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Designing Switching Voltage Regulators With TL499A
Patrick Griffith, Hiroshi Miura, Gary Prall ABSTRACT this application report, TL499A wide-range power-supply controller discussed detail. general overview TL499A architecture presents primary functions device features. in-depth study device, used with several external components, showcases versatility limitations device provides thorough understanding criteria required select appropriate values these components. Applying device several basic applications demonstrates usefulness versatility. dc-to-dc converter design example given, using TL499A series regulator that converts step-up switching regulator during primary power-source interruption subsequent restoration. Standard Linear Logic
Contents Introduction TL499A Principles Operation Series Regulator Step-Up Switching Regulator Switching-Current-Limiting Resistor Setting Output Voltage Switching-Regulator Circuit Design Operation Battery Power Load-Current Limitations During Switching-Regulator Operation Recommended Load-Current Tables Recommended Load-Current Table Switching-Regulator Operation (TL499ACP Package) Recommended Load-Current Table Switching-Regulator Operation (TL499ACPS Package) Application-Circuit Example Battery-Backup Circuit Charge-Protection Circuit Switching-Inhibit Circuit Switching-Regulator Design Notes Inductor-Coil Selection Oscillation Frequency Pulse Width Switching Transistor
Trademarks property their respective owners.
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Switching Waveforms Switching Voltage/Current Waveforms With VIN2 VOUT Switching Voltage/Current Waveforms With VIN2 VOUT Switching Waveforms With VIN2 VOUT Switching-Regulator Design-Procedure Flowchart Precautions TL499A Design Circuit Pattern Layout External Surrounding Parts High-Frequency Noise Output Overload Short Circuiting Output References List Figures
TL499A Block Diagram TL499A Basic Configuration Basic Composition Series Regulator Series-Regulation Characteristic Internal Equivalent Circuit Series Regulator Basic Composition Step-Up Switching Regulator Step-Up Switching-Regulator Efficiency Peak Switching Current (IPEAK) Current-Limiting Resistance (RC), IOUT Peak Switching Current (IPEAK) Current-Limiting Resistance (RC), IOUT Negative-Feedback Circuit Output Voltage Discharge Characteristics Nickel-Cadmium Batteries Discharge Characteristics Dry-Cell Batteries Change Voltage (VFL) Output Voltage Battery-Backup Circuit Charge-Protection Circuit Standby-Current Characteristics Switching-Inhibit Circuit Using Switching-Inhibit Circuit Using Pin-2 Sink Current Pin-2 Reference Voltage Inductor Dimensions TL499A Switching Waveforms Switching Output-Voltage Waveform TL499A Switching Voltage/Current Waveform, ILOAD TL499A Switching Voltage/Current Waveform, ILOAD TL499A Switching Voltage/Current Waveform, ILOAD TL499A Switching Voltage/Current Waveform (Maximum Load) TL499A Switching Voltage/Current Waveform (Excessive Load)
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TL499A Switching Voltage/Current Waveform, ILOAD TL499A Switching Voltage/Current Waveform, ILOAD TL499A Switching Voltage/Current Waveform (Maximum Load) Switching-Regulator Design-Procedure Flowchart Recommended Board-Pattern Layout List Tables
Sealed-Type Nickel-Cadmium Storage Batteries (SANYO Electric Co., Ltd.) Compensated-Type Manganese Dry-Cell Batteries (Matsushita Battery Industrial Co., Ltd.) TL499ACP Recommended Load Current During Switching Operation TL499ACP Recommended Load Current During Switching Operation TL499ACP Recommended Load Current During Switching Operation TL499ACP Recommended Load Current During Switching Operation TL499ACP Recommended Load Current During Switching Operation TL499ACPS Recommended Load Current During Switching Operation TL499ACPS Recommended Load Current During Switching Operation TL499ACPS Recommended Load Current During Switching Operation TL499ACPS Recommended Load Current During Switching Operation TL499ACPS Recommended Load Current During Switching Operation Standard Drum-Core-Type Coil Characteristics
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Introduction
TL499A integrated circuit designed provide wide range adjustable regulated supply voltages. regulated output voltage from adjusting external resistors. When TL499A coupled ac-line power through step-down transformer, operates series dc-voltage regulator maintain regulated output voltage. With addition battery from inductor, filter capacitor, resistors, TL499A operates step-up switching regulator during ac-line power failure. main function blocks internal composition series regulator switching regulator, which used independently. However, TL499A best suited battery backup system after power failure. Optimal conversion efficiency obtained inserting suitable resistor between switching-current control terminal ground, thereby restricting switching current.
