LT®3502/LT3502A current mode step-down DC/DC converters with internal

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LT®3502/LT3502A current mode step-down DC/DC converters with internal

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LT3502/LT3502A 1.1MHz/2.2MHz, 500mA Step-Down Regulators MS10 DESCRIPTION
LT®3502/LT3502A current mode step-down DC/DC converters with internal 500mA power switch, tiny 8-lead 10-lead MS10 packages. wide input voltage range makes LT3502/LT3502A suitable regulating power from wide variety sources, including industrial supplies automotive batteries. high operating frequency allows tiny, cost inductors capacitors, resulting very small solution. Constant frequency above band avoids interfering with radio reception, making LT3502A particularly suitable automotive applications. Cycle-by-cycle current limit frequency foldback provide protection against shorted outputs. Soft-start frequency foldback eliminates input current surge during start-up. current sense provides further protection fault conditions. internal boost diode reduces component count.
LTC, LTM, Linear Technology Linear logo registered trademarks Linear Technology Corporation. other trademarks property their respective owners.
Input Voltage Range 500mA Output Current Switching Frequency: 2.2MHz (LT3502A), 1.1MHz (LT3502) 800mV Feedback Voltage Short-Circuit Robust Soft-Start Shutdown Current: Internally Compensated Internal Boost Diode Thermally Enhanced 8-Lead 10-Lead MS10 Package
APPLICATIONS
Automotive Systems Battery-Powered Equipment Wall Transformer Regulation Distributed Supply Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
4.7V LT3502A SHDN 31.6k BOOST EFFICIENCY 0.1F 6.8H VOUT 3.3V 500mA 5VOUT
3502 TA01a
LT3502A 12VIN Efficiency
3.3VOUT
LOAD CURRENT
3502 TA01b
3502fd
LT3502/LT3502A ABSOLUTE MAXIMUM RATINGS
(Note
Input Voltage (VIN) .40V BOOST Voltage .50V BOOST Above Pin.7V Voltage SHDN Voltage .40V
Voltage Operating Junction Temperature Range (Note LT3502AE, LT3502E -40°C 125°C LT3502AI, LT3502I -40°C 125°C Storage Temperature Range -65°C 150°C
CONFIGURATION
VIEW SHDN BOOST BOOST VIEW SHDN
PACKAGE 8-LEAD (2mm 2mm) PLASTIC 102°C/W EXPOSED (PIN GND, MUST SOLDERED
PACKAGE 10-LEAD PLASTIC MSOP 110°C/W
ORDER INFORMATION
LEAD FREE FINISH LT3502EDC#PBF LT3502IDC#PBF LT3502AEDC#PBF LT3502AIDC#PBF LT3502EMS#PBF LT3502IMS#PBF LT3502AEMS#PBF LT3502AIMS#PBF TAPE REEL LT3502EDC#TRPBF LT3502IDC#TRPBF LT3502AEDC#TRPBF LT3502AIDC#TRPBF LT3502EMS#TRPBF LT3502IMS#TRPBF LT3502AEMS#TRPBF LT3502AIMS#TRPBF PART MARKING* LCLV LCLV LCLT LCLT LTDTR LTDTR LTDTS LTDTS PACKAGE DESCRIPTION 8-Lead Plastic 8-Lead Plastic 8-Lead Plastic 8-Lead Plastic 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP TEMPERATURE RANGE -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C
Consult Marketing parts specified with wider operating temperature ranges. *The temperature grade identified label shipping container. Consult Marketing information non-standard lead based finish parts. more information lead free part marking, http://www.linear.com/leadfree/ more information tape reel specifications,
3502fd
LT3502/LT3502A ELECTRICAL CHARACTERISTICS
PARAMETER Undervoltage Lockout Quiescent Current Shutdown Quiescent Current Feedback Voltage VSHDN Switching MS10 MS10 (Note 500mA (LT3502A) 500mA (LT3502A) 500mA (LT3502) 500mA (LT3502) 100mA Load (LT3502A) 100mA Load (LT3502) 500mA (Note (Note (Note 500mA 500mA IOUT 100mA VSHDN VSHDN 0.75
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 10V, VSHDN VBOOST 15V.
