2.5A Synchronous Buck Regulator Micrel MIC2177 200kHz synchronous

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2.5A Synchronous Buck Regulator Micrel MIC2177 200kHz synchronous

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MIC2177
2.5A Synchronous Buck Regulator
Micrel MIC2177 200kHz synchronous buck (stepdown) switching regulator designed high-efficiency, battery-powered applications. MIC2177 operates from 4.5V 16.5V input features internal power MOSFETs that supply 2.5A output current. operate with maximum duty cycle 100% low-dropout conditions. also features shutdown mode that reduces quiescent current less than 5µA. MIC2177 achieves high efficiency over wide output current range switching between skip mode. Operating mode automatically selected according output conditions. Switching frequency preset 200kHz synchronized external clock signal 300kHz. MIC2177 uses current-mode control with internal current sensing. Current-mode control provides superior line regulation makes regulator control loop easy compensate. output protected with pulse-by-pulse current limiting thermal shutdown. Undervoltage lockout turns output when input voltage less than 4.5V. MIC2177 packaged 20-pin wide power package with operating temperature range -40°C +85°C. MIC2178 externally selected skip-mode operation. Data sheets support documentation found Micrel's site www.micrel.com.
Features
4.5V 16.5V input voltage range Dual-mode operation high efficiency 96%) mode 200mA load current Skip mode 200mA load current 100m internal power MOSFETs input 200kHz preset switching frequency quiescent current 1.0mA mode 500µA skip mode shutdown mode 100% duty cycle dropout operation Current-mode control Simplified loop compensation Superior line regulation Current limit Thermal shutdown Undervoltage lockout
Applications
High-efficiency, battery-powered supplies Buck (step-down) dc-to-dc converters Cellular telephones Laptop computers Hand-held instruments Battery Charger
Typical Application
5.4V 22µF
ENABLE SHUTDOWN
1,2,9
Output Efficiency
SYNC 2177-5.0 PGND AUTO COMP SGND BIAS
14-17
50µH MBRS130L
EFFICIENCY
VOUT 5V/1A 100µF
6.8nF
0.01µF
SKIP 1000 2500 OUTPUT CURRENT (mA)
Micrel Inc. 2180 Fortune Drive Jose, 95131 (408) 944-0800 (408) 474-1000 http://www.micrel.com
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Ordering Information
Part Number MIC2177-3.3BWM MIC2177-5.0BWM MIC2177BWM MIC2177-3.3YWM Output Voltage 3.3V 5.0V Adj. 3.3V Switching Frequency 200kHz 200kHz 200kHz 200kHz Temperature Range -40°C +85°C -40°C +85°C -40°C +85°C -40°C +85°C Package 20-Pin Wide SOIC 20-Pin Wide SOIC 20-Pin Wide SOIC 20-Pin Wide SOIC Lead Finish Standard Standard Standard Pb-Free
Configuration
20-Pin Wide SOIC (WM)
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Description
Number Name Function Supply Input: Controller switch supply. Unregulated supply input internal regulator, output switches, control circuitry. Requires bypass capacitor PGND. three pins must connected VIN. Switch (Output): Internal power MOSFET switch output. Both pins must externally connected together. Power Ground: Output stage ground connections. Connect pins common ground plane. Output Voltage Sense (Input): Senses output voltage determine minimum switch current operation. Connect directly VOUT. Automatic Mode: Connect 2.2nF timing capacitor automatic PWM-/skip-mode switching. Regulator operates exclusively mode when pulled low. Feedback (Input): Error amplifier inverting input. adjustable output version, connect external resistive divider output voltage. 3.3V fixed output versions, connect directly output. Compensation: Internal error amplifier output. Connect capacitor series network compensate regulator control loop. Signal Ground: Ground connection control section. Connect pins common ground plane. Frequency Synchronization (Input): Optional clock input. Connect external clock signal synchronize oscillator. Leading edge signal above 1.7V terminates switching cycle. Connect SGND used. Bias Supply: Internal 3.3V bias supply output. Decouple with 0.01µF bypass capacitor SGND. apply external load. Enable (Input): Logic high enables operation. Logic shuts down regulator. allow float.
