. Frequency Synchronization (Input): Connect external clock signal synchronize oscillator. Leading edge signal above 1.5V starts switching cycle. Connect SGND used. MOSFET driver power ground, connects source synchronous MOSFET terminal CIN. High current drive synchronous channel MOSFET. Voltage swing from ground VINP. On-resistance typically High current drive high side channel MOSFET. Voltage swing from ground VINP. On-resistance typically When this low, oscillator frequency 400KHz. When this raised VDD, oscillator frequency 200KHz. Power Input voltage circuit. output gate drivers powered from this supply. current sense resistor should connected close possible this pin.
FreqOut
COMP SGND EN/UVLO
SYNC
PGND OUTN OUTP FREQ/2 VINP
August 2001
MIC2183
MIC2183
Absolute Maximum Ratings (Note
Supply Voltage (VINA, VINP) Digital Supply Voltage (VDD) Comp Voltage (VCOMP) -0.3V Feedback Voltage (VFB) -0.3V Enable Voltage (VEN/UVLO) -0.3V Current Sense Voltage (VCSH-VCSL) -0.3V Sync Voltage (VSYNC) -0.3V Freq/2 Voltage (VFREQ/2) -0.3V Power Dissipation (PD) 400mW 85°C Ambient Storage Temp -65°C +150°C Rating, Note
Operating Ratings (Note
Supply Voltage (VINA, VINP) +2.9V +14V Ambient Operating Temperature -40°C +85°C Junction Temperature -40°C +125°C Output Voltage Range 1.3V PackageThermal Resistance 16-lead 100°C/W
Electrical Characteristics
VINA VINP VCSH VOUT 3.3V, VEN/UVLO VFREQ/2 unless otherwise specified. Bold values indicate Parameter Regulation Feedback Voltage Reference Feedback Bias Current Output Voltage Line Regulation Output Voltage Load Regulation Output Voltage Total Regulation Input Supply VINA Input Current VINP Input Current, Note Shutdown Quiescent Current Digital Supply Voltage (VDD) Digital Supply load regulation Undervoltage Lockout UVLO Hysteresis Enable/UVLO Enable Input Threshold UVLO Threshold UVLO Hysteresis Enable Input Current Soft Start Soft Start Current Current Limit Current Limit Threshold Voltage Error Amplifier Error Amplifier Gain Current Amplifier Current Amplifier Gain Voltage CSH-CSL trip current limit VEN/UVLO (turn-on threshold) (Excluding external MOSFET gate current) VEN/UVLO (IVINA IVINP) upper threshold (turn threshold) 2.82 0.03 2.75 3.18 (VCSH VCSL) 75mV VINA 12V, (VCSH VCSL) 75mV (±3%) 1.208 (±1%) (±2%) 1.233 1.22 0.04 1.282 1.245 1.257 1.27 Condition Units
MIC2183
August 2001
MIC2183
Parameter Oscillator Section Oscillator Frequency (fO) Maximum Duty Cycle Minimum Time Freq/2 Frequency (fO) Frequency Foldback Threshold Frequency Foldback Frequency SYNC Threshold Level SYNC Input Current SYNC Minimum Pulse Width SYNC Capture Range FreqOut Output FreqOut Frequency FreqOut Current Drive Note Sink Source Gate Drivers Rise/Fall Time Output Driver Impedance 3300pF Source; VINP Sink; VINP Source; VINP Sink; VINP Driver Non-Overlap Time VINP VINP
Note
Condiion Units
1.0V 1.5V VFreq/2 Measured
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 recommended. application information I(VINP) VINP. application information limitations maximum operating frequency. frequency FreqOut half frequency oscillator, half frequency external Sync signal.
Note Note Note Note Note
August 2001
MIC2183
MIC2183
Typical Characteristics
Quiescent Current Input Voltage
QUIESCENT CURRENT (mA) ISTANDBY INPUT VOLTAGE 200kHz IVINA IVINP QUIESCENT CURRENT (mA) 400kHz IVINA IVINP VINA VINP 3.3V 400kHz 200kHz ISTANDBY
Quiescent Current Temperature
3.15 3.10 3.05 3.00 2.95 2.90 2.85 2.80
Input Voltage
VINA VINP
100120140 TEMPERATURE (°C)
INPUT VOLTAGE
3.005 3.000 2.995 2.990 2.985 2.980 2.975 2.970
Load
3.04 3.03
Temperature
REFERENCE VOLTAGE
1.246 1.245 1.244 1.243 1.242 1.241 1.240
Error Reference Voltage Temperature
VINA VINP
3.02 3.01 3.00 2.99 2.98 2.97 VINA VINP 3.3V
LOAD CURRENT (mA)
2.96 100120140 TEMPERATURE (°C)
1.239 100120140 TEMPERATURE (°C)
FREQUENCY VARIATION -0.5 -1.0 -1.5 -2.0
Switching Frequency Input Voltage
FREQUENCY VARIATION 200kHz
Switching Frequency Temperature
SOFT START CURRENT (µA) 200kHz
Soft Start Current Temperature
5.40 5.35 5.30 5.25 5.20 5.15 5.10 5.05 5.00 100120140 TEMPERATURE (°C)
400kHz 100120140 TEMPERATURE (°C)
400kHz
INPUT VOLTAGE
Overcurrent Threshold Input Voltage
THRESHOLD (mV) THRESHOLD (mV) INPUT VOLTAGE 110.0 108.0
Overcurrent Threshold Temperatue
OUTN Drive Impedance Input Voltage
IMPEDANCE INPUT VOLTAGE SINK SOURCE
106.0 104.0 102.0 100.0 98.0 96.0 94.0 92.0 90.0 100120140 TEMPERATURE (°C)
MIC2183
August 2001
MIC2183
OUTP Drive Impedance Input Voltage
IMPEDANCE INPUT VOLTAGE SINK SOURCE
August 2001
MIC2183
MIC2183
Functional Diagram
CDECOUP
VINA
VREF 1.245V
OVERCURRENT COMPARATOR 0.1V
RSENSE
EN/UVLO
BIAS
GAIN
VINP
CURRENT SENSE
fs/4 CONTROL SYNC FREQ/2 FreqOut
OUTP VOUT OUTN COUT
PGND
RESET SLOPE COMPENSATION
PGND
COMPARATOR COMP
0.0002 VREF gain ERROR 100k
0.3V fs/4
FREQUENCY FOLDBACK
SGND
Figure MIC2183 Block Diagram
Functional Characteristics
Controller Overview Functional Description MIC2183 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 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 MIC2183 configured synchronous buck converter. beginning switching cycle, OUTP pulls turns high-side MIC2183
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 MIC2183 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.
