Jumper Configurable Watt+ DC-to-DC Converter Fulfills Buck-Boost Motor

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Jumper Configurable Watt+ DC-to-DC Converter Fulfills Buck-Boost Motor

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APEX AN49 AN49
Jumper Configurable Watt+ DC-to-DC Converter Fulfills Buck-Boost Motor Drive Roles
This Application Note describes novel converter design concept that uses SA306-IHZ monolithic threephase switching amplifier1,2. converter depicted schematically Figure thought `black box' module that suitable variety applications such converting volts volts (relative volt input) volts (relative volt input), able deliver minimum amperes combined output. module jumper configurable positive negative input converter. minor circuit change (Figure Note allows module convert volts volts amperes output (representing efficiency), volts converted volts with amperes efficiency). simplicity's sake, design limited scope proven quite usable robust despite limitations listed below, section entitled Miscellaneous Design Notes page This design assumes well regulated voltage input because limited loop gain. output voltage regulation over full output load range with input voltage delta There boost mode current limit circuit included number reasons, which that input diode coupled output output currents excess will exceed diode current/wire bond ratings. Transient load response quite good with full recovery about milliseconds. Efficiencies approximately realized with output approximately with output, depicted application illustrations that follow.
Ext. initial testing Soft Start (Note +Vdd +Vdd 1N4148 1N4148 +Vdd 1N4148 5.6V 1.2k, (Note
(Note 100k
74HC4049 500k Adj. (Note (Note
TLC555
+Vdd
133k
TEMP
TLC555
19.1k
+Vdd 1.3k
SA306-IHZ
DIS2
500k
-Vdd
TLC555
(Note Notes: Nominal phase balance Sgnd ILIM/DIS1 Pgnd 74HC4049 Jumper dashed lines positive converter; (Note jumper solid lines negative converter. (Note optional over-temperature shutdown switch. PGND (phase 37,38,39,40; PGND (phase 48VIN buck, move jumper from X-Z, change jumper, remove R11, changed 1.8K provide current limiting with SA306 unconnected.
74HC4049
Figure.PolarityisEasilySwitched DC-to-DC converter, three terminal module switched from positive negative converter simply interchanging jumpers identified Note (Caution: Make sure A,B,C terminal connections correspond configuration, otherwise SA306-IHZ will destroyed when power applied.) AN49U
http://www.cirrus.com
Copyright Cirrus Logic, Inc. 2008 (All Rights Reserved)
OCT2008 APEX AN49UREV1
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APPliCATiONS
following panel shown number buck, boost motor applications.
Buck-Boost Applications
efficiency
efficiency
Negative Converter
Positive Converter
efficiency
efficiency
Negative Converter
Positive Converter
VDC, efficiency
VDC, efficiency
Buck Negative Converter
Buck Negative Converter
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Motor Drive Applications
MOTOR DRIVE BOARD SA306-IHZ MOTOR
SYSTEM SUPPLY
SYSTEM SUPPLY
MOTOR DRIVE BOARD SA306-IHZ MOTOR
Negative Converter
Battery Applications
LINEAR REGULATOR
Positive Converter
LINEAR REGULATOR
APPLICATION LOADS AMPERES MIN. (COMBINED CURRENT)
Buck Negative Converter
APPLICATION LOADS AMPERES MIN. (COMBINED CURRENT)
Buck Negative Converter
Note: Converters adjustable potentiometer voltage Adjusts from while voltage adjusts from Simultaneously total). maximum output module lesser watts combined output power amperes combined output current. should noted that series loads shown above will divide input voltage converter shuts down (thermal limit, etc). Figure Note reccommended current limiter.
much associated circuitry could replaced with inexpensive micro-controller provide other functions voltage ranges than those shown above applications resulting cost, parts count converter module.
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TheoryofOperation-PWMCircuitry
drive circuit shown Figure comprises three Texas Instruments TLC555 CMOS Timers, well left block Figure Figure serves oscillator. turn, drives which thought pulse width modulators (PWMs). seen Figure inverts input that operates phase with companion, Even though SA306-IHZ three-phase device with three sets MOSFET half bridges, operate this application two-phase switch. Notice bottom Figure that well tied together, transforming operation SA306-IHZ two-phase operation. waveforms shown Figure there underscore fact that phase phases (Ab, (At, Ct), always driven phase with each other. These out-of-phase signals toggle inputs MOSFETs switching amplifier SA306-IHZ (U5). This alternating toggle arrangement distributes power properly within SA306-IHZ die, allowing maximum current throughput reducing ripple current. MaximumOnTime Because Oscillator timing components period oscillator microseconds. maximum time 50%. Raising voltage would provide slight variation. This employed Slow Start circuitry discussed "Charge Dynamics" section that follows. Raising voltage applied raises deadtime increasing threshold these devices time extended. voltage applied through goes time becomes longer.
(phase (phase B&C)
Circuitry Square Wave Generator 45kHz DIS2 Note: Dashed jumper lines Positive Converter; solid jumper lines negative converter SA306-IHZ Switching Amplifier PGND(A&B) VsPGND(C)
Figure circuitry Interface with SA306-IHZ Inputs Simplified
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BoostCircuitry
voltage change technique employed this converter often called `Boost Circuitry'. Each input inductor charged through SA306-IHZ output switch during `charge' interval then synchronously rectified alternate MOSFET output switch during `discharge' interval. another way, energy loaded into inductor then, during discharge interval, delivered current output capacitors and/or load. Because time limited design maximum, voltage delivered output converter limited approximately twice which voltage delivered source. This inherent voltage limiting occurs because `synchronous rectifier' remains during entire `discharge' time then transfers current back from output capacitor into input capacitor. Note that both positive negative versions this converter, current exits SA306-IHZ, either Vs-, entering attached load. Soft Start circuit required confine turn input current transients safe levels occurs time output capacitors ramp This discussed detail Soft Start section, below. jumpers circuit ensure that correct MOSFET switches used charging discharging, thereby programming either positive negative polarity input operation. jumpers must match which they must both `straight through' `crossed'. Caution Both jumpers must reversed, same time, otherwise serious damage occur. Also make sure that A,B,C terminal connections correspond configuration, otherwise SA306-IHZ will destroyed when power applied.
