MIC2186 Voltage Control General Description Micrel's MI

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MIC2186 Voltage Control General Description Micrel's MI

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MIC2186
MIC2186
Voltage Control
General Description
Micrel's MIC2186 high efficiency boost control With wide input voltage range 2.9V 14V, MIC2186 used efficiently boost voltages 2-cell battery powered applications, well boost voltages fixed 3.3V, systems. powerful output driver allows MIC2186 supply large output currents with selection proper external MOSFETs. MIC2186 configured operate 100kHz, 200kHz, 400kHz. With it's fixed frequency architecture, easily synchronized drive, MIC2186 ideal noise-sensitive telecommunications applications. MIC2186 also features current shutdown mode 0.5µA programmable undervoltage lockout. manually selectable SKIP Mode allows high efficiencies light load situations. MIC2186 available SOIC QSOP package options with operating range from -40°C 125°C.
Features
Input voltage range: 2.9V output driver Oscillator frequency 100kHz/200kHz/400kHz Frequency sync 600kHz Front edge blanking Current Mode Control Selectable light load SKIP mode 600µA quiescent current (SKIP-Mode) 0.5µA shutdown current Cycle-by-Cycle current limiting Frequency foldback protection Adjustable under-voltage lockout Precision 1.245V reference output SOIC QSOP package options Selectable maximum duty cycle flyback applications power distribution systems Wireless Modems ADSL line cards SLIC power supplies 1-and 2-cell battery operated equipment
Applications
Ordering Information
Part Number Standard Pb-Free MIC2186BM MIC2186BQS MIC2186YM MIC2186YQS Frequency (kHz) Voltage Ambient Temp. Range -40°C +125°C -40°C +125°C Package 16-lead 16-lead QSOP
Typical Application
3.3V 2.2µH MBR2535CT VOUT
120µF
VINA EN/UVLO HIDC FREQ/2 COMP VREF SKIP SYNC
Output Efficiency
VINP MIC2186 OUTN
COUT 150µF(x2)
EFFICIENCY
3.3V OUTPUT CURRENT
Si4404DY (x2)
4.5m PGND SGND
Adjustable Output Boost Converter
Micrel, Inc. 2180 Fortune Drive Jose, 95131 (408) 944-0800 (408) 474-1000 http://www.micrel.com
April 2005
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MIC2186
Configuration
VINA SKIP COMP SGND EN/UVLO VREF VINP FREQ/2 OUTN HIDC PGND SYNC
16-pin Narrow Body 16-pin QSOP (QS)
Description
Number Name VINA SKIP Function Input voltage control circuitry (2.9V 14V). SKIP (Input): Regulator operates mode pulse skipping) when pulled low, skip mode when raised Vdd. There automatic switching between skip mode available this device. Soft start reduces inrush current delays slows output voltage rise time. current source will charge capacitor Vdd. 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 regulates 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 135mV hysteresis. 1.245V reference available this pin. 0.1µF capacitor should connected form this SGnd. input current limit comparator. built offset 100mV between SGnd 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. Maximum source current 0.5mA. 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 bottom current sense resistor terminal CIN. High Duty Cycle. Sets duty cycle frequency along with Freq/2. Logic HIGH sets maximum duty cycle. Logic sets maximum duty cycle. applications section more information. High current drive channel MOSFET. Voltage swing from ground VIN. typically 1.6. Sets duty cycle frequency along with HiDC. applications section more information. Power input voltage gate drive circuitry (2.9V 14V). This normally connected output voltage.
