MIC2177 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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MIC2177 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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MIC2177 Evaluation Board
MIC2177 Evaluation Board
Ultrahigh-Efficiency Synchronous Buck Converter 5.4V-18V 5V/1A
General Description
Designed battery operated portable systems, MIC2177 Evaluation Board monolithic, synchronous step-down switching regulator capable 2.5A output current peak efficiency more than 96%. addition, MIC2177 logic-compatible 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. Auto mode operation enables converter maintain high efficiency light loads turning circuitry pertaining operation, reducing no-load supply current from less than 600µA. mode offers high efficiency load currents greater than 200mA. MIC2177 evaluation boards available output power levels, 5V/1A 5V/2.5A. Requirements MIAC2177 evaluation board requires 1A/18V power supply load 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 4.4V threshold, 200kHz switching action starts.
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 various output voltages. Precautions MIC2177 protection from reverse 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. safest power MIC2177 start with power supply "zero" volts gradually increase supply voltage. Monitor input current while increasing input voltage. circuits draws excessive current, immediately shut main supply. Then check supply connected properly. This simple procedure avoid most catastrophic failures. Warning: Tantalum capacitors explode improperly connected. Wear safety glasses when operating evaluation board.
5.4V 22µF
ENABLE
1,2,9
MIC2177
33µH MBRS140 30.1k
AUTO MODE
VOUT 5V/1A Fixed 220µF
Mode
MODE
AUTO
PGND BIAS
Sync Trace
SYNC COMP SGND
14-17
10nF
0.01µF
68.1k 30.1k 18.2k
8.06k
JP1A JP1B JP1C JP1D JP1E 1.8V 2.5V 3.3V
Figure 5V/1A Typical Application
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
October 1997
MIC2177 Evaluation Board
MIC2177 Evaluation Board
Output Voltage Configuration MIC2177 available 3.3V, 5.0V, adjustable output-voltage versions. MIC2177 evaluation board uses adjustable output version obtain following industry standard output voltages simply changing programming jumper preferred voltage setting: 1.8V, 2.5V, 3.3V, 5.0V, 6.0V. 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 8.06k
Undervoltage Lockout Undervoltage lockout (UVLO) turns output when input voltage (VIN) provide sufficient gate drive output MOSFETs. prevents output from turning until exceeds 4.4V. Once operating, output will shut until drops below 4.3V. 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. Shutdown Mode MIC2177 low-current shutdown mode that controlled enable input (EN). When logic applied pin, 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 420mA. This done minimum current comparator which detects output P-channel current equals 420mA 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 2.2nF 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 AUTO mode connecting ground. This prevents auto-mode operation applications that sensitive switching noise.
Table Programming Resistor Values Programming resistors used output voltage according equation: 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 allow external synchronization 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 P-channel current exceeds 4.5A peak. does, P-channel turned until next switching period begins.
MIC2177 Evaluation Board
October 1997
MIC2177 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 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
2.2nF
COMP
Comp.
Error Amp. VREF 1.245V
MIC2177 [Adjustable] SGND
October 1997
MIC2177 Evaluation Board
MIC2177 Evaluation Board
1.8V Output Efficiency
3.3V Output Efficiency
EFFICIENCY
EFFICIENCY
Auto 1000 OUTPUT CURRENT (mA)
Auto 1000 OUTPUT CURRENT (mA)
Figure 1.8V Output Efficiency
Figure 3.3V Output Efficiency
2.5V Output Efficiency
Output Efficiency
5.4V
EFFICIENCY
EFFICIENCY
Auto 1000 OUTPUT CURRENT (mA)
Auto
1000 OUTPUT CURRENT (mA)
Figure 2.5V Output Efficiency
Figure Output Efficiency
Bill Materials
Item C3,C5 Part Number TPSE226M035R0300 TPSE227M010R0100 Dielectric Dielectric MBRS140T3 CTX33-3P MIC2177BWM Manufacturer (803) 448-9411 (803) 448-9411
Motorola (800) 521-6274 Coiltronics (407) 241-7876 Micrel (408) 944-0800
MIC2177 Evaluation Board
October 1997
MIC2177 Evaluation Board
Composite Side
Silk Screen (Composite Side)
October 1997
MIC2177 Evaluation Board
MIC2177 Evaluation Board
Solder Side
Silk Screen (Solder Side)
MIC2177 Evaluation Board
October 1997
MIC2177 Evaluation Board
October 1997
MIC2177 Evaluation Board
MIC2177 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. 1998 Micrel Incorporated
MIC2177 Evaluation Board
October 1997

MIC2177 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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