charge dynamics
PositiveConverter positive converter configuration shown Figure inductor charged during interval through bottom MOSFET (Bb) switch. Inductor sees left side Vbat plus right; therefore, current essentially ramp, depicted figure because voltage across inductor essentially constant current integral voltage. Then during interval inductor discharges through MOSFET switch (Bt), exiting through terminal attached load. Again, same occurs MOSFET switches during alternate cycles except their inputs tied together, shown Figure therefore At-Ct Ab-Cb pairs driven unison. NegativeConverter negative converter configuration shown below Figure inductor charged during interval through MOSFET (Bt) switch. When Switch transfers "charge" mode, inductor discharges through bottom MOSFET switch (Bb) into power ground. same occurs MOSFET switches during alternate cycle except their inputs tied together, shown Figure therefore pairs driven unison. BuckNegativeConverter This converter mode same charge dynamics negative converter. difference that power applied terminals removed terminal
SoftStart(Boost Only)
there were constraint when start occurs, input current would become very high because circuit would attempt immediately restore output voltage. order manage this scenario, PWM, which behaves, effect, error amplifier, prevented from overreacting instead duty cycle controlled that duty cycle rises slowly. comes would normally pass through zener diode adjustment potentiometer junction duty cycle node between Resistors R15. Instead Soft Start node connected directly output through Vs+, thereby bypassing output converter sensed network until potential reached.
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(phase
(phase B&C) Discharge Path
(Bt)
Charge Path
(Bb)
SA306-IHZ Switching Amplifier PGND(A&B) VsPGND(C)
Figure charge dynamics Positive converter
(phase (phase B&C) Charge Path
(At) (Bt) (Ct)
(Ab) (Bb) (Cb) SA306-IHZ Switching Amplifier PGND(A&B)
Discharge Path
PGND(C)
Figure charge dynamics Negative converter
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Steady-StateWaveforms
shown Figure when signal from turns current contribution during previous cycle starts decay (Iout waveform). When goes OFF, goes current flows into inductor rising linear fashion depicted. examining actual composite waveform resulting from contributions both phase phase (which behaves single-phase switch driving half inductance microhenries), ripple current reduced. This true because during discharge interval, inductances, connected parallel. effective inductance becomes microhenries. This accounts fact that currents rising falling phase with each other, only partially wash each other out. that delivered current fairly steady amperes, with slight ripple, depicted Figure
Shutdown interval prevent shoot through
Iout
Iout
Figure Phase discharge/charge; Phase charge/discharge AN49U
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Iout
Figure composite Waveforms Phases both delivering current
ThermalProtection
Shown Shown Figure circuit that could added "burp" SA306-IHZ DIS2 external latch) thermal overload detected TEMP
from 7.5k 2N7000 2meg from SA306-IHZ TEMP 1N4148 NOTE: Figure Note current limiter required Buck Negative Converter only limit restart current.
.001
SA306-IHZ DIS2
Figure-ThermalProtectionCircuit optional latch driven SA306-IHZ TEMP output could used shut down converter and/or shut down supply event cooling failure. External current monitoring could also gated same DIS1 latch protect Boost Converter from load faults, etc. Note that should driven through diode when current limiting used (Buck mode only).
OvervoltageProtection (Boost Only)
Over voltage protection Potentiometer that limiting begins when output reaches This essential because there load connected, Boost Circuit power supply, would possible obtain output voltage plus, small potential inductance. This could destroy SA306-IHZ. should maximum resistance when configured Buck mode (Figure Note
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Miscellaneous design Notes
CapacitorsC0andC Capacitors shown bulk values Figures These distributed between power ground terminals provide adequate bypass. OvervoltageShutdown DIS2 employed shut down SA306-IHZ threshold exceeded. Voltage trimming output voltage Adjusting Potentiometer enables trimming output voltage slightly. range small because shift duty cycle (U2, small. output voltage should nominal with output load one-half rated value minimize deviation from nominal under load conditions. MeasuringthePhaseCurrents phase currents measured monitoring voltage pins using scope while Boost Circuitry configured negative converter with output loaded. Input Voltage Limited input voltage above recommended without full characterization application. This fact maximum duty factor output could conceivably rise above rating SA306-IHZ under transient conditions. other Voltage current options should noted that zener could changed zener (approximately) configure converter, example. BuckNegativeConverter Application power should done inrush limiting circuitry nominal input capacitance (input transient "ringing" maximum). References SA306-IHZ Pulse Width Modulation Amplifier Data Sheet, www.cirrus.com 3-Phase Switching Amplifier Application Note #46, www.cirrus.com TLC555 LinCMOS Timer, www.ti.com
coNtActINg cIRRUS LogIc SUPPoRt
Apex Precision Power product questions inquiries, call toll free 800-546-2739 North America. inquiries email, please contact tucson.support@cirrus.com. International customers also request support contacting their local Cirrus Logic Sales Representative. find nearest you, www.cirrus.com
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Jumper Configurable Watt+ DC-to-DC Converter Fulfills Buck-Boost Motor

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