MIC2178 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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MIC2178 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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MIC2178 Evaluation Board
MIC2178 Evaluation Board
Ultrahigh-Efficiency Synchronous Buck Converter 5.4V-18V 5V/1A
General Description
Designed portable systems, MIC2178 monolithic, synchronous step-down switching regulator capable 2.5A output current peak efficiency more than 95%. addition, MIC2178 logic-compatible enable that provides near-zero (<5µA) quiescent current off-mode power-critical battery applications. ability switch between skip (pulse-width modulation) mode enables MIC2178 maintain high efficiency over wide output current range. Skip-mode operation enables converter maintain high efficiency light loads turning circuitry pertaining operation, reducing no-load supply current from 600µA. mode offers high efficiency load currents greater than 200mA. Requirements MIC2178 evaluation board requires power supply load resistor).
Operation
Figure shows evaluation board schematic. power-up, MIC2178 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 MIC2178 must mode 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
5.4V 22µF
short time (50ns) until MIC2178 internal circuitry senses that high-side switch fully off. internal synchronous N-channel MOSFET then turns shorting which increases efficiency. Figure shows efficiency skip modes. Precautions MIC2178 protection from reverse polarity power supply. momentary reversal power supply connections cause permanent damage circuit. extreme care with these connections. Also, tantalum capacitors explode operated above their maximum voltage limit reverse biased. safest power MIC2178 start with power supply "zero" volts gradually increase supply voltage. Monitor supply 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,
EFFICIENCY
5.4V Skip
8.4V Skip
8.4V
1000 OUTPUT CURRENT (mA)
Figure Skip- PWM-Mode Efficiency
Enable
1,2,9
50µH MBRS140 60.4k
Flag
SKIP MODE MODE
Mode Sync
PWRGD MIC2178 PGND SYNC COMP SGND
14-17
100µF
VOUT 5V/1A
BIAS
Trace
6.8nF
0.01µF
Figure 5.4V-18V 5V/1A
Micrel, Inc. 1849 Fortune Drive Jose, 95131 (408) 944-0800 (408) 944-0970 http://www.micrel.com
June 2001
MIC2178 Evaluation Board
MIC2178 Evaluation Board
Output Voltage Configuration MIC2178 available 3.3V, 5.0V, adjustable output-voltage versions. MIC2178 evaluation board uses adjustable output version obtain output voltage from 1.24V 15V. following table shows standard resistor values common output voltages:
Output Voltage 3.3V 3.6V (Nearest 28.0k 33.2k 37.4k 60.4k 174k
skip mode, switching action occurs periodically. When output voltage exceeds predetermined threshold, internal MIC2178 P-channel MOSFET turns off, along with majority circuitry, dropping quiescent current from 600µA. During this period, load current supplied output capacitor. When output voltage drops below lower threshold, switching action resumes output capacitor charge replenished. Once output voltage reaches upper threshold, process repeats itself. magnitude hysteresis fluctuates with output voltage determined equation: skip mode, maximum output current limited 290mA. this limit exceeded, output voltage will fall. maintain output regulation currents greater than 290mA, MIC2178 must switched mode just prior system requiring additional power. When system power requirement increases, MIC2178 must mode optimum efficiency. modecontrol switch evaluation board must position during this period. mode, switching waveforms repetitive exhibit subharmonic characteristics. Skip mode produces subharmonic switching frequencies that cause interference problems wireless data acquisition systems. ability force MIC2178 into mode, even load, eliminates these subharmonic frequencies. system insensitive this problem, MIC2177 instead. MIC2177 automatically switches between skip modes, resulting much simpler control scheme. Enable/Shutdown activate MIC2178, enable switch ONposition. power mode-control switch must position proper operation. MIC2178 micropower shutdown, move enable switch position.
Programming resistors used output voltage according equation: 3.3V 5.0V version MIC2178, connect feedback (pin directly output voltage. accomplish this, remove jumper across Frequency Synchronization Sync_Opt (sync option) trace, which normally connected ground, must synchronize MIC2178. 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 MIC2178 system clock from 200kHz 300kHz. Error Flag error-flag output produces low-going signal output voltage drops below programmed value. This output drain grounded-source N-channel MOSFET needs pull-up resistor connected between FLAG input voltage. error flag capable sinking current. output used, connect ground. PWM/Skip-Mode MIC2178 specifically designed controlled intelligent system. Most intelligent systems have ability determine their power needs. When system standby mode, only requires little "flea" power which keeps memory supervisor circuits alive. During this period, MIC2178 should skip mode extend battery life. mode-control switch evaluation board must SKIP position when evaluating low-power efficiency.
Bill Materials
Item Part Number TPSE226M035R0300 TPSD107M010R0100 Dielectric Dielectric MBRS140T3 CTX50-4P MIC2178BWM Manufacturer (803) 448-9411
Motorola (800) 521-6274 Coiltronics (407) 241-7876 Micrel (408) 944-0800
MIC2178 Evaluation Board
June 2001
MIC2178 Evaluation Board
Component Side
Silk Screen (Component Side)
June 2001
MIC2178 Evaluation Board
MIC2178 Evaluation Board
Solder Side
Silk Screen (Solder Side)
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
MIC2178 Evaluation Board
June 2001

MIC2178 Evaluation Board Ultrahigh-Efficiency Synchronous Buck Co

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