MIC2177 2.5A Evaluation Board Ultra-High-Efficiency Synchronous B

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MIC2177 2.5A Evaluation Board Ultra-High-Efficiency Synchronous B

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MIC2177 2.5A Evaluation Board
MIC2177 2.5A Evaluation Board
Ultra-High-Efficiency Synchronous Buck Converter 4.5V-16.5V 1.8V-6V/2.5A
General Description
Designed battery-operated portable systems, MIC2177 monolithic, synchronous step-down switching regulator capable 2.5A output current peak efficiency more than 96%. addition, MIC2177 logiccompatible enable that provides near-zero (<5µA) quiescent current off-mode power-critical battery applications. MIC2177 achieves high efficiency over wide output current range switching between auto mode. Auto mode automatically selected according output conditions. enables converter maintain high efficiency output voltage ripple light loads turning circuitry pertaining operation, reducing noload supply current from 500µA. mode offers high efficiency load currents greater than 200mA. MIC2177 evaluation boards come output power levels, 5V/1A, 5V/2.5A. Requirements MIC2177 2.5A board requires 16.5V/3.0A power supply 2.5A load (2.0, 12.5W resistor).
Operation
Figure shows evaluation board schematic. power-up, MIC2177 holds internal power MOSFETs until input voltage reaches undervoltage lockout threshold level. Once input voltage exceeds this 4.5V threshold, 200kHz switching action starts. Note that MIC2177 must have enable switch position start properly.
When internal high-side P-channel MOSFET turns side inductor connected input voltage. During this period, current flows from input through internal P-channel MOSFET, inductor, load. When this MOSFET turns off, voltage drops until clamp diode forward biased. diode conducts only very short time (50ns) until MIC2177 internal circuitry senses that high-side switch fully off. internal synchronous N-channel MOSFET then turns shorting which increases efficiency. Figure shows efficiency auto modes. Precautions MIC2177 protection from reversed voltage polarity being applied input. momentary reversal power supply connections cause permanent damage circuit. extreme care with these connections. Also, tantalum capacitors explode operated above their maximum voltage rating reverse biased. Warning: Tantalum capacitors explode improperly connected. Wear safety glasses when operating evaluation board. safest power MIC2177 start with power supply zero volts gradually increase supply voltage. With load output evaluation board, monitor input current while increasing input voltage. circuits draws excessive input current, immediately shut main supply. Then check supply connected properly. This simple procedure avoid most catastrophic failures. When input bulk capacitors further than 1.0cm from pin, 0.1µF ceramic capacitor should added directly
4.5V 16.5V 22µF 22µF
0.1µF
ENABLE
1,2,9
MIC2177
33µH SS14 30.1k 220µF 220µF
AUTO MODE
VOUT 5V/2.5A Fixed 0.1µF
Mode
MODE
AUTO
PGND BIAS
Sync 6.8nF Trace Jumper
SYNC COMP SGND
14-17
6.8nF
0.01µF
68.1k JP1A 1.8V
30.1k JP1B 2.5V
18.2k JP1C 3.3V
JP1D
7.87k JP1E
Figure 5V/2.5A Evaluation Board Schematic Diagram
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
December 1999
MIC2177 2.5A Evaluation Board
MIC2177 2.5A Evaluation Board
Output Voltage Configuration MIC2177 available 3.3V, 5.0V, adjustable output-voltage versions. MIC2177 evaluation board features adjustable output version configured provide industry standard voltages 1.8V, 2.5V, 3.3V, 5.0V, 6.0V using jumper-selectable programming resistors. Table shows standard resistor values common output voltages:
Output Voltage 1.8V 2.5V 3.3V 30.1k 30.1k 30.1k 30.1k 30.1k (nearest 68.1k 30.1k 18.2k 10.0k 7.87k
Undervoltage Lockout Undervoltage lockout (UVLO) turns output when input voltage (VIN) provide sufficient gate drive output MOSFETs. prevents output from turning until exceeds 4.5V. Once operating, output will shut until drops below 4.35V. Thermal Shutdown Thermal shutdown turns output when MIC2177 junction temperature exceeds maximum value safe operation +125°C). After thermal shutdown occurs, output will turn until junction temperature drops approximately 10°C. Shutdown Mode MIC2177 low-current shutdown mode that controlled enable input (EN). When logic applied MIC2177 shutdown mode quiescent current drops less than 5µA. Changing from Auto Mode MIC2177 automatically changes from