PGND AUTO
COMP SGND SYNC
BIAS
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Absolute Maximum Ratings
Supply Voltage [100ms transient] (VIN) .18V Output Switch Voltage (VSW). .18V Output Switch Current (ISW).6.0A Enable, Output-Sense Voltage (VEN, VOUT). .18V Sync Voltage (VSYNC).6V
Operating Ratings
Supply Voltage (VIN). 4.5V 16.5V Junction Temperature (TJ) -40°C +125°C
Electrical Characteristics
7.0V; 25°C, bold values indicate -40°C< +85°C, unless noted.
Symbol Parameter Input Supply Current Condition mode, output switching, 4.5V 16.5V skip mode, output switching, 4.5V 16.5V 4.5V 16.5V VBIAS VOUT Bias Regulator Output Voltage Feedback Voltage Output Voltage 16.5V MIC2177 [adj.]: VOUT 3.3V, ILOAD MIC2177 [adj.]: VOUT 3.3V, 16V, 10mA ILOAD MIC2177-5.0: ILOAD MIC2177-5.0: 16V, 10mA ILOAD MIC2177-3.3: ILOAD MIC2177-3.3: 16V, 10mA ILOAD AVOL Feedback Bias Current Error Amplifier Gain Error Amplifier Output Swing Error Amplifier Output Current DMAX Oscillator Frequency Maximum Duty Cycle Minimum On-Time SYNC Frequency Range SYNC Threshold SYNC Minimum Pulse Width ISYNC ILIM SYNC Leakage Current Limit Switch On-Resistance VSYNC 5.5V mode, skip mode high-side switch, low-side switch, 1.0V 1.5V 0.01 Undervoltage Lockout upper threshold lower threshold MIC2177 [adj.] MIC2177-5.0, MIC2177-3.3 0.6V VCOMP 0.8V upper limit Lower limit source sink 3.10 1.22 3.20 3.14 4.85 4.85 4.75 3.20 3.20 3.14 3.30 1.245 4.25 4.15 0.05 3.40 1.27 3.40 3.46 5.15 5.15 5.25 3.40 3.40 3.46 4.35 Units
April 2008
M9999-042108
Micrel, Inc.
Symbol Parameter Output Switch Leakage Enable Threshold Enable Leakage AUTO Threshold AUTO Source Current Minimum Switch Current Operation 1.5V, VAUTO 0.8V VOUT VOUT 5.5V Condition 16.5V 0.01
MIC2177
Units
General Note: Devices sensitive. Handling precautions recommended.
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Typical Characteristics
FREQUENCY (kHz) TEMPERATURE (°C)
Oscillator Frequency Temperature
REFERENCE VOLTAGE
1.252 1.250 1.248 1.246 1.244 1.242 1.240
Reference Voltage Temperature
REFERENCE VOLTAGE MIC2177 [adj.]
3.320 3.315 3.310 3.305 3.300 3.295 3.290 3.285
Reference Voltage Temperature
MIC2177-3.3
1.238 TEMPERATURE (°C)
3.280 TEMPERATURE (°C)
5.030 REFERENCE VOLTAGE 5.020 5.010 5.000 4.990 4.980
Reference Voltage Temperature
AMPLIFIER VOLTAGE GAIN MIC21775.0
19.0 18.5 18.0 17.5 17.0 16.5
Error-Amplifier Gain Temperature
BIAS CURRENT (nA)
Feedback Input Bias Current Temperature
TEMPERATURE (°C)
4.970 TEMPERATURE (°C)
16.0 TEMPERATURE (°C)
CURRENT LIMIT
Current Limit Temperature
High-Side Switch On-Resistance
125°C 85°C 25°C
Low-Side Switch On-Resistance
125°C 85°C 25°C
TEMPERATURE (°C)
INPUT VOLTAGE
INPUT VOLTAGE
SUPPLY CURRENT (mA)
PWM-Mode Supply Current
OUTPUT SWITCHING
EFFICIENCY
3.3V Output Efficiency
EFFICIENCY
Output Efficiency
INPUT VOLTAGE
SKIP 1000 2500 OUTPUT CURRENT (mA)
SKIP 1000 2500 OUTPUT CURRENT (mA)
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Functional Diagram
4.5V 16.5V
UVLO, Thermal Shutdown Output Control Logic ISENSE Amp.