CONDITIONS 0.785 0.79 0.780 0.786 0.005
0.813 0.81 0.816 0.813
UNITS
Reference Voltage Line Regulation Bias Current Switching Frequency
2.25 2.25
Maximum Duty Cycle Switch VCESAT Switch Current Limit Switch Active Current BOOST Current Minimum BOOST Voltage Above Switch BOOST Schottky Forward Drop Current Stop SHDN Bias Current SHDN Input Voltage High SHDN Input Voltage
Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note LT3502EDC LT3502AEDC guaranteed meet performance specifications from 125°C junction temperature range. Specifications over -40°C 125°C operating junction temperature range assured design, characterization correlation
with statistical process controls. LT3502IDC LT3502AIDC guaranteed over 40°C 125°C operating junction temperature range. Note Current limit guaranteed design and/or correlation static test. Slope compensation reduces current limit higher duty cycle. Note Current flows into pin. Note Current flows pin.
3502fd
LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A 3.3VOUT Efficiency
EFFICIENCY LOAD CURRENT
3502
25°C unless otherwise noted)
LT3502A 5VOUT Efficiency
12VIN 24VIN EFFICIENCY LOAD CURRENT
3502
LT3502 3.3VOUT Efficiency
5VIN
12VIN
EFFICIENCY
24VIN
24VIN 12VIN
LOAD CURRENT
3502
LT3502 5VOUT Efficiency
EFFICIENCY LOAD CURRENT
3502
LT3502A Maximum Load Current VOUT 3.3V, 6.8H
TYPICAL LOAD CURRENT MINIMUM LOAD CURRENT
3502
LT3502A Maximum Load Current VOUT
TYPICAL
3502
12VIN 24VIN
MINIMUM
LT3502 Maximum Load Current VOUT 3.3V,
LOAD CURRENT
3502
LT3502 Maximum Load Current VOUT
TYPICAL LOAD CURRENT
3502
Switch Voltage Drop
(mV) 25°C 125°C
TYPICAL MINIMUM
MINIMUM
-40°C
3502
SWITCH CURRENT
3502fd
LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
UVLO
FREQUENCY (MHz) SWITCH CURRENT LIMIT LT3502A
25°C unless otherwise noted)
Switching Frequency
TEMPERATURE (°C)
3502
Soft-Start (SHDN)
LT3502
-0.1 TEMPERATURE (°C)
3502
1000 1200 1400 1600 SHDN VOLTAGE (mV)
3502
SHDN Current
SHDN CURRENT CURRENT LIMIT SHDN VOLTAGE
Switch Current Limit
CURRENT LIMIT
Switch Current Limit
PEAK CURRENT LIMIT VALLEY CURRENT LIMIT
LT3502 DUTY CYCLE
3502
LT3502A
TEMPERATURE (°C)
3502
3502
LT3502A Maximum Full Frequency (VOUT 3.3V)
LOAD CURRENT 85°C 25°C
LT3502A Maximum Full Frequency (VOUT
85°C 25°C LOAD CURRENT
LT3502 Maximum Full Frequency (VOUT 3.3V)
25°C 85°C
LOAD CURRENT
3502
3502
3502
3502fd
LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A Typical Minimum Input Voltage (VOUT 3.3V)
0.001 0.01 LOAD CURRENT
3502
25°C unless otherwise noted) LT3502 Typical Minimum Input Voltage (VOUT 3.3V)
0.001
LT3502A Typical Minimum Input Voltage (VOUT
0.001
0.01 LOAD CURRENT
3502
0.01 LOAD CURRENT
3502
LT3502 Typical Minimum Input Voltage (VOUT
0.001 0.01 LOAD CURRENT
3502
Continuous Mode Waveform
5V/DIV 5V/DIV
Discontinuous Mode Waveform
200mA/DIV VOUT 20mV/DIV VOUT 3.3V 6.8H COUT IOUT 250mA 200ns/DIV
3502
200mA/DIV VOUT 20mV/DIV VOUT 3.3V 6.8H COUT IOUT 30mA 200ns/DIV
3502
3502fd
LT3502/LT3502A FUNCTIONS
(DFN/MS)
(Pin 1/Pin 10): supplies current LT3502/LT3502A's internal regulator internal power switch. This must locally bypassed. (Pin 2/Pin used provide current internal boost Schottky diode. (Pin 3/Pin LT3502/LT3502A regulate their feedback 0.8V. Connect feedback resistor divider this pin. output voltage according VOUT R1/R2). good value 10k. SHDN (Pin 4/Pin SHDN used LT3502 shutdown mode. ground shut down LT3502/LT3502A. more normal operation. shutdown feature used, this pin. SHDN also provides soft-start frequency foldback. soft-start feature, connect SHDN pin. SHDN voltage should higher than VIN.