COMP SGND EN/UVLO
VREF
SYNC
PGND HIDC
OUTN FREQ/2 VINP
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MIC2186
Absolute Maximum Ratings (Note
Supply Voltage (VINA, VINP) Digital Supply Voltage (VDD) SKIP Voltage (VSKIP) -0.3V Duty Cycle Voltage (VHIDC) -0.3V Frequency Divider Voltage (VFREQ/2) -0.3V Sync Voltage (VSYNC) -0.3V Comp Voltage (VCOMP) -0.3V Feedback Voltage (VFB) -0.3V Enable Voltage (VEN/UVLO) -0.3V Current Sense Voltage (VCSH) -0.3V Power Dissipation (PD) lead 400mW 85°C lead QSOP 245mW 85°C Ambient Storage Temp -65°C +150°C Rating (Note
Operating Ratings (Note
Supply Voltage (VINA, VINP) +2.9V +14V Operating Ambient Temperature -40°C +85°C Junction Temperature -40°C +125°C PackageThermal Resistance 16-lead 100°C/W 16-lead QSOP 163°C/W
Electrical Characteristics
VINA VINP VOUT 12V, SKIP FREQ/2 HiDC VCSH 25°C, unless otherwise specified. Bold values indicate -40°C +125°C. Parameter Regulation Feedback Voltage Reference (±1%) (±2%) VINA 75mV; (±3%) Feedback Bias Current Output Voltage Line Regulation Output Voltage Load Regulation Input Supply VINA Input Current, mode VINP Input Current, mode VINA Input Current, SKIP mode Shutdown Quiescent Current Digital Supply Voltage (VDD) Digital Supply Load Regulation Undervoltage Lockout VSKIP VSKIP (excluding external MOSFET gate current) VSKIP VEN/UVLO (IVINA IVINP) 0.5mA upper threshold (turn threshold) lower threshold (turn threshold) Reference Output (VREF) Reference Voltage (±1.5%) (±2.5%) Reference Voltage Line Regulation Reference Voltage Load Regulation VinA IREF 100µA 1.226 1.213 1.245 1.264 1.276 2.82 0.03 2.75 2.65 3.18 VINA 75mV 1.233 1.220 1.208 1.245 +0.08 -1.2 1.245 1.258 1.270 1.282 Condition Units
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Parameter 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 SKIP Input SKIP Threshold SKIP Input Current HIDC Input HIDC Threshold 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 Gate Drivers Rise/Fall Time Output Driver Impedance 3300pF source; VINP sink; VINP source; VINP sink; VINP
Note
Condition Units
VEN/UVLO
(Voltage trip current limit)
VSKIP
1.0V, VHIDC 1.0V, VHIDC 1.5V, VHiDC VHiDC VFREQ/2 Measured VHiDC VFREQ/2
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 limitations maximum operating frequency.
Note Note Note
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MIC2186
Typical Characteristics
Quiescent Current Temperature (SKIP Mode)
(mA) IQ(PWM) (mA)
Quiescent Current Temperature (PWM Mode)
3.65 3.55 3.45 VINA 5VDC VINP 12VDC IQVINA+IQVINP
Quiescent Current Input Voltage(PWM Mode)
400kHz
IQ(SKIP) (mA)
VINA 5VDC VINP 12VDC IQVINA+IQVINP
200kHz 100kHz
TEMPERATURE (°C)
3.35 TEMPERATURE (°C)
VINP =12VDC QVINA+IQVINP INPUT VOLTAGE (VINA)
Quiescent Current Input Voltage (PWM Mode)
IQ(PWM) (mA)
(mA)
Quiescent Current Input Voltage (SKIP Mode)
1.2452
REFERENCE VOLTAGE
Reference Voltage Input Voltage
VINP 12VDC 1.245 1.2448 1.2446 1.2444 1.2442 1.244 INPUT VOLTAGE (VINA)
VINP
0.85
VINP 9VDC
VINP
0.75 0.65 0.55
VINP 5VDC
VINP IQVINA IQVINP 400kHz INPUT VOLTAGE (VINA)
VINP 12VDC
INPUT VOLTAGE (VINA)
Reference Voltage Reference Current
1.2451
REFERENCE VOLTAGE
REFERENCE VOLTAGE
Reference Voltage Temperature
1.2454 1.2452 1.2450 1.2448 1.2446 1.2444 1.2442 1.2440 1.2438 1.2436 TEMPERATURE (°C)
Input Voltage