TL499A Principles Operation
block diagram TL499A shown Figure TL499A consists series regulator, switching regulator, voltage-control circuit. TL499A configured regulate output voltage between minimum maximum choosing appropriate values external resistors, (see Figure addition, input voltage range during step-up switching-regulator mode between
Startup Voltage Sense Blocking Diode OUTPUT
Switching Regulator
(PWR) CURRENT CTRL
Current Sense SERIES Startup
Figure TL499A Block Diagram
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SERIES
TL499A SERIES CURRENT CTRL OUTPUT (PWR)
0.01
OUTPUT
Figure TL499A Basic Configuration
Series Regulator
basic block diagram series regulator shown Figure name series regulator originates control element used regulation. Modulating series element regulates output voltage. Generally, this series element transistor, operates like variable resistance. change input voltage changes equivalent conductance series element. product this equivalent conductance load current produces potential voltage drop compensate change input voltage.
VOUT Vref
VREF
Figure Basic Composition Series Regulator
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When considering basic configuration series regulator, equivalent series resistance (RS) derived following equations. Output voltage (VOUT) given DIFF LOAD
LOAD LOAD LOAD LOAD LOAD
Change series resistance (RS), terms change input voltage, given
Change series resistance (RS), terms change load current, given
regulation characteristic over series input voltage shown Figure
VOUT VOUT Output Voltage
VOUT VOUT VOUT VIN1 Series Input Voltage
Figure Series-Regulation Characteristic internal equivalent circuit series-regulator block TL499A shown Figure series regulator TL499A operates exactly same basic series regulator shown Figure internal reference voltage 1.26 (typical). external resistor divider (RE1 RE2) sets output voltage level. output voltage series regulator between regulation possible output currents within allowable total power-dissipation range. recommended that value resistor used.
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VOUT
VIN1 Startup Vref
Figure Internal Equivalent Circuit Series Regulator
Step-Up Switching Regulator
operating principle switching voltage regulator with high conversion efficiency understood analyzing basic configuration step-up switching regulator shown Figure
IPEAK
VOUT
Switching Control Circuit
IOUT
Figure Basic Composition Step-Up Switching Regulator duty cycle switching transistor (Q1) controlled switching frequency control circuit. alternates between states during operation. obtain stable output voltage series regulator, pass transistor, which control element series regulator, operates continuously. switching regulator, switching transistor alternates between states. Because this transistor always saturated state completely other times, voltage loss associated with switching transistor very small compared voltage loss attributed pass transistor series regulator. When turned beginning charge cycle, voltage (VIN input voltage saturation voltage switching transistor) developed across both ends inductor inductor current increases linearly. charge cycle, current through inductor peak value. Peak current expressed
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PEAK
charge cycle, switching transistor (Q1) turned off, regulator goes into discharge mode. diode (D1) acts flywheel diode provides current path from inductor output. inductor current reduced linearly discharged. ratio charge/discharge time proportional input-to-output voltage difference divided input voltage. CHARGE DISCHARGE
voltage difference increases, discharge time decreases becomes smaller than charge time. DISCHARGE PEAK
switching losses considered negligible, conversion efficiency ideal step-up switching regulator 100% (10) (11) (12) 100% (13)
conversion efficiency TL499A during switching-regulator operation maximized changing value current-limiting resistance, example characteristic curve conversion efficiency versus shown Figure
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VOUT VOUT VOUT VOUT VOUT VOUT
Efficiency
VIN2 ILOAD 1,000 10,000
Current-Limiting Resistance
Figure Step-Up Switching-Regulator Efficiency
Switching-Current-Limiting Resistor
switching current TL499A restricted inserting resistor (RC) between switching-current control terminal (pin (pin (see Figure exact value depends desired conversion efficiency requirements (VIN, VOUT, IOUT, etc.) application circuit. Graphs maximum peak switching current versus shown Figure IOUT Figure IOUT mA). TL499A internal current-limiting thermal-shutdown circuitry that turns switching transistor junction temperature becomes high.