(Pin 5/Pin Ground Pin. (Pin 6/Pin Connect catch diode (D1) anode this pin. This used provide frequency foldback extreme situations. BOOST (Pin 7/Pin BOOST used provide drive voltage, higher than input voltage, internal bipolar power switch. Connect boost capacitor from this Pin. (Pin 8/Pin output internal power switch. Connect this inductor, catch diode boost capacitor.
3502fd
BLOCK DIAGRAM
LT3502/LT3502A
UVLO
SLOPE COMP SHDN DRIVER
BOOST
VOUT
FREQUENCY FOLDBACK
0.8V
3502
3502fd
LT3502/LT3502A OPERATION
LT3502/LT3502A constant frequency, current mode step-down regulators. oscillator enables flip-flop, turning internal 500mA power switch amplifier comparator monitor current flowing between pins, turning switch when this current reaches level determined voltage error amplifier measures output voltage through external resistor divider tied servos node. error amplifier's output increases, more current delivered output; decreases, less current delivered. active clamp (not shown) node provides current limit. node also clamped voltage SHDN pin; soft-start implemented generating voltage ramp SHDN using external resistor capacitor. SHDN voltage during soft-start also reduces oscillator frequency avoid hitting current limit during start-up. internal regulator provides power control circuitry. This regulator includes undervoltage lockout prevent switching when less than ~3V. SHDN used place LT3502/LT3502A shutdown, disconnecting output reducing input current less than switch driver operates from either from BOOST pin. external capacitor internal diode used generate voltage BOOST that higher than input supply. This allows driver fully saturate internal bipolar power switch efficient operation. comparator monitors current flowing through catch diode reduces LT3502/ LT3502A's operating frequency when current exceeds 650mA valley current limit. This frequency foldback helps control output current fault conditions such shorted output with high input voltage. comparator works conjunction with switch peak current limit comparator determine maximum deliverable current LT3502/LT3502A. peak current limit comparator used normal current mode operations used turn switch. valley current comparator monitors catch diode current will delay switching until catch diode current below 650mA limit. Maximum deliverable current output therefore limited both switch peak current limit valley current limit.
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
Resistor Network output voltage programmed with resistor divider between output pin. Choose resistors according 0.8V should less avoid bias current errors. Reference designators refer Block Diagram. Input Voltage Range input voltage range LT3502/LT3502A applications depends output voltage absolute maximum ratings BOOST pins. minimum input voltage determined either LT3502/LT3502A's minimum operating voltage maximum duty cycle. duty cycle fraction time that internal switch determined input output voltages: VOUT where forward voltage drop catch diode (~0.4V) voltage drop internal switch (~0.45V maximum load). This leads minimum input voltage VIN(MIN) DCMAX with DCMAX 0.80 LT3502A 0.90 LT3502. maximum input voltage determined absolute maximum ratings BOOST pins. fixed frequency operation, maximum input voltage determined minimum duty cycle DCMIN: VIN(MAX) VOUT DCMIN Note that this restriction operating input voltage fixed frequency operation; circuit will tolerate transient inputs absolute maximum ratings BOOST pins. input voltage should limited operating range (40V) during overload conditions. Minimum On-Time LT3502/LT3502A will still regulate output input voltages that exceed VIN(MAX) 40V), however, output voltage ripple increases input voltage increased. input voltage increased, part required switch shorter periods time. Delays associated with turning power switch dictate minimum on-time part. minimum on-time LT3502/LT3502A 60ns (Figure
20V/DIV
500mA/DIV VOUT 100mV/DIV 1s/DIV 33V, VOUT 3.3V 6.8H, COUT 10F, IOUT 250mA
3502
Figure Continuous Mode Operation Near Minimum On-Time 60ns
When required on-time decreases below minimum on-time 60ns, instead switch pulse width becoming narrower accommodate lower duty cycle requirement, switch pulse width remains fixed 60ns. inductor current ramps value exceeding load current output ripple increases. part then remains until output voltage dips below programmed value before begins switching again (Figure Provided that load tolerate increased output voltage ripple that components have been properly selected, operation above VIN(MAX) safe will damage part.
3502fd
DCMIN 0.15 LT3502A 0.08 LT3502.