3.10 3.05 3.00 2.95 2.90 2.85 VINP 12VDC 2.80 INPUT VOLTAGE (VINA)
1.245 1.2449 1.2448 1.2447 1.2446 1.2445 1.2444 1.2443
VINP 12VDC VINA 5VDC
VINP 12VDC VINA 5VDC
REFERENCE CURRENT (µA)
Load Current
3.035 3.030 3.025
Temperature
3.08 3.06 3.04
Ienable Venable
VINP 12VDC -40°C VINA 5VDC
IENABLE (µA)
VINP 12VDC VINA 5VDC
VINP 12VDC
3.020 3.015 3.010 3.005 3.000 2.995 IVDD (mA)
VENABLE 20°C 85°C
3.02 3.00 2.98 2.96 2.94 TEMPERATURE (°C)
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Oscillator Frequency Input Voltage
OSCILLATOR FREQUENCY (kHz)
Oscillator Frequency Temperature
OSCILLATOR FREQUENCY (kHz)
Soft Start Temperature
SOFT START CURRENT (µA)
VINP 12VDC
VINP 12VDC VINA 5VDC
4.75 4.70 4.65 4.60 4.55 4.50 4.45 4.40 4.35 4.30 VINP 12VDC VINA 5VDC 4.25 TEMPERATURE (°C)
INPUT VOLTAGE (VINA)
TEMPERATURE (°C)
OVERCURRENT THRESHOLD (mV)
Overcurrent Threshold VINA
VINP 12VDC VINA
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Functional Diagram
CDECOUP
VINA VINP
VREF
EN/UVLO
Bias
VOUT
SKIP
Control fs/4
Overcurrent Reset OutN
COUT
Sync HiDC
Comparator
Corrective Ramp
Reset
Freq/2
PGND
0.1V
Soft Start
Overcurrent Comparator
Gain
Error Amplifier
COMP
RSENSE
PGND
VREF
0.0002 Gain
PGND
100k
0.3V
fs/4
VREF
VREF Frequency Foldback SGND
SGND
Figure MIC2186 Block Diagram
Functional Description
MIC2186 BiCMOS, switched mode multi-topology controller. will operate most side drive topologies including boost, SEPIC, flyback forward. controller impedance driver capable switching large Nchannel MOSFETs. features multiple frequency duty cycle settings. 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 shows block diagram MIC2186 configured boost converter. switching cycle starts when OutN goes high turns side, N-channel MOSFET, MOSFET equal VINP. This forces current ramp inductor. inductor current flows through current sense resistor, Rsense. voltage across resistor amplified combined with internal ramp stability. This signal compared with error voltage signal from error amplifier. When current signal equals error voltage signal, side MOSFET turned off. inductor current then flows through diode, output. MOSFET remains until beginning next switching cycle.
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MIC2186
CDECOUP
VINA VINP
VREF
EN/UVLO
Bias
VOUT
SKIP HiDC
Control
OutN
F/2=H off-time F/2=L off-time
COUT
Freq/2 Sync
PGND
50mV
Soft Start
Current Reset
Skip Current Limit Comparator RSENSE
PGND
COMP
PGND VREF 1.245V
VREF
VREF Hysteresis Comparator SGND
SGND
Figure MIC2186 SKIP Mode Block Diagram
description MIC2186 controller broken down into basic functions. Control Loop Operation SKIP Mode Operation Current Limit MOSFET gate drive Reference, enable UVLO Oscillator Sync Soft start
Control Loop SKIP modes operation MIC2186 operate either (pulse width modulated) SKIP mode. efficiency boost converter improved lower output loads manually selecting skip mode operation. potential disadvantage skip mode variable switching frequency that accompanies this mode operation. occurrence switching pulses depends component values well line load conditions. mode best choice operation higher output loads. mode advantages lower output ripple voltage higher efficiencies higher output loads. Pulling SKIP (pin will force controller operate mode load conditions. Pulling SKIP high will force controller operate SKIP mode.