August 2001
MIC2183
MIC2183 controller broken down into functions. Control loop operation Current mode control Current limit Reference, enable UVLO FreqOut MOSFET gate drive Oscillator Sync Soft-start 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
MIC2183 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. August 2001
current sense pins (pin (pin noise sensitive signal level high input impedance. traces should short routed close each other. small (1nF) 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 MIC2183 shut down current mode, turn output switching standby mode. enable voltage lower than shutdown threshold turns internal circuitry places MIC2183 micropower shutdown mode. enable voltage between shutdown standby thresholds, internal bias, reference voltages turned soft start forced internal discharge MOSFET. output drivers inhibited from switching. OUTP high state OUTN remains state. Raising enable voltage above standby threshold allows soft start capacitor charge enables output drivers. 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.
MIC2183
MIC2183
MIC2183 1.5V Typical
input supply. VINP must connected same potential. 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. MOSFET Selection P-channel MOSFET must have threshold voltage equal lower than input voltage when used buck converter topology. There limit maximum gate charge MIC2183 will drive. Higher gate charge MOSFETs will slow down turn-on turn-off times MOSFETs. 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 MIC2183. power dissipated gate drive circuitry calculated below: PGATE_DRIVE GATE VINP where: Qgate total gate charge both Pchannel MOSFETs. switching frequency VINP gate drive voltage VINP graph Figure shows total gate charge that driven MIC2183 over input voltage range, different values switching frequency.
Frequency Max. Gate Charge
TOTAL 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 MIC2183 will disabled when input voltage drops back down VINPUT_OFF VINPUT_ENABLE VINPUT_HYST 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 MIC2183 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. VINP (pin supplies drive voltage both gate drive pins, OUTN OUTP. VINP usually connected (VTHRESHOLD VHYST)
500kHz
200kH 300kHz
400kHz
600kHz INPUT VOLTAGE
Figure MIC2183 Frequency Max. Gate Charge Oscillator Sync internal oscillator free running requires external components. allows user select from switching frequencies. level oscillator frequency 400kHz high level oscillator frequency 200kHz. 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, August 2001
MIC2183
MIC2183
oscillator frequency reduced approximately factor Frequency foldback used limit energy delivered output during short circuit fault condition. SYNC input (pin lets MIC2183 synchronize with external clock signal. rising edge sync signal generates reset signal oscillator, which turns side gate drive output. high side drive then turns restarting switching cycle. sync signal inhibited when controller operates frequency foldback. sync signal frequency must greater than maximum specified free running frequency MIC2183. synchronizing frequency lower, double pulsing gate drive outputs will occur. When used, sync must connected ground. maximum recommended output switching frequency 600kHz. Synchronizing higher frequencies possible, however, higher power dissipation internal gate drive circuits will occur. MOSFET gates require charge turn device. average current required MOSFET gate increases with switching frequency. Soft Start Soft start reduces power supply input surge current start controlling output voltage risetime. input surge appears while output capacitance charged slower output risetime will draw lower input surge current. Soft start also used power supply sequencing. soft start voltage applied directly comparator. internal current source used charge soft start capacitor. capacitor discharged when either enable voltage drops below standby threshold voltage drops below UVLO level. part switches duty cycle when soft start voltage zero. soft start voltage rises from 0.7V, duty cycle increases from minimum duty cycle operating duty cycle. oscillator runs foldback frequency (1/4 switching frequency) until feedback voltage rises above 0.3V. risetime output dependent soft start capacitor output capacitance, input output voltage load current. Voltage Setting Components MIC2183 requires resistors output voltage shown Figure
MIC2183 Voltage Amplifier VREF 1.245V VOUT
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. VREF VOUT VREF
Figure output voltage determined equation below. Where: VREF MIC2183 typically 1.245V. VOUT VREF August 2001
Efficiency Considerations Efficiency ratio output power input power. difference dissipated heat buck converter. Under light output load, significant contributors are: VINA supply current VINP supply current, which includes current required switch external MOSFETs 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. 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 capaci tance 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 crease power dissipated resistor. However, will also increase overcurrent limit will require larger MOSFETs inductor components. input capacitors minimize power dissipated capacitors ESR. MIC2183
MIC2183
Package Information
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.020 (0.51) 0.050 (1.27)
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102)
0°-8° 0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
0.0648 (1.646) 0.0434 (1.102)
0.394 (10.00) 0.386 (9.80)
SEATING PLANE
16-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. 2001 Micrel Incorporated
MIC2183
August 2001

MIC2183 Voltage Synchronous Buck Control Preliminary Information

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