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1600 1400 IPEAK Peak Switching Current 1200 1000
255C VIN2 VOUT ILOAD
Current-Limiting Resistance
Figure Peak Switching Current (IPEAK) Current-Limiting Resistance (RC), IOUT
1200 1100 IPEAK Peak Switching Current 255C VIN2 VOUT ILOAD
1000
Current-Limiting Resistance
Figure Peak Switching Current (IPEAK) Current-Limiting Resistance (RC), IOUT
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Setting Output Voltage
basic configuration circuit TL499A shown Figure output voltage negative-feedback circuit shown Figure TL499A internal reference voltage 1.26 (typical). Using this internal reference voltage external resistors RE2, possible desired output voltage. recommended that value used. Figure used select appropriate value provide desired output voltage. error amplifier controls output voltage detecting changes load feeding back information either series regulator bias circuit switching regulator, depending mode which TL499A operating.
VCC+
Vref
VOUT Vref
Figure Negative-Feedback Circuit
255C VIN2 ILOAD
VOUT Output Voltage
Figure Output Voltage
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Switching-Regulator Circuit Design
Operation Battery Power
design procedure acquiring optimal efficiency shown Figure When TL499A operating switching-regulator mode, battery supplies power load through inductor. Over time, battery voltage begins decay and, result, magnitude switching current through inductor increases with time. inductor current increases, battery discharges more rapidly. standard characteristics typical nickel-cadmium storage battery shown Table Figure standard characteristics typical manganese dry-cell storage battery shown Table Figure make TL499A supply continuous output power reasonable amount time during switching-mode operation battery power, necessary select appropriate value taking into consideration discharge characteristic battery load regulator. recommended value between
Load-Current Limitations During Switching-Regulator Operation
Just TL499A used with broad combination input output voltages that affect maximum-value output current, output current changes with values Although value must within range TL499A still achieve stable efficient operation with little output voltage ripple. Maximum load currents, function different input output voltage combinations, shown Tables through current value indicated tables value load current when 10-mV decrease reference voltage (pin measured, load current increased gradually from starting value load current increased beyond specification, load regulation worsens, expected output voltage longer achieved. When battery cannot supply peak switching current (see Figures TL499A cannot start switching operation. Also, TL499A must connected battery capable supplying sufficient current when TL499A used applications other than changing between series- switching-regulator operation (battery backup operation), such when using TL499A only switching-mode operation.
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Table Sealed-Type Nickel-Cadmium Storage Batteries (SANYO Electric Co., Ltd.)
Standard Charge Model Nominal Voltage Nominal Capacity (mAh) Rapid Charge Current (mA) Time (hour) Internal Resistance (mW) With Tube Diameter (mm) 10.5 13.0 14.5 12.0 10.5 17.0 14.5 17.0 14.2 14.2 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 Height (mm) 16.0 14.5 17.0 42.5 29.5 44.5 17.0 30.0 28.0 50.0 48.7 26.0 34.0 30.0 43.0 50.0 61.0 Outside Size Base Battery Diameter (mm) 10.0 12.5 14.0 11.5 10.0 16.5 14.0 16.5 13.8 13.8 22.0 22.0 25.2 22.0 25.2 32.3 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 Height (mm) 15.0 14.0 16.7 41.8 28.5 43.7 16.3 29.5 27.8 49.5 48.2 25.8 33.0 29.8 42.0 49.0 60.0 -0.2 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.2 -0.3 -0.3 -0.2 -0.3 -0.2 -0.3 -0.3 -0.4 Approx. Weight
Current (mA)
Time (hour)
N-50AAA N-75P N-110AA N-120TA N-150N N-200AAA N-200A N-270AA N-500A N-600AA N-600AAL N-650SC N-1000SC N-1100C N-1300SC N-2000C N-4000D N-6PT
1000 1100 1300 2000 4000
14~16
55.0 45.0 30.0 34.0 27.0 21.0 20.0 15.0 12.0 12.0 210.0
17.0 26.0 48.5
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Battery Voltage
Conditions: Charge Hours Discharge Temperature 205C
Discharge Capacity
Figure Discharge Characteristics Nickel-Cadmium Batteries
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Table Compensated-Type Manganese Dry-Cell Batteries (Matsushita Battery Industrial Co., Ltd.)