100m P-channel
VOUT 1.245
VOUT
Enable Shutdown
3.3V Regulator ILIMIT Comp. internal supply voltage PWM/ Skip-Mode Select Logic IMIN Comp.
COUT
100m N-channel
PGND
BIAS 0.01µF
Bold lines indicate high current traces
IMIN Thrshld.
SYNC
200kHz Oscillator
CORRECTIVE RAMP
3.3V Output Comp. 10µA
Auto-Mode
AUTO
Skip-Mode Comp.
RESET PULSE
2.2nF
40mV
Comp. Error Amp. VREF 1.245V
COMP
MIC2177 [Adjustable] SGND
April 2008
M9999-042108
Micrel, Inc.
MIC2177 Shutdown Mode MIC2177 low-current shutdown mode that controlled enable input (EN). When logic applied MIC2177 shutdown mode quiescent current drops less than 5µA. Internal Bias Regulator internal 3.3V regulator provides power MIC2177 control circuits. This internal supply brought BIAS bypassing external 0.01µF capacitor. connect external load BIAS pin. designed provide external supply voltage. Frequency Synchronization MIC2177 operates preset switching frequency 200kHz. synchronized higher frequency connecting external clock SYNC pin. SYNC logic level input that synchronizes oscillator rising edge external clock signal. frequency range 220kHz-300kHz, operate with minimum pulse-width 500ns. synchronization required, connect SYNC ground. Low-Dropout Operation Output regulation maintained skip mode even when difference between VOUT decreases below VOUT decreases, duty cycle increases until reaches 100%. this point, P-channel kept several cycles time, output stays regulation until VOUT falls below dropout voltage (dropout voltage P-channel resistance load current). PWM-Mode Operation Refer "PWM-Mode Functional Diagram" which simplified block diagram MIC2177 operating mode with associated waveforms. When operating mode, output P-channel N-channel MOSFETs alternately switched constant frequency variable duty cycle. switching period begins when oscillator generates reset pulse. This pulse resets latch which turns P-channel turns N-channel. During this time, inductor current (IL1) increases energy stored inductor. current sense amplifier (ISENSE Amp) measures P-channel drain-to-source voltage outputs voltage proportional IL1. output ISENSE added tooth waveform (corrective ramp) generated oscillator, creating composite waveform labeled ISENSE timing diagram. When ISENSE greater than error amplifier output, comparator will latch which turns Pchannel turns N-channel. Energy then
Functional Description
Micrel's MIC2177 synchronous buck regulator that operates from input voltage 4.5V 16.5V provides regulated output voltage 1.25V 16.5V. internal power MOSFETs that supply 2.5A load current operates with 100% duty cycle allow low-dropout operation. optimize efficiency, MIC2177 operates skip mode. Skip mode provides best efficiency when load current less than 200mA, while mode more efficient higher current. patented technique allows MIC2177 automatically select correct operating mode load current changes. During operation, MIC2177 uses current-mode control which provides superior line regulation makes control loop easier compensate. switching frequency internally 200kHz synchronized external clock frequency 300kHz. Other features include low-current shutdown mode, current limit, undervoltage lockout, thermal shutdown. following sections details. Switch Output switch output (SW) half H-bridge consisting high-side P-channel low-side N-channel power MOSFET. These MOSFETs have typical on-resistance 100m when MIC2177 operates from supply. Anti-shoot-through circuitry prevents Pchannel N-channel from turning same time. Current Limit MIC2177 uses pulse-by-pulse current limiting protect output. During each switching period, current limit comparator detects P-channel current exceeds 4.7A. When does, P-channel turned until next switching period begins. Undervoltage Lockout Undervoltage lockout (UVLO) turns output when input voltage (VIN) provide sufficient gate drive output MOSFETs. prevents output from turning until exceeds 4.3V. Once operating, output will shut until drops below 4.2V. Thermal Shutdown Thermal shutdown turns output when MIC2177 junction temperature exceeds maximum value safe operation. After thermal shutdown occurs, output will turn until junction temperature drops approximately 10°C.