LT3502/LT3502A APPLICATIONS INFORMATION
20V/DIV 20V/DIV
500mA/DIV VOUT 100mV/DIV 1s/DIV 40V, VOUT 3.3V 6.8H, COUT 10F, IOUT 250mA
3502
500mA/DIV VOUT 100mV/DIV 1s/DIV 40V, VOUT 3.3V 6.8H, COUT 10F, IOUT 500mA
3502
Figure Pulse-Skipping Occurs when Required On-Time Below 60ns
Figure Pulse-Skipping with Large Load Current Will Limited Valley Current Limit. Notice Flat Inductor Valley Current Reduced Switching Frequency
input voltage increases, inductor current ramps quicker, number skipped pulses increases output voltage ripple increases. operation above VIN(MAX) only component requirement that components adequately rated operation intended voltage levels. Inductor current reach current limit when operating pulse-skipping mode with small valued inductors. this case, LT3502/LT3502A will periodically reduce frequency keep inductor valley current 650mA (Figure Peak inductor current therefore peak current plus minimum switch delay: VOUT 60ns part robust enough survive prolonged operation under these conditions long peak inductor current does exceed 1.2A. Inductor current saturation junction temperature further limit performance during this operating regime. 900mA
Table
VENDOR Sumida www.sumida.com
Inductor Selection Maximum Output Current good first choice inductor value 1.6(VOUT LT3502A 4.6(VOUT LT3502 where voltage drop catch diode (~0.4V) With this value there will subharmonic oscillation applications with greater duty cycle. inductor's current rating must greater than maximum load current saturation current should about higher. robust operation during fault conditions, saturation current should above 1.2A. keep efficiency high, series resistance (DCR) should less than 0.1. Table lists several vendors types that suitable. There several graphs Typical Performance Characteristics section this data sheet that show maximum load current function input voltage inductor value several popular output voltages. inductance result discontinuous mode operaINDUCTANCE RATE SIZE (mm)
3502fd
Toko Elektronik
www.toko.com www.we-online.com
PART SERIES CDRH4D28 CDRH5D28 CDRH8D28 A916CY D585LC WE-TPC(M) WE-PD2(M) WE-PD(S)
LT3502/LT3502A APPLICATIONS INFORMATION
tion, which okay, further reduces maximum load current. details maximum output current discontinuous mode operation, Linear Technology Application Note Catch Diode capacitance 500mA Schottky diode recommended catch diode, diode must have reverse voltage rating equal greater than maximum input voltage. Diodes Inc. SBR1U40LP Semi MBRM140, Diodes Inc. DFLS140 good choices catch diode. Input Capacitor Bypass input LT3502/LT3502A circuit with higher value ceramic capacitor type. types have poor performance over temperature applied voltage should used. ceramic adequate bypass LT3502/LT3502A will easily handle ripple current. However, input power source high impedance, there significant inductance long wires cables, additional bulk capacitance necessary. This provided with performance electrolytic capacitor. Step-down regulators draw current from input supply pulses with very fast rise fall times. input capacitor required reduce resulting voltage ripple LT3502/LT3502A force this very high frequency switching current into tight local loop, minimizing EMI. capacitor capable this task, only placed close LT3502/LT3502A catch diode (see Layout section). second precaution regarding ceramic input capacitor concerns maximum input voltage rating LT3502/LT3502A. ceramic input capacitor combined with trace cable inductance forms high quality (underdamped) tank circuit. LT3502/LT3502A circuit plugged into live supply, input voltage ring twice nominal value, possibly exceeding LT3502/LT3502A's voltage rating. This situation easily avoided; Plugging Safely section. COUT Output Capacitor output capacitor essential functions. Along with inductor, filters square wave generated LT3502/LT3502A produce output. this role determines output ripple impedance switching frequency important. second function store energy order satisfy transient loads stabilize LT3502/LT3502A's control loop. Ceramic capacitors have very equivalent series resistance (ESR) provide best ripple performance. good value COUT LT3502A VOUT LT3502 VOUT
where COUT type keep mind that ceramic capacitor biased with VOUT will have less than nominal capacitance. This choice will provide output ripple good transient response. Transient performance improved with high value capacitor, phase lead capacitor across feedback resistor, required full benefit (see Compensation section). small size, output capacitor chosen according COUT VOUT where COUT However, using output capacitor this small results increased loop crossover frequency increased sensitivity noise. High performance electrolytic capacitors used output capacitor. important, choose that intended switching regulators. should specified supplier should less. Such capacitor will larger than ceramic capacitor will have larger capacitance, because capacitor must large achieve ESR. Table lists several capacitor vendors.