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MIC2186 SKIP Mode Operation This control method used improve efficiency output loads. block diagram MIC2186 SKIP mode shown Figure power drawn MIC2186 control (IVINA VINA (IVINP VINP). power dissipated significant portion total output power during periods output current, which lowers efficiency power supply. SKIP mode MIC2186 lowers supply current turning portions control drive circuitry when switching. disadvantage this method greater output ripple variable switching frequency. soft start, HiDC Sync pins have effect when operating SKIP mode. SKIP mode, switching starts when feedback voltage drops below lower threshold level hysteresis comparator. OutN goes high, turning Nchannel MOSFET, Current ramps inductor until either current limit comparator hysteretic voltage comparator turns Q1's gate drive. feedback voltage exceeds upper hysteretic threshold, Q1's gate drive terminated. However, voltage exceeds SKIP mode current limit threshold, terminates gate drive that switching cycle. gate drive remains constant period each switching cycle. This time period typically when when high. Figure shows some typical SKIP mode switching waveforms.
I_inductor
Current Efficiency
Mode SKIP Mode
EFFICIENCY
0.05 0.15 INPUT CURRENT
0.25
Figure maximum peak inductor current depends skip current limit threshold value current sense resistor, Rsense. typical 50mV current limit threshold SKIP Mode, peak inductor current
IINDUCTOR_pk
50mV RSENSE
maximum output current SKIP mode depends input conditions, output conditions circuit component values. Assuming discontinuous mode where inductor current starts from zero each cycle, maximum output current calculated below:
IO(max)= RSENSE2
Voltage Divider
I_inductor
Gate Driver
I_inductor
VREF
I_inductor
VCOMP
Gate Drive OutN
TPER
Figure SKIP Mode Waveform SKIP mode current threshold limits peak inductor current cycle. Depending input, output circuit parameters, many switching cycles occur before feedback voltage exceeds upper hysteretic threshold. Once voltage feedback exceeds upper hysteretic threshold gate drive disabled. output load discharges output capacitance causing Vout decrease until feedback voltage drops below lower threshold voltage limit. switching converter then turns gate drive back While gate drive disabled, MIC2186 draws less supply current then while switching, thereby improving efficiency output loads. Figure shows efficiency improvement output loads when SKIP mode selected.
where: Iomax maximum output current output voltage input voltage value boost inductor switching frequency efficiency boost converter Rsense value current sense resistor constant based SKIP mode current threshold (50mV)2 Operation Figure shows typical waveforms mode operation. gate drive signal turns external MOSFET which allows inductor current ramp When MOSFET turns off, inductor forces MOSFET drain voltage rise until boost diode turns voltage clamped approximately output voltage.
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MIC2186
Mode Waveforms
Micrel, Inc. COMP (pin provide access output error amplifier. This allows external components stabilize voltage loop. Current Sensing Overcurrent Protection inductor current sensed during switch time current sense resistor located between source MOSFET ground (Rsense Figure Exceeding current limit threshold will immediately terminate gate drive N-channel MOSFET, This forces operate reduced duty cycle, which lowers output voltage. boost converter, overcurrent limit will protect power supply load during severe overcurrent condition short circuit condition. output short-circuited ground, current will flow from input, through inductor output diode ground. Only impedance source components limits current. mode operation (continuous discontinuous), minimum input voltage, maximum output power minimum value current limit threshold determine value current sense resistor. Discontinuous mode where energy inductor delivered output each switching cycle. Continuous mode operation occurs when current always flows inductor, during both low-side MOSFET times. equations below will help determine current sense resistor value each operating mode. critical value output current boost converter calculated below. operating mode discontinuous output current below this value continuous above this value.
