MIC2179 1.5A Synchronous Buck Regulator General Description

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MIC2179 1.5A Synchronous Buck Regulator General Description

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MIC2179
MIC2179
1.5A Synchronous Buck Regulator
General Description
Micrel MIC2179 200kHz synchronous buck (stepdown) switching regulator designed high-efficiency, battery-powered applications. MIC2179 operates from 4.5V 16.5V input features internal power MOSFETs that supply 1.5A output current. operate with maximum duty cycle 100% low-dropout conditions. also features shutdown mode that reduces quiescent current less than 5µA. MIC2179 achieves high efficiency over wide output current range operating either skip mode. operating mode externally selected, typically intelligent system, which chooses appropriate mode according operating conditions, efficiency, noise requirements. switching frequency preset 200kHz synchronized external clock signal 300kHz. MIC2179 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. MIC2179 packaged 20-lead SSOP package with operating temperature range -40°C +85°C.
Features
4.5V 16.5V input voltage range Dual-mode operation high efficiency 96%) mode 150mA load current Skip mode <150mA load current 150m internal power MOSFETs input 200kHz preset switching frequency quiescent current 1.0mA mode 600µA skip mode shutdown mode Current-mode control Simplified loop compensation Superior line regulation 100% duty cycle dropout operation 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 16.5V
10µF
Output Good Output Skip Mode Mode
16,17
PWRGD
1,2, 19,20
22µH
MBRM120
SYNC
2179-3.3 PGND
BIAS
9-12
100µF 6.3V
VOUT 3.3V/600mA
COMP SGND
6.8nF
0.01µF
4.02k
Pins connected. Pins connected together low-impedance connection.
Micrel, Inc. 2180 Fortune Drive Jose, 95131 (408) 944-0800 (408) 474-1000 http://www.micrel.com
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MIC2179
Micrel, Inc. Part Number Voltage Adj. 3.3V 5.0V Temperature Range -40°C +85°C -40°C +85°C -40°C +85°C Package 20-Lead SSOP 20-Lead SSOP 20-Lead SSOP
Ordering Information
Standard* MIC2179BSM Pb-Free MIC2179YSM
MIC2179-3.3BSM MIC2179-3.3YSM MIC2179-5.0BSM MIC2179-5.0YSM
Standard product will supported Pb-Free PCCN #040004 effective 1-1-2005 pending residual depletion.
Configuration
PGND
PGND PGND
BIAS SYNC SGND SGND
PGND
PWRGD
COMP
SGND
SGND
20-Lead Wide SSOP
Description
Number Name PGND Function Power Ground: Connect pins central ground point. Switch (Output): Internal power MOSFET output switches. PWM/Skip-Mode Control (Input): Logic-level input. Controls regulator operating mode. Logic enables mode. Logic high enables skip mode. allow float. Error Flag (Output): Open-drain output. Active when input below reference voltage (VREF). Feedback (Input): Connect output voltage divider resistors. Compensation: Output internal error amplifier. Connect capacitor series network compensate regulator control loop. Signal Ground: Connect pins ground, PGND. Frequency Synchronization (Input): Optional. Connect external clock signal synchronize oscillator. Leading edge signal above 1.7V terminates switching cycle. Connect SGND used. Internal 3.3V Bias Supply: Decouple with 0.01µF bypass capacitor SGND. apply external load. Enable (Input): Logic high enables operation. Logic shuts down regulator. allow float. Supply Voltage (Input): Requires bypass capacitor PGND. Both pins must connected VIN. internally connected.