MODEL NUMBER OUTSIDE SIZE (mm) WEIGHT NOMINAL VOLTAGE NOMINAL CAPACITY hours day, intermittent electrical discharge typical 56.5 hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical 23.5 hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical 18.2 hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours hours day, intermittent electrical discharge typical hours
SUM-1 (NG)
34.0 61.5
SUM-2 (NG)
26.0 50.0
SUM-3 (NG)
14.5 50.5
SUM-1 (DG)
34.0 61.5
SUM-2 (DG)
26.0 50.0
SUM-3 (DG)
14.5 50.5
Voltage
Voltage
SUM-1 Self-Sustaining Time hours
SUM-2 Self-Sustaining Time hours
Figure Discharge Characteristics Dry-Cell Batteries
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Recommended Load-Current Tables
Recommended Load-Current Table Switching-Regulator Operation (TL499ACP Package)
maximum output current values various combinations input output voltages TL499ACP shown Tables 3-7. Table TL499ACP Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
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Table TL499ACP Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE (rin 25°C LOAD CURRENT (mA)
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
Table TL499ACP Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
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Table TL499ACP Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
Table TL499ACP Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
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Recommended Load-Current Table Switching-Regulator Operation (TL499ACPS Package)
maximum output current values various combinations input output voltages TL499ACPS shown Tables 8-12. Table TL499ACPS Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
Table TL499ACPS Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
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Table TL499ACPS Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
Table TL499ACPS Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
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Table TL499ACPS Recommended Load Current During Switching Operation
VOUT OUTPUT VOLTAGE LOAD CURRENT (mA)
(rin 25°C
VIN2 INPUT VOLTAGE should satisfy following conditions: 70°C, 85°C. NOTE: VOUT VIN2
Application-Circuit Example
Battery-Backup Circuit
TL499A operates series regulator when input voltage VIN1 32.0 present output voltage series mode slightly higher than switching mode. This because feedback voltage series-regulator circuit higher than feedback voltage switching circuit. This output voltage difference (VFL), change voltage, typically output voltage, high change voltage gives priority series operation over switching operation conserve battery power while line power available. While series-regulator circuit operating, switching circuit state, battery power used. characteristics change voltage versus output voltage shown Figure battery-backup circuit diagram, which used with power-supply transformer, shown Figure
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VIN2 IPEAK ILOAD VIN1 VOUT
Change Voltage
VOUT Output Voltage
Figure Change Voltage (VFL) Output Voltage
VIN1 VIN2 32.0
VOUT
TL499A
Figure Battery-Backup Circuit
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Charge-Protection Circuit
Because voltages excess recommended maximum appear input TL499A when fault conditions occur line when battery removed, inserting Zener diode protection (see Figure recommended. standby current required this circuit shown Figure
VIN1
VIN2
TL499A
Figure Charge-Protection Circuit
Standby Current
VIN2 Switching Input Voltage
Figure Standby-Current Characteristics
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Switching-Inhibit Circuit
shown Figure switching circuit TL499A turned applying external voltage approximately higher than switching output voltage However, this method causes heavy current load external voltage source results reduction voltage under heavy load. external power supply with current capacity greater than load current needed, this practical application. Another method shown Figure circuit Figure turns switching circuit applying voltage above typical 1.26-V internal reference voltage current that flows into independent load. recommended voltage range from (VREF (VIN1 characteristic graph pin-2 sink current versus externally applied shutdown voltage shown Figure
