Dave McIlroy DCP01B, DCV01, DCP02 three families miniature DC/DC

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Dave McIlroy DCP01B, DCV01, DCP02 three families miniature DC/DC

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OPTIMIZING PERFORMANCE DCP01B, DVC01 DCP02 SERIES UNREGULATED DC/DC CONVERTERS.
Dave McIlroy
DCP01B, DCV01, DCP02 three families miniature DC/DC converters providing isolated unregulated voltage output. fabricated using CMOS/ DMOS process with DCP01B replacing familiar DCP01 family that fabricated from bipolar process. DCP02 essentially extension DCP01B family providing higher power output with significantly improved load regulation, DCV01 tested higher isolation voltage. TECHNOLOGICAL IMPROVEMENTS Transformer drive circuit CMOS/DMOS process represents improvement over bipolar process internal circuits switch much faster. Additionally, transformer drive transistors have characteristically value transistor `on' resistance, (RDS), thus more power transferred transformer. With Bipolar process, transformer drive circuit limited base current available switch power transistors driving transformer, their characteristic current gain (beta) resulting slower turnon time. Consequently, more power dissipated within transistor. This resulted lower overall efficiency, particularly higher output load currents. Self synchronization input synchronizations facility, (SYNCIN) been improved over bipolar devices. eight devices (maximum) have their respective SYNCIN pins connected together, then devices will synchronized. Each device onboard oscillator. This generated charging capacitor from constant current producing ramp. When this ramp passes threshold, internal switch activated that discharges capacitor second threshold before cycle repeated. When several devices connected together, internal capacitors charged simultaneously.
improvements within process such that when device passes threshold during charge cycle, starts discharge cycle. other devices sense this falling voltage likewise initiate discharge cycle that devices discharge together. subsequent charge cycle only restarted when last device finished discharge cycle. OPTIMIZING PERFORMANCE optimum performance only achieved device correctly supported. very nature switching converter, requires power instantly available when `switches' converter DMOS switching transistors, fast edges will create high current demand input supply. This transient load placed input supplied external input decoupling capacitor, thus maintaining input voltage. Therefore, input supply does this transient (this analogy highspeed digital circuits). positioning capacitor critical must placed close possible input pins tracked impedance path. optimum performance primarily dependent factors: Tracking input output circuits minimal loss. ability decoupling capacitors maintain input output voltages constant level. Tracking losses resistance inductance caused tracking minimized ground power plane where possible. that possible, wide tracks reduce losses. several devices being powered from common power source, `star' connected system tracking must deployed; devices must tracked `series', this will cascade losses. position decoupling capacitors important. They must close devices possible order reduce losses.
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Decoupling capacitors capacitors have losses their internal Equivalent Series Resistance, (ESR) lesser degree their Equivalent Series Inductance (ESL). Values latter always easy obtain, however, some manufacturers provide graphs Frequency versus Capacitor Impedance. These will show capacitors impedance falling frequency increased. frequency increased impedance will stop decreasing begin rise. point minimum impedance indicates capacitors resonant frequency. This frequency where components capacitance inductance reactance equal magnitude. Beyond this point capacitor effective capacitor.
Frequency
Where: reactance capacitance, reactance resonant frequency {(XC XL)2 (ESR)2}
Following detection input voltage condition, device switches internal drive circuits until input voltage returns safe value. Then device tries restart. input capacitor still unable maintain input voltage, shutdown reoccurs. This process repeated until capacitor charged sufficiently start device correctly. Otherwise, device will caught loop. Normal start should occur approximately from power being applied device. considerably longer start duration time encountered, likely that either both) input supply capacitors performing adequately. input devices 2.2µF ceramic capacitor will ensure good start performance, remaining input voltage ranges, 0.47µF ceramic capacitors good. tantalum capacitors being considered, close attention must paid value specified, most tantalum capacitors have values. Output Ripple Calculation Example DCP020505: Output voltage Output current 0.4A. full output power, load resistor 12.5. Output capacitor 1µF, 0.1. Capacitor discharge time 800kHz (ripple frequency): tDIS 0.0125µs