9-12
PWRGD COMP SGND SYNC
BIAS
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Absolute Maximum Ratings(1)
Supply Voltage [100ms transient] (VIN) Output Switch Voltage (VSW) Output Switch Current (ISW) 6.0A Enable, Control Voltage (VEN, VPWM) Sync Voltage (VSYNC)
Operating Ratings(2)
Supply Voltage (VIN) .4.5V 16.5V Junction Temperature Range (TJ) -40°C +125°C
Electrical Characteristics(3)
7.0V; 25°C, bold indicates -40°C 85°C; unless noted. Symbol Parameter Condition Input Supply Current mode, output switching, 4.5V 16.5V 3.10 1.22 3.20 3.14 4.85 4.85 4.75 3.20 3.20 3.14 3.90 3.30 1.245 4.25 4.15 1.0V 1.5V mode, high-side switch, VSYNC 5.5V 0.01 0.05 1.27 3.40 3.46 5.15 5.15 5.25 3.40 3.40 3.46 4.35 Units
skip mode, output switching, 4.5V 16.5V VBIAS VOUT Bias Regulator Output Voltage Feedback Voltage Output Voltage 16.5V 4.5V 16.5V
MIC2179 [adj.]: VOUT 3.3V, 16V, 10mA ILOAD MIC2179-5.0: 16V, 10mA ILOAD MIC2179-3.3: 16V, 10mA ILOAD upper threshold lower threshold MIC2179-3.3: ILOAD MIC2179-5.0: ILOAD
MIC2179 [adj.]: VOUT 3.3V, ILOAD
Undervoltage Lockout Feedback Bias Current Error Amplifier Gain Error Amplifier Output Swing Error Amplifier Output Current
MIC2179 [adj.] MIC2179-5.0, MIC2179-3.3 upper limit lower limit source sink 0.6V VCOMP 0.8V
AVOL
Oscillator Frequency Maximum Duty Cycle Minimum On-Time SYNC Frequency Range SYNC Threshold SYNC Minimum Pulse Width
DMAX
ISYNC ILIM
SYNC Leakage Current Limit Switch On-Resistance Output Switch Leakage
skip mode
low-side switch, 16.5V
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MIC2179
Symbol IPWM Parameter Enable Threshold Enable Leakage Threshold Leakage PWRGD Threshold 5.5V VPWM 5.5V Condition 1.09 4.33 2.87 0.01 0.01 1.13 4.54 3.00 0.25 0.01
1.17 4.75 3.13 Units
MIC2179 [adj.]: measured MIC2179-5.0: measured MIC2179-3.3: measured
PWRGD Output PWRGD Leakage
Notes:
ISINK 1.0mA
VPWRGD 5.5V
Exceeding absolute maximum rating damage device. device guaranteed function outside operating rating. Specification packaged product only. General. Devices sensitive. Handling precautions recommended.
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MIC2179
Typical Characteristics
Oscillator Frequency Temperature
REFERENCE VOLTAGE
FREQUENCY (kHz)
1.252 1.250 1.248 1.246 1.244 1.242 1.240
Reference Voltage Temperature
REFERENCE VOLTAGE
MIC2179 [adj.]
3.320 3.315 3.310 3.305 3.300 3.295 3.290 3.285
Reference Voltage Temperature
MIC2179-3.3
TEMPERATURE (°C)
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
MIC2179-5.0
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)
ON-RESISTANCE
CURRENT LIMIT
TEMPERATURE (°C)
ON-RESISTANCE
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
INPUT VOLTAGE
INPUT VOLTAGE
SUPPLY CURRENT (mA)
PWM-Mode Supply-Current
OUTPUT SWITCHING
Skip- PWM-Mode Efficiency
5.4V
EFFICIENCY
8.4V Skip
8.4V
5.4V Skip
OUTPUT CURRENT (mA)
INPUT VOLTAGE
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MIC2179
4.5V 16.5V
Block Diagram
100µF
UVLO, Thermal Shutdown
Output Control Logic
ISENSE Amp.
110m P-channel
VOUT 1.245 VOUT 1.245
Enable Shutdown
3.3V Regulator
VOUT
BIAS
4.02k
110m N-channel
PGND
COUT
0.01µF
internal supply Voltage
ILIMIT Comp.
Connect SGND PGND
Bold lines indicate high current traces
Skip Mode Mode
PWM/ Skip-Mode Select
ILIMIT Thresh. Voltage
Stop
SYNC
Corrective Ramp
200kHz Oscillator
Reset Pulse
Skip-Mode Comp.
Power Good Comp.
Comp.