April 2008
M9999-042108
Micrel, Inc. discharged from inductor decreases until next switching cycle begins. varying P-channel on-time (duty cycle), average inductor current adjusted whatever value required regulate output voltage. MIC2177 uses current-mode control adjust duty cycle regulate output voltage. Currentmode control signal loops that determine duty cycle. outer loop that senses output voltage, other faster inner loop that senses inductor current. Signals from these loops control duty cycle following way: VOUT back error amplifier which compares feedback voltage (VFB) internal reference voltage (VREF). When VOUT lower than nominal value, error amplifier output voltage increases. This voltage then intersects current-sense waveform later switching period which increases duty cycle average inductor current. VOUT higher than nominal, error amplifier output voltage decreases, reducing duty cycle. control loop stabilized ways. First, inner signal loop compensated adding corrective ramp output current sense amplifier. This allows regulator remain stable when operating greater than duty cycle. Second, series resistor-capacitor load connected error amplifier output (COMP pin). This places pole-zero pair regulator control loop. more important item synchronous rectification. mentioned earlier, N-channel output MOSFET turned after P-channel turns off. When Nchannel turns on-resistance enough create short across output diode. result, inductor current flows through N-channel voltage drop across; significantly lower than diode forward voltage. This reduces power dissipation improves efficiency greater than under certain operating conditions. prevent shoot through current, output stage employs break-before-make circuitry that provides approximately 50ns delay from time MOSFET turns other turns result, inductor current briefly flows through output diode during this transition. Skip-Mode Operation Refer "Skip-Mode Functional Diagram" which simplified block diagram MIC2177 operating skip mode associated waveforms. Skip-mode operation turns output P-channel frequency duty cycle that function VIN, VOUT, output inductor value. While skip mode, Nchannel kept optimize efficiency reducing gate charge dissipation. VOUT regulated skipping April 2008
MIC2177 switching cycles that turn P-channel. begin analyzing MIC2177 skip-mode operation, assume skip-mode comparator output high latch output been reset logic This turns P-channel causes increase linearly until reaches current limit 600mA. When reaches this value, current limit comparator sets latch output logic turning P-channel. output switch voltage (VSW) then swings from 0.4V below ground, flows through Schottky diode. discharges energy output de-creases zero. When swings from -0.4V VOUT, this triggers one-shot that resets latch. Resetting latch turns P-channel, which begins another switching cycle. skip-mode comparator regulates VOUT controlling when MIC2177 skips cycles. compares VREF 10mV hysteresis prevent oscillations control loop. When less than VREF 5mV, comparator output logic allowing P-channel turn Conversely, when greater than VREF 5mV, P-channel turned off. Note that this self-oscillating topology which explains switching frequency duty cycle function VIN, VOUT, value unique feature (for pulse-skipping regulator) supplying same value maximum load current value VIN, VOUT, This allows MIC2177 always supply 300mA load current (ILOAD) when operating skip mode. Changing from Skip Mode Refer "Block Diagram" circuits described following sections. MIC2177 automatically changes from skip mode operation when ILOAD drops below minimum value. IMIN determined indirectly detecting when peak inductor current (IL(peak)) less than 420mA. This done minimum current comparator which detects output P-Channel current equals 420mA during each switching cycle. does not, PWM/skip-mode select logic places MIC2177 into skip-mode operation. value IMIN that corresponds IL1(peak) 420mA given following equation:
IMIN Where: inductor ripple current This equation shows IMIN varies function Therefore, user must select inductor value that results IMIN 200mA when IL(peak) 420mA. formulas calculating correct inductor value
M9999-042108
420mA
Micrel, Inc. given "Applications Information" section. Note that varies function input voltage, this also causes IMIN vary. applications where input voltage changes factor two, IMIN will typically vary from 130mA 250mA. During low-dropout operation, minimum current thresh-old circuit reduces minimum value IL1(peak) operation. This compensates decreasing almost zero when difference between VOUT very low.