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
Table
VENDOR Panasonic PHONE (714) 373-7366 www.panasonic.com PART SERIES Ceramic Polymer, Tantalum Ceramic, Tantalum Ceramic Polymer, Tantalum Ceramic Ceramic, Tantalum Ceramic COMMENTS Series T494,T495
Kemet Sanyo
(864) 963-6300 (408)794-9714
www.kemet.com www.sanyovideo.com
POSCAP
Murata Taiyo Yuden
(404) 436-1300
www.murata.com www.avxcorp.com www.taiyo-yuden.com
Series
(864) 963-6300
Figure shows transient response LT3502A with several output capacitor choices. output 3.3V. load current stepped from 150mA 400mA back 150mA, oscilloscope traces show output voltage. upper photo shows recommended value. second photo shows improved response (less voltage drop) resulting from larger output capacitor phase lead capacitor. last photo shows response high performance electrolytic capacitor. Transient performance improved large output capacitance. BOOST Considerations Capacitor internal boost diode used generate boost voltage that higher than input voltage. most cases 0.1F capacitor will work well. Figure shows ways arrange boost circuit. BOOST must least 2.2V above best efficiency. outputs above, standard circuit (Figure best. outputs less than above 2.5V, place discrete Schottky diode (such BAT54) parallel with internal diode reduce following equations used calculate minimize boost capacitance 0.012/(VBD VCATCH 2.2) LT3502A 0.030/(VBD VCATCH 2.2) LT3502 forward drop boost diode, VCATCH forward drop catch diode (D1). lower output voltages tied external voltage source with adequate local bypassing
(Figure 5b). above equations still apply calculating optimal boost capacitor chosen voltage. absence voltage during start-up will increase minimum voltage start reduce efficiency. must also sure that maximum voltage rating BOOST exceeded. minimum operating voltage LT3502/LT3502A application limited undervoltage lockout (3V) maximum duty cycle outlined above. proper start-up, minimum input voltage also limited boost circuit. input voltage ramped slowly, LT3502/LT3502A turned with SHDN when output already regulation, then boost capacitor fully charged. Because boost capacitor charged with energy stored inductor, circuit will rely some minimum load current boost circuit running properly. This minimum load will depend input output voltages, arrangement boost circuit. minimum load generally goes zero once circuit started. Figure shows plots minimum load start function input voltage. many cases discharged output capacitor will present load switcher which will allow start. plots show worst-case situation where ramping very slowly. light loads, inductor current becomes discontinuous effective duty cycle very high. This reduces minimum input voltage approximately 400mV above VOUT. higher load currents, inductor current continuous duty cycle limited maximum duty cycle LT3502/LT3502A, requiring higher input voltage maintain regulation.
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
VOUT 32.4k 0.2A/DIV VOUT 0.1V/DIV COUPLED
10s/DIV
3502 F04a
VOUT 32.4k 50pF 0.2A/DIV VOUT 0.1V/DIV COUPLED
10s/DIV
3502 F04b
VOUT 32.4k
100F SANYO 4TPB100M
0.2A/DIV VOUT 0.1V/DIV COUPLED
10s/DIV
3502 F04c
Figure Transient Load Response LT3502A with Different Output Capacitors Load Current Stepped from 150mA 400mA. 12V, VOUT 3.3V, 6.8H
BOOST LT3502 VOUT BOOST LT3502 VOUT
VBOOST VOUT VBOOST VOUT
3502 F05a
VBOOST VBOOST
3502 F05b
(5a)
(5b)
Figure
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
START 0.001 0.01 LOAD CURRENT
3502
START
0.001
0.01 LOAD CURRENT
3502
(6a) LT3502A Typical Minimum Input Voltage, VOUT 3.3V
(6b) LT3502A Typical Minimum Input Voltage, VOUT
START
0.001
START
0.01 LOAD CURRENT
3502
0.001
0.01 LOAD CURRENT
3502
(6c) LT3502 Typical Minimum Input Voltage, VOUT 3.3V Figure
(6d) LT3502 Typical Minimum Input Voltage, VOUT
Soft-Start SHDN used soft start LT3502/LT3502A, reducing maximum input current during start-up. SHDN driven through external filter create voltage ramp this pin. Figure shows start-up waveforms with without soft-start circuit. choosing large time constant, peak start-up current reduced current that required regulate output, with overshoot. Choose value resistor that supply when SHDN reaches
Short Reverse Protection inductor chosen that won't saturate excessively, LT3502/LT3502A will tolerate shorted output. When operating short-circuit condition, LT3502/LT3502A will reduce their frequency until valley current 650mA (Figure 8a). There another situation consider systems where output will held high when input LT3502/LT3502A absent. This occur battery charging applications battery backup systems where battery some other supply diode OR-ed with LT3502/LT3502A's output. allowed float SHDN held high (either logic signal
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