ICRIT VIN2
Conditions: 0.6A
Inductor Current 1A/div
MOSFET gate drive 10V/div Switch Node Voltage (MOSFET Drain) @10V/div VOUT Ripple Voltage @50mV/div
TIME (1µs/div)
Figure mode waveforms MIC2186 uses current mode control improve output regulation simplify compensation control loop. Current mode control senses both 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. simplified current mode control diagram shown Figure
I_inductor
Voltage Divider
I_inductor
Gate Driver
I_inductor
VREF
I_inductor
VCOMP
Gate Drive OutN
TPER
Figure Control Loop block diagram MIC2186 current mode control loop shown Figure inductor current sensed measuring voltage across resistor, Rsense. current sense amplifier buffers amplifies this signal. ramp added this signal provide slope compensation, which required current mode control prevent unstable operation duty cycles greater than 50%. transconductance amplifier used error amplifier, which compares attenuated output voltage with reference voltage. output error amplifier compared current sense waveform block. When current signal rises above error voltage, comparator turns side drive. error signal brought
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where: efficiency boost converter minimum input voltage value boost inductor switching frequency output voltage Maximum Peak Current Discontinuous Mode: peak inductor current
IIND(pk)=
where: maximum output current output voltage minimum input voltage value boost inductor switching frequency efficiency boost converter maximum value current sense resistor April 2005
MIC2186 RSENSE VSENSE IIND(pk)
Micrel, Inc. switching cycle. small filter between current sense current sense resistor help attenuate larger switching spikes high frequency switching noise. Adding filter slows down current sense signal, which effect slightly raising overcurrent limit threshold. MOSFET Gate Drive MIC2186 converter drives side N-channel MOSFET. driver OutN typical source sink impedance. VinP supply gate drive circuit. typically connected output. maximum supply voltage VinP 14V. output voltage greater than desired drive MOSFET with voltage less than Vout, VinP connected input separate supply voltage. MOSFET Selection boost converter, MOSFET approximately equal output voltage. maximum rating MOSFET must high enough allow ringing spikes addition output voltage. VinP supplies N-channel gate drive voltage. threshold voltage N-channel MOSFET must enough operate minimum VinP voltage guarantee boost converter will start maximum amout MOSFET gate charge that driven limited power dissipation MIC2186. power dissipated gate drive circuitry calculated below: P_gate_drive=Q_gate VinP where: Q_gate total gate charge external MOSFET graph Figure shows total gate charge which driven MIC2186 over input voltage range, different values switching frequency. Higher gate charge will slow down turn-on turn-off times MOSFET, which increases switching losses.
Power Dissipation Frequency
100kHz 200kHz 400kHz 500kHz 600kHz
where: Vsense minimum current sense threshold Maximum Peak Current Continuous Mode: peak inductor current equal average inductor current plus half peak peak inductor current. peak inductor current
IIND(pk)= IIND(ave) IIND(pk)=
IND(pp)
where: maximum output current output voltage minimum input voltage value boost inductor switching frequency efficiency boost converter voltage across inductor approximated higher input voltage. However, voltage drop across inductor winding resistance side MOSFET on-resistance must accounted lower input voltages that MIC2186 operates
WINDING RDSON
RSENSE
VSENSE IIND(pk)
where: VSENSE minimum current sense threshold current sense pin, CSH, noise sensitive signal level. current sense voltage measurement referenced signal ground MIC2186. current sense resistor ground should located close ground. Make sure there high currents flowing this trace. trace between high side current sense resistor should also short routed close ground connection. input internal current sense amplifier 30nS dead time beginning each switching cycle. This dead time prevents leading edge current spikes from prematurely terminating April 2005
MAXIMUM GATE CHARGE (nC)
where: Rwinding winding resistance inductor Rdson resistance side switching MOSFET maximum value current sense resistor
Figure MIC2186 freq pdiss External Schottky Diode boost converter topology, boost diode, must rated handle peak average current. average current through diode equal average output current boost converter. peak current calculated current limit section this specification.
