MIC2184 Voltage Buck Control Final Information General Descr

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MIC2184 Voltage Buck Control Final Information General Descr

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MIC2184
MIC2184
Voltage Buck Control Final Information
General Description
Micrel's MIC2184 high efficiency buck control With wide input voltage range 2.9V 14V, MIC2184 used efficiently step voltages down 2-cell battery powered applications, well fixed 3.3V, systems. Efficiencies over achievable over wide range load conditions with MIC2184's control scheme. operating frequency divided raising FREQ/2 VDD. This allows user optimize efficiency versus board space. also allows MIC2184 externally synchronized frequencies below nominal 400KHz. MIC2184 features oscillator output, FreqOut, which used implement simple charge pump voltage applications. output charge pump into gate drive power circuitry VINP pin, allowing enhanced gate drive, hence higher efficiencies, despite input voltages. MIC2184 features shutdown mode, programmable undervoltage lockout, making well suited portable applications. MIC2184 available (small outline package) with junction temperture range range from -40°C +125°C.
Features
Input voltage range: 2.9V >90% efficiency Oscillator frequency 400kHz Frequency divide-by-two Frequency sync 600kHz FrequOut oscillator output allows simple charge pump implementation voltage systems 1.245V reference output Front edge blanking output driver Soft start current mode control shutdown current Cycle-by-cycle current limiting Frequency foldback short circuit protection Adjustable under-voltage lockout narrow-body SOIC 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
OUTP
MIC2184 EFFICIENCY
VINA EN/UVLO FreqOut FREQ/2 COMP VREF SYNC
EFFICIENCY
Si9803DY(x2) 4.7µH
MIC2184
VOUT 2.5V
PGND SGND
220µF(x2) 6.3V
3.3V VOUT 2.5V 200kHz
OUTPUT CURRENT
Adjustable Output Buck Converter
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
August 2001
MIC2184
MIC2184
Ordering Information
Part Number MIC2184BM Output Voltage Adjustable Frequency 400KHz Junction Temp. Range -40°C +125°C Package 16-lead
Configuration
VINA FreqOut COMP SGND EN/UVLO VINP FREQ/2 OUTP VREF PGND SYNC
Lead SOIC
MIC2184
August 2001
MIC2184
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. 1.245V voltage reference available this pin. 0.1µF capacitor should connected from this ground. High current drive high side channel MOSFET. Voltage swing from ground VINP. On-resistance typically 2.5. 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 VREF OUTP FREQ/2 VINP
August 2001
MIC2184
MIC2184
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 (±1%) (±2%) 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 Reference Output(VREF) Reference Voltage (±1.5%) (±2.5%) Reference Voltage Line Regulation Reference Voltage Load Regulation Enable/UVLO Enable Input Threshold UVLO Threshold UVLO Hysteresis Enable Input Current VEN/UVLO (Turn-on threshold) VINA IREF 100µA 1.226 1.213 1.245 1.264 1.276 (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 1.233 1.22 0.04 1.282 1.245 1.257 1.27 Condition Units
MIC2184
August 2001
MIC2184
Parameter Soft Start Soft Start 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 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
Note
Condiion Units
Voltage CSH-CSL trip current limit
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
MIC2184
MIC2184
Typical Characteristics
Quiescent Current Input Voltage
QUIESCENT CURRENT (mA) ISTANDBY INPUT VOLTAGE 200kHz IVINA IVINP
QUIESCENT CURRENT (mA)
Quiescent Current Temperature
IVINA IVINP 3.3V 100120140 TEMPERATURE (°C) 400kHz 200kHz ISTANDBY
400kHz
3.10 3.05 3.00 2.95 2.90 2.85 2.80
Input Voltage
VINA VINP
INPUT VOLTAGE
3.005 3.000 2.995 2.990 2.985 2.980 2.975 2.970
Load
3.08 3.06
Temperature
REFERENCE VOLTAGE
Error Reference Voltage Input Voltage
1.2451 1.2449 1.2447 1.2445 1.2443 1.2441 INPUT VOLTAGE
VINA VINP
3.04 3.02 3.00 2.98 2.96 2.94
LOAD CURRENT (mA)
2.92 100120140 TEMPERATURE (°C)
Error Reference Voltage Temperature