automode operation when ILOAD drops below minimum value. IMIN determined indirectly detecting when peak inductor current (IL(peak)) less than 400mA. This done minimum current comparator which detects output P-channel current equals 400mA during each switching cycle. does not, PWM/auto-mode select logic places MIC2177 into auto-mode operation. Refer "Block Diagram." Changing from Auto Mode MIC2177 will automatically change from auto mode when ILOAD exceeds 300mA. During auto-mode operation, MIC2177 supply maximum ILOAD approximately 300mA, when ILOAD exceeds this limit, VOUT will fall below nominal value. MIC2177 will detect this begin operating mode. Note that maximum value ILOAD, auto-mode, greater than minimum value required mode. This current hysteresis prevents MIC2177 from toggling between modes when ILOAD range 100mA 300mA. 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/auto mode-select logic places MIC2177 into operation. external 6.8µF capacitor connected 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. Refer "Block Diagram." External PWM-Mode Selection MIC2177 forced operate only mode connecting AUTO ground. This prevents auto-mode operation applications that sensitive switching noise.
Table Programming Resistor Values Programming resistors used output voltage according equation:
1.245V
MIC2177-3.3 MIC2177-5.0 (3.3V versions), connect feedback (pin directly output voltage. accomplish this, remove jumper across JP2. Frequency Synchronization Sync_Opt (sync option) trace, which normally connected ground, must synchronize MIC2177. sync input requires minimum pulse height 1.7V minimum pulse width 500ns. Standard CMOS logic easily meet this specification when operated from input voltage (VIN). positive going edge triggers synchronization circuitry. duty cycle this pulse vary between 90%, making extremely easy synchronize MIC2177 system clock from 200kHz 300kHz. Low-Dropout Operation Output regulation maintained auto 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 RDS(on) load current). Current Limit MIC2177 uses pulse-by-pulse current limiting protect output. During each switching period, current limit comparator detects peak P-channel current exceeds 4.5A. When does, P-channel turned until next switching period begins.
MIC2177 2.5A Evaluation Board
December 1999
MIC2177 2.5A Evaluation Board
Block Diagram
UVLO, Thermal Shutdown Output Control Logic ISENSE Amp.
100m P-channel
VOUT
1.245
VOUT
Enable Shutdown
3.3V Regulator ILIMIT Comp.
COUT
100m N-channel
PGND
BIAS
0.01µF
internal supply voltage
PWM/ Skip-Mode Select Logic 4.5V IMIN 16.5V Comp.
Bold lines indicate high current traces
IMIN Thrshld.
SYNC
CORRECTIVE RAMP
200kHz Oscillator
3.3V Output Comp. 10µA
Dual-Mode
AUTO
40mV Skip-Mode Comp.
RESET PULSE
6.8nF
COMP
Comp.
Error Amp. VREF 1.245V
MIC2177 [Adjustable] SGND
December 1999
MIC2177 2.5A Evaluation Board
MIC2177 2.5A Evaluation Board
1.8V Output Efficiency
EFFICIENCY
3.3V Output Efficiency
EFFICIENCY
Auto 1000 2500 OUTPUT CURRENT (mA)
Auto 1000 2500 OUTPUT CURRENT (mA)
Figure 1.8V Output Efficiency
Figure 3.3V Output Efficiency
2.5V Output Efficiency
EFFICIENCY EFFICIENCY
Output Efficiency
Auto 1000 2500 OUTPUT CURRENT (mA)
Auto 1000 2500 OUTPUT CURRENT (mA)
Figure 2.5V Output Efficiency
Figure Output Efficiency
Bill Materials
Item Part Number TPSE226M025R0200 TPSE227M010R0100 NP0/COG Dielectric SS14 UP3B-330 (non-shielded) 33µF DS5022P-333 (shielded**) 33µF CDRH127-330MC (shielded**) 33µF MIC2177BWM General Instrument distributor: Tytron (800) 521-6274 Coiltronics (561) 241-7876 (803) 448-9411 Manufacturer
Coil Craft (847) 639-2361
Sumida (408) 982-9660 Micrel (408) 944-0800
required within MIC2177. sensitive applications, recommended that shielded inductor used limit noise interference.
MIC2177 2.5A Evaluation Board
December 1999
MIC2177 2.5A Evaluation Board
Printed Circuit Board Layouts
Component-Side Silk Screen
Component-Side Copper
December 1999
MIC2177 2.5A Evaluation Board
MIC2177 2.5A Evaluation Board
Solder-Side Silk Screen
Solder Side Copper
MIC2177 2.5A Evaluation Board
December 1999
MIC2177 2.5A Evaluation Board
December 1999
MIC2177 2.5A Evaluation Board
MIC2177 2.5A Evaluation Board
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. 1999 Micrel Incorporated
MIC2177 2.5A Evaluation Board
December 1999

MIC2177 2.5A Evaluation Board Ultra-High-Efficiency Synchronous B

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