PWRGD
Output Good
COMP
VREF 1.245V
1.13V
MIC2179 [Adjustable]
SGND
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Micrel, Inc. connect external load BIAS pin. designed provide external supply voltage. Frequency Synchronization MIC2179 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. Power Good Flag power good flag (PWRGD) error flag that alerts system when output regulation. When output voltage below nominal value, PWRGD logic low, signaling that VOUT low. PWRGD open-drain output that sink from pull-up resistor connected VIN. 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 on-resistance load current). PWM-Mode Operation Refer "PWM Mode Functional Diagram" which simplified block diagram MIC2179 operating mode associated waveforms. When operating mode, output P-channel Nchannel 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 sawtooth waveform (corrective ramp) generated oscillator, creating composite waveform labeled ISENSE timing diagram. When ISENSE greater than error amplifier output, comparator will latch which turns P-channel turns N-channel. Energy then 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. MIC2179 uses current-mode control adjust duty cycle regulate output voltage. Current-mode 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
Functional Description
Micrel's MIC2179 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 1.5A load current operates with 100% duty cycle allow low-dropout operation. optimize efficiency, MIC2179 operates skip mode. Skip mode provides best efficiency when load current less than 150mA, while mode more efficient higher current. skip-mode operation selected externally, allowing intelligent system (i.e. microprocessor controlled) select correct operating mode efficiency noise requirements. During operation, MIC2179 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 more detail. 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 150m when MIC2179 operates from supply. Antishoot-through circuitry prevents P-channel N-channel from turning same time. Current Limit MIC2179 uses pulse-by-pulse current limiting protect output. During each switching period, current limit comparator detects P-Channel current exceeds 4.3A. 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 MIC2179 junction temperature exceeds maximum value safe operation. After thermal shutdown occurs, output will turn until junction temperature drops approximately 10°C. Shutdown Mode MIC2179 low-current shutdown mode that controlled enable input (EN). When logic applied MIC2179 shutdown mode, quiescent current drops less than 5µA. Internal Bias Regulator internal 3.3V regulator provides power MIC2179 control circuits. This internal supply brought BIAS bypassing external 0.01µF capacitor.
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MIC2179 (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 N-channel 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 MIC2179 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, N-channel kept optimize efficiency reducing gate charge dissipation. VOUT regulated skipping switching cycles that turn P-channel. begin analyzing MIC2179 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 400mA. When reaches this value, current limit comparator sets latch output logic turning
Micrel, Inc. P-channel. output switch voltage (VSW) then swings from 0.4V below ground, flows through Schottky diode. discharges energy output decreases zero. When swings from -0.4V VOUT, this triggers one-shot that resets latch. Resetting latch turns P-channel, this begins another switching cycle. skip-mode comparator regulates VOUT controlling when MIC2179 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, Pchannel 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 MIC2179 always supply 300mA load current when operating skip mode. Selecting PWM- Skip-Mode Operation skip mode operation selected external logic signal applied pin. logic places MIC2179 into mode, logic high places into skip mode. Skip mode operation provides best efficiency when load current less than 150mA, operation more efficient higher currents. MIC2179 designed used intelligent systems that determine when should operate skip mode. This makes MIC2179 ideal applications where regulator must guarantee noise operation when supplying light load currents, such cellular telephone, audio, multimedia circuits. There important items aware when selecting skip mode. First, MIC2179 start-up only mode, therefore requires logic during start-up. Second, skip mode, MIC2179 will supply maximum load current approximately 300mA, output will drop regulation when load current exceeds this limit. prevent this from occurring, MIC2179 should change from skip mode when load current exceeds 200mA.
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MIC2179
PWM-Mode Functional Diagram
4.5V 16.5V
110m P-channel
VOUT 1.245
Amp.
110m N-channel
Stop
Corrective Ramp
200kHz Oscillator
Reset Pulse
Comp.
COMP
Error Amp. F1.245V
MIC2179 [Adjustable] PWM-Mode Signal Path
SGND
Reset Pulse
ILOAD
Error Amp. Output
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MIC2179
Skip-Mode Functional Diagram
4.5V 16.5V
Output Control Logic
Shot
110m P-channel
Amp.
VOUT 1.245
ILIMIT Comp.
ILIMIT Thresh Voltage
Skip-Mode Comp.