1.246 FREQUENCY VARIATION -0.5 -1.5
Frequency Variation Input Voltage
200kHz SOFT START CURRENT (µA)
Frequency Variation Temperature
200kHz 400kHz
REFERENCE VOLTAGE
1.245 1.244 1.243 1.242 1.241 3.3V 1.24 100120140 TEMPERATURE (°C)
400kHz
INPUT VOLTAGE
TEMPERATURE (°C)
Soft Start Current Temperature
102.0 100.0 THRESHOLD (mV)
Overcurrent Threshold Input Voltage
THRESHOLD (mV) INPUT VOLTAGE
Overcurrent Threshold Temperature
3.3V
CURRENT (µA)
100120140 TEMPERATURE (°C)
98.0 96.0 94.0 92.0 90.0
100120140 TEMPERATURE (°C)
MIC2184
August 2001
MIC2184
OUTP Drive Impedance Input Voltage
IMPEDANCE SINK SOURCE INPUT VOLTAGE
August 2001
MIC2184
MIC2184
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 COUT
RESET SLOPE COMPENSATION
PGND
COMPARATOR COMP
0.0002 VREF gain ERROR 100k
0.3V fs/4 VREF
VREF FREQUENCY FOLDBACK
SGND
Figure MIC2184 Block Diagram
Functional Characteristics
Controller Overview Functional Description MIC2184 BiCMOS, switched mode, synchronous, 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 MIC2184 configured synchronous buck converter. beginning switching cycle, OUTP pulls turns high-side MIC2184
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 MIC2184 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,
August 2001
MIC2184
MIC2184 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
MIC2184 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 MIC2184 shut down current mode, turn output switching standby mode. enable voltage lower than shutdown threshold turns internal circuitry places MIC2184 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.
MIC2184
MIC2184
MIC2184 1.5V Typical
supply. VINP must connected same potential. MOSFET Selection P-channel MOSFET must have threshold voltage equal lower than input voltage when used buck converter topology. There limit maximum gate charge MIC2184 will drive. Higher gate charge MOSFET will slow down turn-on turn-off time MOSFET. Slower transition times will cause higher power dissipation MOSFET higher switching transition losses. MOSFET gate charge also limited power dissipation MIC2184. 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 MIC2184 over input voltage range, different values switching frequency.
Frequency Max. Gate Charge
200x10-9
TOTAL GATE CHARGE
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 MIC2184 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. VREF (pin should decoupled with 0.1µf capacitor placed close pin. must decoupled with ceramic capacitor. capacitor must placed close pin. other capacitor must connected directly ground plane. MOSFET Gate Drive MIC2184 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. VINP (pin supplies drive voltage gate drive pin, OUTP. VINP usually connected input (VTHRESHOLD VHYST) MIC2184
180x10-9 160x10-9 140x10-9 120x10-9 100x10-9 80x10-9 500kHz 60x10-9 40x10-9 20x10-9 0x100 INPUT VOLTAGE 600kHz 200kHz 300kHz 400kHz
Figure MIC2184 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, oscillator frequency reduced approximately factor Frequency foldback used limit energy delivered output during short circuit fault condition. SYNC input (pin lets MIC2184 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 speciAugust 2001
MIC2184
fied free running frequency MIC2184. 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 MIC2184 requires resistors output voltage shown Figure
MIC2184 Voltage Amplifier VREF 1.245V VOUT
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 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. 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: 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 MOSFET. 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.
Figure output voltage determined equation below. Where: VREF MIC2184 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
August 2001
MIC2184
MIC2184
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
MIC2184
August 2001

MIC2184 Voltage Buck Control Final Information General Descr

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