10V/DIV SHDN
3502 F07a
500mA/DIV
VOUT 2V/DIV VOUT 3.3V 6.8H COUT SHDN 0.1F
3502 F07b
5s/DIV
10V/DIV
500mA/DIV VOUT 2V/DIV VOUT 3.3V 6.8H COUT 50s/DIV
3502
Figure Soft-Start LT3502A, Resistor Capacitor SHDN
10V/DIV
BOOST LT3502A VOUT
500mA/DIV
SHDN VOUT 6.8H COUT 2s/DIV
3502 F08a
3502 F08b
Figure LT3502A Reduces Frequency Below 500kHz Protect Against Shorted Output with Input
Figure Diode Prevents Shorted Input from Discharging Backup Battery Tied Output; Also Protects Circuit from Reversed Input. LT3502/LT3502A Runs Only When Input Present
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
because tied VIN), then LT3502/LT3502A's internal circuitry will pull quiescent current through pin. This fine your system tolerate this state. ground SHDN pin, current will drop essentially zero. However, grounded while output held high, then parasitic diodes inside LT3502/LT3502A pull large currents from output through pin. Figure shows circuit that will only when input voltage present that protects against shorted reversed input. Plugging Safely small size, robustness impedance ceramic capacitors make them attractive option input bypass capacitor LT3502/LT3502A circuits. However, these capacitors cause problems LT3502/LT3502A
CLOSING SWITCH SIMULATES PLUG LT3502
plugged into live supply (see Linear Technology Application Note complete discussion). loss ceramic capacitor combined with stray inductance series with power source forms underdamped tank circuit, voltage LT3502/LT3502A ring twice nominal input voltage, possibly exceeding LT3502/LT3502A's rating damaging part. input supply poorly controlled user will plugging LT3502/LT3502A into energized supply, input network should designed prevent this overshoot. Figure shows waveforms that result when LT3502/LT3502A circuit connected supply through feet 24-gauge twisted pair. first plot response with 2.2F ceramic capacitor input. input voltage rings high input current peaks 20A. method damping tank circuit another capacitor with series resistor
DANGER! 20V/DIV RINGING EXCEED ABSOLUTE MAXIMUM RATING LT3502
2.2F
IMPEDANCE ENERGIZED SUPPLY
STRAY INDUCTANCE FEET METERS) TWISTED PAIR
5A/DIV 20s/DIV
(9a)
LT3502 20V/DIV
AI.EI.
2.2F
5A/DIV
(9b)
LT3502 20V/DIV
20s/DIV
0.1F 2.2F
5A/DIV
(9c)
20s/DIV
3502
Figure Well Chosen Input Network Prevents Input Voltage Overshoot Ensures Reliable Operation When LT3502 Connected Live Supply
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
circuit. Figure aluminum electrolytic capacitor been added. This capacitor's high equivalent series resistance damps circuit eliminates voltage overshoot. extra capacitor improves frequency ripple filtering slightly improve efficiency circuit, though likely largest component circuit. alternative solution shown Figure resistor added series with input eliminate voltage overshoot also reduces peak input current). 0.1F capacitor improves high frequency filtering. This solution smaller less expensive than electrolytic capacitor. high input voltages impact efficiency minor, reducing efficiency less than half percent output full load operating from 24V. Frequency Compensation LT3502/LT3502A current mode control regulate output. This simplifies loop compensation. particular, LT3502/LT3502A does require output capacitor stability allowing ceramic capacitors achieve output ripple small circuit size. Figure shows equivalent circuit LT3502/ LT3502A control loop. error transconductance amplifier with finite output impedance. power section, consisting modulator, power switch inductor, modeled transconductance amplifier generating output current proportional voltage node. Note that output capacitor integrates this current,
LT3502 0.5V CURRENT MODE POWER STAGE 1A/V
that capacitor node (CC) integrates error amplifier output current, resulting poles loop. provides zero. With recommended output capacitor, loop crossover occurs above RCCC zero. This simple model works well long value inductor high loop crossover frequency much lower than switching frequency. With larger ceramic capacitor (very ESR), crossover lower phase lead capacitor (CPL) across feedback divider improve phase margin transient response. Large electrolytic capacitors have large enough create additional zero, phase lead necessary. output capacitor different than recommended capacitor, stability should checked across operating conditions, including load current, input voltage temperature. LT1375 data sheet contains more thorough discussion loop compensation describes test stability using transient load. Layout proper operation minimum EMI, care must taken during printed circuit board layout. Figure shows recommended component placement with trace, ground plane locations. Note that large, switched currents flow LT3502/LT3502A's pins, catch diode (D1) input capacitor (C2).