MIC2177 output comparator determines when VOUT enough regulator change operating modes. detects when feedback voltage below nominal, pulls AUTO ground. When AUTO less than 1.6V, PWM/skip-mode select logic places MIC2177 into operation. external 2.2nF capacitor connected AUTO charged 10µA current source after regulator begins operating mode. result, AUTO stays below 1.6V several switching cycles after operation begins, forcing MIC2177 remain mode during this transition.
Changing from Skip Mode MIC2177 will automatically change from skip mode when ILOAD exceeds 300mA. During skipmode operation, supply 300mA, when ILOAD exceeds this limit, VOUT will fall below nominal value. this point, MIC2177 begins operating mode. Note that maximum value ILOAD skip mode greater than minimum value required mode. This current hysteresis prevents MIC2177 from toggling between modes when ILOAD range 100mA 300mA.
External PWM-Mode Selection MIC2177 forced operate only mode connecting AUTO ground. This prevents skip-mode operation applications that sensitive switching noise.
April 2008
M9999-042108
Micrel, Inc.
MIC2177
PWM-Mode Functional Diagram
4.5V 16.5V
100m P-channel Amp.
VOUT 1.245
100m N-channel
Stop
Corrective 200kHz Oscillator Reset Pulse
Comp. Error Amp. F1.245V MIC2177 [Adjustable] PWM-Mode Signal Path
COMP
Reset Pulse
LOAD
Error Amp. Output
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Skip-Mode Functional Diagram
4.5V 16.5V
Output Control Logic Shot
100m P-channel Amp.
VOUT 1.245
ILIMIT Comp. ILIMIT Thresh. Voltage
Skip-Mode Comp.
F1.245V MIC2177 [Adjustable] Skip-Mode Signal
One-Shot Pulse
April 2008
M9999-042108
Micrel, Inc.
MIC2177
increase significantly. Both these effects will degrade efficiency. formula peak inducto rcurrent IL(peak) ILOAD(max) 300mA maximize efficiency, inductor's resistance must less than output switch on-resistance (preferably 50mor less).
Application Information
Feedback Resistor Selection (Adjustable Version) output voltage configured connecting external resistive divider shown "MIC2177 Block Diagram." ratio determines output voltage. optimize efficiency during output current operation, should less than 20k. However, prevent feedback error input bias current pin, should greater than 100k. After selecting calculate using following formula:
1.245V
Output Capacitor Selection Select output capacitor that value ESR. This parameter determines regulator's output ripple voltage (VRIPPLE) which generated ESR. mentioned "Inductor Selection," maximum value 600mA. Therefore, maximum value
Where: VRIPPLE VOUT Typically, capacitors range 100µF 220µF have less than this maximum value. output capacitor either electrolytic tantalum capacitor, tantalum better choice compact layout operation temperatures below 0°C. voltage rating tantalum capacitor must VOUT, voltage rating electrolytic must VOUT. 600mA VRIPPLE
Input Capacitor Selection input capacitor selected current voltage rating should (equivalent series resistance) electrolytic tantalum capacitor. rule-of-thumb, voltage rating tantalum capacitor should twice value VIN, voltage rating electrolytic should higher than VIN. current rating must equal greater than maximum input ripple current. simple, worst-case formula calculating this current
Tantalum capacitors better choice applications that require most compact layout operation below 0°C. input capacitor must located very close (within inches, 5mm). Also place 0.1µF ceramic bypass capacitor close possible VIN. IRMS(max) ILOAD(max)
Inductor Selection inductor must least minimum value order MIC2177 change from skip mode correct value output current. This minimum value ensures inductor ripple current never exceeds 600mA, calculated using following formula:
VOUT VOUT VIN(max) Where: VIN(max) maximum input voltage general, value least greater than LMIN should selected because inductor values have tolerance ±20%. other parameters consider selecting inductor winding resistance peak current rating. inductor must have peak current rating equal greater than peak inductor current. Otherwise, inductor saturate, causing excessive current output switch. Also, inductor's core loss 8.3µ.3µ
Output Diode Selection operation, inductor current flows through output diode approximately 50ns during dead time when output MOSFET turns other turns skip-mode, inductor current flows through diode during entire P-channel time. correct diode both these conditions diode with reverse voltage rating greater than VIN. must Schottky ultra fast-recovery diode (tR<100ns) minimize power dissipation from diode's reverserecovery charge. Compensation Compensation provided connecting series load COMP pin. This creates pole-zero pair regulator control loop, allowing regulator remain stable with enough frequency loop-gain good load line regulation. higher frequencies pole-zero reduces loop-gain level referred mid-band gain. mid-band gain enough that loop gain crosses with sufficient phase margin. Typical values load 4.7nF 10nF capacitor resistor. Printed Circuit Board Layout well designed board will prevent switching noise ground bounce from interfering with operation
M9999-042108
April 2008
Micrel, Inc. MIC2177. good design takes into consideration component placement routing power traces. first thing consider locations input capacitor, inductor, output diode, output capacitor. input capacitor must placed very close pin, inductor output diode very close pin, output capacitor near inductor. These components pass large high-frequency current pulses, they must short, wide power traces. addition, their ground pins PGND connected ground plane that nearest power supply ground bus.
MIC2177 feedback resistors, compensation network, BIAS bypass capacitor should located near their respective pins. prevent ground bounce, their ground traces SGND should path switching currents returning power supply ground bus. SGND PGND should tied together ground plane that extends under MIC2177.
4.5V 16.5V 22µF
1,2,9
PGND BIAS
50µH MBRS130L
SYNC MIC2177 AUTO COMP SGND
100µF
VOUT 3.3V/1A
0.01
6.8nF
14-17
0.01µF
Micrel MIC2177-3.3BWM Z5UorX7R Ceramic Dielectric Material X7RorNP0 Ceramic Dielectric Material Motorola MBRS130LT3 Coiltronics CTX50-4P, 0.097 Coilcraft HM77-11003, 0.07
Bill Materials
Inductors Capacitors Diodes Transistors
Coilcraft
1102 Silver Lake Cary, 60013 Tel: (708) 639-2361 Fax: (708) 639-1469
Ave. Myrtle Beach, 29577 Tel: (803) 448-9411 Fax: (803) 448-1973
General Instruments (GI)
Melville Park Melville, 11747 Tel: (516) 847-3222 Fax: (516) 847-3150
Siliconix
2201 Laurelwood Santa Clara, 96056 Tel: (800) 554-5565
Coiltronics
6000 Park Commerce Blvd. Boca Raton, 33487 Tel: (407) 241-7876 Fax: (407) 241-9339
Sanyo Video Components Corp.
2001 Sanyo Ave. Diego, 92173 Tel: (619) 661-6835 Fax: (619) 661-1055
International Rectifier Corp.
Kansas Segundo, 90245 Tel: (310) 322-3331 Fax: (310) 322-3332
Technologies
4200 Bonita Place Fullerton, 92835 Tel: (714) 447-2345 Fax: (714) 447-2500
Sprague Electric
60005 Lower Main Sanford, 04073 Tel: (207) 324-4140
Motorola, Inc.
56-126 3102 North Phoenix, 85018 Tel: (602) 244-3576 Fax: (602) 244-4015
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Package Information
20-Pin Wide SOIC (WM)
MICREL, INC. 2180 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. 1999 Micrel, Incorporated.
April 2008
M9999-042108

2.5A Synchronous Buck Regulator Micrel MIC2177 200kHz synchronous

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