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MIC2186 reverse voltage requirement diode MIC2186, Schottky diodes recommended when they used. They have lower forward voltage drop than ultra-fast rectifier diodes, which lowers power dissipation improves efficiency. They also have recovery time mechanism, which results less ringing noise when diode turns off. output voltage circuit prevents Schottky diode, then only ultra-fast recovery diodes should used. Slower diodes will dissipate more power both MOSFET diode. will also cause excessive ringing noise when diode turns off. Reference, Enable UVLO Circuits output drivers enabled when following conditions satisfied: voltage (pin greater than undervoltage threshold. voltage enable greater than enable UVLO threshold. internal bias circuitry generates 1.245V bandgap reference voltage error amplifier voltage internal supply bus. reference voltage MIC2186 buffered brought Vref must bypassed (pin with 0.1uf capacitor. must decoupled ground with ceramic capacitor. enable (pin threshold levels, allowing MIC2186 shut down micro-current mode, turn output switching standby mode. Below 0.9V, device forced into micro-power shutdown. enable between 0.9V 1.5V output gate drive disabled internal circuitry powered soft start voltage forced low. There typically 135mV hysteresis below 1.5V threshold insure part does oscillate ripple voltage input. Raising enable voltage above UVLO threshold 1.5V enables output drivers allows soft start capacitor charge. enable pulled VinA. Oscillator Sync internal oscillator self-contained requires external components. HiDC pins allow user select from three different switching frequencies maximum duty cycles. chart Table shows four combinations that programmed along with typical minimum maximum duty cycles.
Level HiDC Level Switching Frequency 400kHz 200kHz 200kHz 100kHz Maximum Duty Cycle Typical Minimum Duty Cycle
TOFF Skip Mode
Table Minimum duty cycle becomes important boost converter input voltage approaches output voltage. lower duty cycles, input voltage closer output voltage without output rising regulation. frequency foldback mode enabled voltage feedback (pin less than 0.3V. frequency foldback oscillator frequency reduced approximately factor 400kHz setting, oscillator runs 100khz frequency foldback. 200kHz setting oscillator runs approximately 50kHz 100kHz setting, oscillator runs approximately 25kHz. SYNC input (pin allows MIC2186 synchronize with external CMOS clock signal. Depending setting HiDC pin,the output frequency either equal sync input frequency. HiDC level low, output switching frequency half sync frequency. HiDC level high, output switching frequency equal sync frequency. rising edge sync signal generates reset signal oscillator, which turns high-side gate drive output. low-side drive turned restarting switching cycle. sync signal inhibited when controller operates skip mode frequency foldback. sync signal frequency must greater than maximum specified free running frequency MIC2186. synchronizing frequency lower, double pulsing gate drive outputs will occur. When used, sync must connected ground. Table shows minimum recommended sync frequencies different combinations HiDC inputs. Figure shows timing between external sync signal (trace low-side drive (trace high level HiDC pin. Figure shows timing between external sync signal (trace low-side drive (trace level HiDC pin. sync frequency twice output switching frequency.
Level
HiDC Self Oscillating Level Frequency
Minimum Recommended Sync Frequency
Sync Input Frequency fS=output switching frequency fSYNC=sync input frequency fSYNC fSYNC fSYNC fSYNC
400kHz 200kHz 200kHz 100kHz
480kHz 250kHz 480kHz 250kHz
Table
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MIC2186
MIC2186 Sync
Micrel, Inc. output capacitance. Slowing output risetime lowers input surge current. Soft start also used power supply sequencing. soft start cannot control initial surge current boost converter when applied. This surge current caused output capacitance charging input voltage. current flows from input through inductor output diode output capacitors. soft start voltage applied directly comparator. internal current source used charge soft start capacitor. Either UVLO conditions will pull soft start capacitor low. When voltage drops below UVLO threshold When enable drops below 1.5V UVLO threshold 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 until feedback voltage rises above 0.3V. boost converter output voltage equal input voltage before MIC2186 starts switching. ratio Vout/Vin low, voltage feedback will already greater than 0.3V converter begin switching selected operating frequency. risetime output dependent soft start capacitor, output capacitance, input output voltage load current. scope photo Figure show output voltage soft start voltage startup. output voltage initially input voltage less diode drop. After converter enabled output slowly rises minimum duty cycle controller. soft start voltage increases, output voltage rises controlled fashion until output voltage reaches regulated value.