VOUT
150k 70pF
ERROR AMPLIFIER
Figure Model Loop Response
100A/V
800mV
SHDN
3502
3502
Figure
3502fd
LT3502/LT3502A APPLICATIONS INFORMATION
loop formed these components should small possible tied system ground only place. These components, along with inductor output capacitor, should placed same side circuit board, their connections should made that layer. Place local, unbroken ground plane below these components, this ground plane system ground location, ideally ground terminal output capacitor BOOST nodes should small possible. Finally, keep node small that ground ground traces will shield from BOOST nodes. Include vias near exposed LT3502/LT3502A help remove heat from LT3502/LT3502A ground plane. High Temperature Considerations temperature LT3502/LT3502A must lower than maximum rating 125°C. This generally concern unless ambient temperature above 85°C. higher temperatures, care should taken layout circuit ensure good heat sinking LT3502/LT3502A. maximum load current should derated ambient temperature approaches 125°C. temperature calculated multiplying LT3502/LT3502A power dissipation thermal resistance from junction ambient. Power dissipation within LT3502/LT3502A estimated calculating total power loss from efficiency measurement subtracting catch diode loss. Thermal resistance depends layout circuit board, 102°C/W typical (2mm 2mm) MS10 packages respectively. Outputs Greater Than Note that outputs above input voltage range will limited maximum rating BOOST pin. input output voltages cannot exceed BOOST pin's rating. circuit (Figure shows overcome this limitation using additional Zener diode. Other Linear Technology Publications Application Notes AN19, AN35 AN44 contain more detailed descriptions design information Buck regulators other switching regulators. LT1376 data sheet more extensive discussion output ripple, loop compensation stability testing. Design Note shows generate bipolar output supply using buck regulator.
1N4148 OTHER SIMILAR DIODES 0.1F
LT3502A 180k
3502
BOOST 0.1F
22pF
VOUT 500mA
SHDN
Figure Step-Down Converter
3502fd
LT3502/LT3502A TYPICAL APPLICATIONS
0.8V Step-Down Converter
0.1F BOOST LT3502A SHDN JMK212BJ476MG HMK212BJ104MG LQH43CN3R3M03
3502 TA02a
VOUT 0.8V 500mA
0.1F BOOST 0.1F LT3502 SHDN JMK316BJ107ML LQH43CN100K03 100F
3502 TA02b
0.1F 3.3H
VOUT 0.8V 500mA
1.8V Step-Down Converter
0.1F BOOST LT3502A SHDN
3502 TA03a
0.1F BOOST 0.1F LT3502 12.5k
3502 TA03b
0.1F 4.7H 12.5k
VOUT 1.8V 500mA
VOUT 1.8V 500mA
SHDN
JMK212BJ226MG LQH43CN4R7M03
JMK212BJ476MG LQH55DN150M03
3502fd
LT3502/LT3502A TYPICAL APPLICATIONS
2.5V Step-Down Converter
3.5V BOOST LT3502A SHDN
3502 TA04a
0.1F
0.1F BOOST 0.1F LT3502 21.3k
3502 TA04b
0.1F 6.8H 21.3k
3.5V VOUT 2.5V 500mA
VOUT 2.5V 500mA
SHDN
JMK212BJ226MG LQH43DN6R8M03
JMK212BJ226MG LQH55DN150M03
3.3V Step-Down Converter
4.7V
LT3502A SHDN
3502 TA05a
BOOST
0.1F 6.8H 31.6k
4.5V VOUT 3.3V 500mA
LT3502 SHDN
3502 TA05b
BOOST 0.1F 31.6k
VOUT 3.3V 500mA
LMK316BJ106ML-BR LQH43CN6R8M03
JMK212BJ226MG LQH55DN150M03
3502fd
LT3502/LT3502A PACKAGE DESCRIPTION