TL499A VIN2 Input
Figure Switching-Inhibit Circuit Using
Input
VIN1
VOUT
TL431CLP
VIN2
Figure Switching-Inhibit Circuit Using
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IREF Pin-2 Sink Current
VREF Pin-2 Reference Voltage
Figure Pin-2 Sink Current Pin-2 Reference Voltage
Switching-Regulator Design Notes
Inductor-Coil Selection
designer must ensure that inductor used with TL499A saturated peak switching current about that good frequency characteristic. inductor high, produces ringing switching waveform, efficiency decreases. addition, designer should choose inductor with relatively internal series resistance. Although beneficial increase internal resistance coil when ripple noise excessive, switching efficiency will optimal. Some inexpensive drum-core coils available with resistance good frequency characteristic. Other types coils, such ring core, have internal resistance characteristics, they comparatively expensive. characteristics some standard drum-core coils shown Table dimensional diagram these drum coils given Figure
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Table Standard Drum-Core-Type Coil Characteristics
CHARACTERISTIC Number turns inductance load Measurement frequency Core Wire Coil processing Direct current resistance Form size Core diameter, Core height, Lead Lead Lead pitch, Lead diameter, ±0.5 MODEL NUMBER DR4-500K (1-2) <10%) 2.52 Drum core 0.12 2-UEW High-frequency varnish K-500K (1-2) <10%) 2.52 Drum core High-frequency varnish 0.092 K-800K (1-2) <10%) 2.52 Drum core 0.35 High-frequency varnish 0.142 K-101K (1-2) <10%) Drum core High-frequency varnish 0.135 K-141K (1-2) <10%) Drum core 0.35 High-frequency varnish 0.21
Made Kyodo News Industry Co., Ltd. Contact: 1-14-1, Nishi-Kanagawa-ku, Yokohama-shi Postcode Phone 045(324)2244
Figure Inductor Dimensions
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Oscillation Frequency Pulse Width Switching Transistor
waveform switching transistor TL499A shown Figure upper waveform switching transistor collector voltage, lower waveform inductor peak switching current. waveforms divided roughly into three portions:
Transistor time charging energy into inductor: Transistor time discharging energy into output load: tOFF Transistor quiescent time stopping energy change: tQUI
Note following switching characteristics TL499A: load current (ILOAD) increased, duration pulse sequence (the number pulses between quiescent time periods) increases. Therefore, duration quiescent time decreases. And, load current increased further, peak voltage pulse sequence decreased, becomes impossible maintain specified output voltage. collector voltage switching transistor during quiescent time equal switching input voltage. error amplifier determines duration quiescent time (tQUI) switching transistor. output voltage increased, duration pulse sequence also increases. switching input voltage lowered, duration pulse sequence increases.
tQUI
tOFF
Figure TL499A Switching Waveforms
Switching Waveforms
Some switching transistor collector voltage inductor peak switching-current waveforms shown Figures 23-31 various input output conditions.
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Switching Voltage/Current Waveforms With VIN2 VOUT
Current Voltage
Time VIN2 VOUT 10.0 mF/35 ILOAD Y-axis scale: V/div X-axis scale: ms/div
Figure Switching Output-Voltage Waveform
Switching Voltage/Current Waveforms With VIN2 VOUT
Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
Figure TL499A Switching Voltage/Current Waveform, ILOAD
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Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
Figure TL499A Switching Voltage/Current Waveform, ILOAD
Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
Figure TL499A Switching Voltage/Current Waveform, ILOAD
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Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
NOTE: under these conditions recommended.
Figure TL499A Switching Voltage/Current Waveform (Maximum Load)
Current
Voltage
Time VIN2 VOUT 7.80 (Target VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
NOTE: under these conditions recommended.