F1.245V
MIC2179 [Adjustable] Skip-Mode Signal Path
SGND
One-Shot Pulse
ILIM
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Micrel, Inc. maximize efficiency, inductor's resistance must less than output switch on-resistance (preferably, less). Output Capacitor Selection Select output capacitor that value ESR. This parameter determines regulator's output ripple voltage (VRIPPLE) which generated ESR. Therefore, must equal less than maximum value calculated specified VRIPPLE (typically less than output voltage) IL(max): VRIPPLE IL(max) Typically, capacitors range 220µF have less than this maximum value. output capacitor electrolytic tantalum capacitor, tantalum better choice compact layout operation temperatures below 0°C. voltage rating tantalum capacitor must VOUT, voltage rating electrolytic must VOUT.
Application Information
Feedback Resistor Selection (Adjustable Version) output voltage programmed connecting external resistive divider shown "MIC2179 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 with following formula: VOUT 1.245V Input Capacitor Selection input capacitor selected current voltage rating should (equivalent series resistance) electrolytic tantalum capacitor. rule 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 ILOAD(max) IRMS(max) Tantalum capacitors better choice applications that require most compact layout operation below 0°C. input capacitor must located very close (within 0.2in, 5mm). Also, place 0.1µF ceramic bypass capacitor close possible VIN. Inductor Selection MIC2179 current-mode controller with internal slope compensation. result, inductor must least minimum value prevent subharmonic oscillations. This minimum value calculated following formula: LMIN VOUT µH/V 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 increase significantly. Both these effects will degrade efficiency. formula peak inductor current IL(max) IL(peak) ILOAD(max) Where: IL(max) VOUT VOUT VIN(max)
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 ultrafast-recovery diode 100ns) minimize power dissipation from diode's reverse-recovery 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 MIC2179. 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.
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MIC2179 feedback resistors, compensation network, BIAS bypass capacitor should located close their respective pins. prevent ground bounce, their ground traces SGND should path switching
Micrel, Inc. currents returning power supply ground bus. SGND PGND should tied together ground plane that extends under MIC2179.
Suggested Manufacturers List
Inductors Coilcraft 1102 Silver Lake Cary, 60013 tel: (708) 639-2361 fax: (708) 639-1469 Coiltronics 6000 Park Commerce Blvd. Boca Raton, 33487 tel: (407) 241-7876 fax: (407) 241-9339 Technologies 4200 Bonita Place Fullerton, tel: (714) 447-2345 fax: (714) 447-2500
Capacitors
Diodes General Instruments (GI) Melville Park Melville, 11747 tel: (516) 847-3222 fax: (516) 847-3150 International Rectifier Corp. Kansas Segundo, 90245 tel: (310) 322-3331 fax: (310) 322-3332 Motorola Inc. 56-126 3102 North 56th Phoenix, 85018 tel: (602) 244-3576 fax: (602) 244-4015
Transistors Siliconix 2201 Laurelwood Santa Clara, 96056 tel: (800) 554-5565
Corp. 17th Ave. South Myrtle Beach, 29577 tel: (803) 448-9411 fax: (803) 448-1943 Sanyo Video Components Corp. 2001 Sanyo Ave. Diego, 92173 tel: (619) 661-6835 fax: (619) 661-1055 Sprague Electric Lower Main 60005 Sanford, 04073 tel: (207) 324-4140
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MIC2179
Package Information
5.40 (0.213) 5.20 (0.205) 7.90 (0.311) 7.65 (0.301)
DIMENSIONS: (INCH)
0.875 (0.034)
7.33 (0.289) 7.07 (0.278)
2.00 (0.079) 1.73 (0.068)
0.22 (0.009) 0.13 (0.005)
0.38 (0.015) 0.25 (0.010)
0.65 (0.0260)
0.21 (0.008) 0.05 (0.002) COPLANARITY: 0.10 (0.004)
1.25 (0.049)
0.95 (0.037) 0.55 (0.022)
20-Lead SSOP (SM)
MICREL INC.
(408) 944-0800 (408) 474-1000 http://www.micrel.com
2180 FORTUNE DRIVE
JOSE, 95131
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
March 2005
M9999-031805

MIC2179 1.5A Synchronous Buck Regulator General Description

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