Soft Start
Conditions: HiDC HIGH
Sync Input (Pin
Drive Output (Pin
Figure
MIC2186 Sync
Conditions: HiDC
Sync Input (Pin
Drive Output (Pin
Figure maximum recommended output switching frequency 600kHz. Synchronizing higher frequencies possible, however there some concerns. switching frequency increased, switching period decreases. minimum on-time MIC2186 becomes greater part total switching period. This prevent proper operation approaches Vout also minimize effectiveness current limit circuitry. maximum duty cycle decreases sync frequency increased. Figure shows relationship between minimum/maximum duty cycle frequency.
Max. Duty Cycle Frequency
MAXIMUM DUTY CYCLE
HiDC=H F/2=H HiDC=L F/2=H
HiDC=H F/2=L
HiDC=L F/2=L
Figure Voltage Setting Components MIC2186 requires resistors output voltage shown figure
SYNC FREQUENCY (kHz)
Figure Soft start Soft start reduces power supply input surge current start limiting output voltage risetime. Input surge current occurs when boost converter charges April 2005
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MIC2186
Micrel, Inc. maximum output current. Allow MIC2186 skip mode lower currents. running mode, MIC2186 switch lower frequency. ferrite material inductor core, which less core loss than iron power core. significant contributors power loss higher output loads approximate order magnitude): Resistive on-time losses MOSFET Switching transition losses MOSFET Inductor resistive losses Current sense resistor losses Output capacitor resistive losses (due capacitor's ESR) minimize power loss under heavy loads: Logic level, resistance MOSFETs. Multiplying gate charge resistance gives figure merit, providing good balance between switching resistive power dissipation. Slow transition times oscillations voltage current waveforms dissipate more power during turn-on turn-off side 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 switch faster than those with higher gate charge specifications. same size inductor, lower value will have fewer turns therefore, lower winding resistance. However, using small value will increase inductor current therefore require more output capacitors filter output ripple. Lowering current sense resistor value will decrease power dissipated resistor. However, will also increase overcurrent limit require larger MOSFETs inductor components handle higher currents. output capacitors minimize power dissipated capacitor's ESR.
Voltage Amplifier VREF 1.245V
Figure output voltage determined equation below. Where: Vref MIC2186 nominally 1.245V. Lower values resistance preferred prevent noise from apprearing pin. typically recommended value 10K. Decoupling Capacitor Selection decoupling capacitor used stabilize internal regulator minimize noise pin. Placement this capacitor critical proper operation MIC2186. must next signal ground pins routed with wide etch. capacitor should good quality ceramic. Incorrect placement decoupling capacitor will cause jitter and/or oscillations switching waveform well variations overcurrent limit. minimum 0.1uf ceramic capacitor required decouple Vin. capacitor should placed near connected directly between pins (Vcc) (SGND). 0.1uf capacitor required decouple Vref. should located near Vref pin. Efficiency calculation considerations Efficiency ratio output power input power. difference dissipated heat boost converter. significant contributors light output loads are: VinA supply current. VinP supply current which includes current required switch external MOSFETs Core losses inductor maximize efficiency light loads: gate charge MOSFET smallest MOSFET, which still adequate VREF
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MIC2186
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 SOIC
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.009 (0.2286) 0.025 (0.635) 0.0098 (0.249) 0.0040 (0.102)
0.012 (0.30) 0.008 (0.20)
0.0098 (0.249) 0.0075 (0.190)
SEATING 0.0688 (1.748) PLANE 0.0532 (1.351)
0.196 (4.98) 0.189 (4.80)
0.050 (1.27) 0.016 (0.40) 0.2284 (5.801) 0.2240 (5.690)
16-Pin QSOP (QS)
MICREL INC. 2180 FORTUNE DRIVE JOSE, 95131
(408) 944-0800
(408) 474-1000
http://www.micrel.com
This 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. 2001 Micrel Incorporated
April 2005
M9999-042205

MIC2186 Voltage Control General Description Micrel's MI

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