Figure TL499A Switching Voltage/Current Waveform (Excessive Load)
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Switching Waveforms With VIN2 VOUT
Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
Figure TL499A Switching Voltage/Current Waveform, ILOAD
Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
Figure TL499A Switching Voltage/Current Waveform, ILOAD
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Current
Voltage
Time VIN2 VOUT 15.0 mF/35 ILOAD 15.0 X-axis scale: ms/div Upper Y-axis scale: V/div Lower Y-axis scale: A/div
NOTE: under these conditions recommended.
Figure TL499A Switching Voltage/Current Waveform (Maximum Load)
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Switching-Regulator Design-Procedure Flowchart
flowchart assist with circuit design using TL499A shown Figure
Start Notes Determine output voltage (VOUT) VOUT CONSTANT
Determine output current (IOUT)
IOUT CONSTANT
Determine maximum continuous operating time using battery power
appropriate battery selected selected.
Determine battery input voltage (VIN)
CONSTANT
Select coil that provides maximum conversion efficiency (see Table
inductor (L), value between recommended. filter capacitor (CL), value recommended. conversion efficiency about when using value between When input output voltage values external surrounding parts constant, limit maximum output current value where quiescent time period (tQUI) exists switching waveform, shown Figure circuit Figure Conversion efficiency:
Measure switching current with using large direct-current-capable power supply (with output current capacity Compute conversion efficiency.
efficiency maximized, increase value switching current restriction resistance, 100-W steps. Measure switching current, recompute conversion efficiency.
100%
Does output voltage output current regulator meet requirements?
Choose smaller resistance value
After taking electric discharge characteristic battery into consideration, necessary determine value small value between
Figure Switching-Regulator Design-Procedure Flowchart
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Precautions TL499A Design
take full advantage features TL499A, consider following sections.
Circuit Pattern Layout
Because high-frequency peak current flows during switching operation, external surrounding parts RE1, RE2, etc.) (see Figure must arranged close possible mounted circuit with large ground pattern thick lead width (see Figure 33). large ground plane provide good heat dissipation.
Figure Recommended Board-Pattern Layout
External Surrounding Parts
Coil µH)]. Coils have most influence efficiency performance switching regulator. series resistance coil ideal (0.1 less), this large direct-current resistance allow switching operation start will create problems. Decoupling capacitor (CL). Although large capacitor value greatly enhances output voltage ripple removal, large, inrush current time switching start-up become excessive cause TL499 start during switching operation. Increasing value decoupling capacitor (CL) between necessary, depending case. Path capacitor (0.05 µF)]. This capacitor inserted between pins reduce output ripple voltage much possible. Switching-current-limiting resistance (RC). this resistor within limits this value small, switching current increases greatly efficiency worsens. this value large, stabilized output voltage will achieved. Input capacitor (CIN). When change power-supply voltage from series mode switching mode large, distance between battery power supply separated large distance, input surge capacitor between ground recommended prevent large, sudden inrush current Line-voltage sensing switch (S). When using line-voltage sensing switch, which contact resistance very small. switching regulator start contact resistance large.
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High-Frequency Noise
TL499A fixed values input output voltage, oscillation frequency switching transistor increases with increasing load current. Because frequency range switching noise broad, noise induced surrounding components. help reduce effects switching noise:
Keep coil, capacitor wires short possible, large ground pattern (use recommended pattern Figure 33). Keep away from nodes with high input impedance antennas. reduce load current change component values external surrounding parts, needed. Ensure that path capacitor between pins securely inserted and, also, insert capacitor switching input side (pin Consider direction magnetic field generated coil, shield using screen, plate, etc.
Output Overload Short Circuiting Output
When output overloaded, switching operation stops input current flows ground through switching transistor. This generates heat inside proportion VCESAT IIN. Because short-circuit current during overload time restricted destroyed. Therefore, avoid overloading and/or short-circuiting output.
References
Semiconductor Technical Data Revision Series/Switching Regulator With Variable Output TL499A (SPRS039)
Designing Switching Voltage Regulators With TL499A
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