RLOAD
FIGURE Capacitor Impedance versus Frequency. however, there 180o phase difference resulting cancellation imaginary component. resulting effect impedance resonant point real part complex impedance namely value ESR. resonant frequency must well above 800kHz switching frequency DCVs. effect cause voltage drop within capacitor. value this voltage drop simply product transient load current: (ESR Where voltage device input, maximum value voltage capacitor during charge, transient load current. other factor that effects performance value capacitance. However, input full wave outputs (single output voltage devices) dominant factor. Input Capacitor effects input decoupling capacitor does have value ESR, then instant power transistors switch voltage input pins will fall momentarily. Should voltage fall below approximately will detect under voltage condition switch drive circuits state. This carried precaution against genuine input voltage condition that could slow down even stop internal circuits from operating correctly. This would result drive transistors being turned long, causing saturation transformer destruction device.
12.5µs VDIS VO(1-EXP(-tDIS/))
VDIS contrast voltage dropped ESR: VESR ILOAD VESR 40mV. Ripple voltage 45mV. Clearly, increasing capacitance will have much smaller effect output ripple voltage than reducing value filter capacitor. DUAL OUTPUT VOLTAGE DCV'S voltage output dual DCPs half wave rectified, therefore, discharge time 1.25µs. Repeating above calculations using 100% load resistance (0.2A output), results shown below:
25µs
TDIS 1.25µs. VDIS 244mV VESR 20mV. Ripple Voltage 266mV. This time capacitor discharging that contributing largest component ripple. Changing output filter 10µF, repeating calculations: Ripple Voltage 45mV. This value composed almost equal components. above calculations given only guide, capacitor parameters usually have large tolerances susceptible environmental conditions.
SBVA013A
OTHER DOCUMENTS RELATING DCP01B, DCV01 DCP02 AB-153: External Synchronization DCP01, Series DC/DC Converters (SBAA035). LAYOUT NOTES Figures illustrate printed circuit board layout tracked conventional (DCP01/02, DCV01), SO-28 surface mount packages (DCP02U). Input power ground planes have been utilized providing impedance path input power. output common been tracked ground plane while tracking positive negative voltage outputs conducted wide tracks order minimize losses.
location decoupling capacitors close proximity their respective pins ensures losses effects tracking inductance thus improving ripple performance. This particular importance input decoupling capacitor this supplies transient current associated with fast switching waveforms power drive circuits. Sync when being used best left floating pad. ground ring annulus connected around will prevent noise being conducted onto pin. Sync being connected more Sync pins then linking track should narrow must kept short length, also other track should close proximity this track this will increase stray capacitance this pin, that will effect performance oscillator.
FIGURE Example Layout, View Component Side.
FIGURE Example Layout, Component Side.
SBVA013A
CON1 COM1 C4-1 C2-1 DCP02xP COM3 SYNC
CON3 SYNC DCP02xU
CON2 COM2 C10-1 C7-1 SYNC DCP02xP COM4
CON4 SYNC DCP02xU
NOTES: Capacitors C2-1, C4-1, C7-1, C9-1 through hole plate components connected parallel with (1206 SMD) respectively. optimum low-noise performance, equivalent series resistance capacitors. connect SYNC jumper (JP1-JP4) SYNC function being used. Connections power input should made with minimum wire 16/0.2 twisted pair, with length kept short. input supply ground respecively represents channel). positive negative outputs, referenced common ground COMx. links used self-synchronization; this facility being used, links should unconnected. R1-R8 power output loads; these external load connected. CON1 CON2 DIL-14; CON3 CON4 SO-28 packages.
FIGURE Example Layout, Schematic Diagram.
SBVA013A
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Dave McIlroy DCP01B, DCV01, DCP02 three families miniature DC/DC

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