Package 8-Lead Plastic (2mm 2mm)
(Reference 05-08-1719
0.70 0.05 2.55 0.05 1.15 0.05 0.64 0.05 SIDES)
PACKAGE OUTLINE
0.25 0.45 1.37 0.05 SIDES)
0.05
RECOMMENDED SOLDER PITCH DIMENSIONS APPLY SOLDER MASK AREAS THAT SOLDERED 0.05 2.00 0.10 SIDES)
0.115
0.40 0.10
MARK (SEE NOTE
0.64 0.10 SIDES)
NOTCH 0.20 0.25 CHAMFER
(DC8) 0106
0.200 0.75 0.05 1.37 0.10 SIDES) 0.00 0.05
0.23 0.45
0.05
BOTTOM VIEW-EXPOSED
NOTE: DRAWING JEDEC PACKAGE OUTLINE DRAWING SCALE DIMENSIONS MILLIMETERS DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.15mm SIDE EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
3502fd
LT3502/LT3502A PACKAGE DESCRIPTION
Package 10-Lead Plastic MSOP
(Reference 05-08-1661
0.889 0.127 (.035 .005)
5.23 (.206)
3.20 3.45 (.126 .136) 3.00 0.102 (.118 .004) (NOTE
0.50 0.305 0.038 (.0197) (.0120 .0015) RECOMMENDED SOLDER LAYOUT
0.497 0.076 (.0196 .003)
0.254 (.010) GAUGE PLANE
DETAIL
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE
0.53 0.152 (.021 .006) DETAIL 0.18 (.007) SEATING PLANE 0.17 0.27 (.007 .011) 0.1016 0.0508 (.004 .002)
MSOP (MS) 0307
1.10 (.043)
0.86 (.034)
0.50 (.0197) NOTE: DIMENSIONS MILLIMETER/(INCH) DRAWING SCALE DIMENSION DOES INCLUDE MOLD FLASH, PROTRUSIONS GATE BURRS. MOLD FLASH, PROTRUSIONS GATE BURRS SHALL EXCEED 0.152mm (.006") SIDE DIMENSION DOES INCLUDE INTERLEAD FLASH PROTRUSIONS. INTERLEAD FLASH PROTRUSIONS SHALL EXCEED 0.152mm (.006") SIDE LEAD COPLANARITY (BOTTOM LEADS AFTER FORMING) SHALL 0.102mm (.004")
3502fd
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
LT3502/LT3502A TYPICAL APPLICATION
Step-Down Converter
6.7V LT3502A SHDN
3502 TA06a
BOOST 0.1F 52.3k
6.4V VOUT 500mA
LT3502 SHDN
3502 TA06b
BOOST 0.1F 52.3k
VOUT 500mA
LMK316BJ106ML-BR LQH43CN100K03
LMK316BJ106ML-BR LQH43CN100K03
RELATED PARTS
PART NUMBER LT1766 LT1933 LT1936 LT1940 LT1976/ LT1977 3407/ LTC3407-2 LT3434/ LT3435 LT3437 LT3493 LT3501 LT3503 LT3505 LT3506/ LT3506A LT3508 LT3510 LTC3548 DESCRIPTION 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter 500mA (IOUT), 500kHz, Step-Down Switching Regulator SOT-23 36V, 1.4A (IOUT), 500kHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down DC/DC Converter 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode® Operation Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous Step-DownDC/DC Converters 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode Operation 60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with Burst Mode Operation 36V, 1.4A (IOUT), 750kHz, High Efficiency Step-Down DC/DC Converter Dual 25V, (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter 20V, (IOUT), 2.2MHz, High Efficiency Step-Down DC/DC Converter 36V, 1.2A (IOUT), 3MHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Efficiency StepDown DC/DC Converters Dual 36V, 1.4A (IOUT), 2.5MHz, High Efficiency Step-Down DC/DC Converter Dual 25V, (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter Dual 400mA 800mA, 2.25MHz Synchronous Step-Down DC/DC Converter COMMENTS VIN: 5.5V 60V, VOUT(MIN) 1.2V, 2.5mA, 25A, TSSOP16/TSSOP16E Packages VIN: 3.6V 36V, VOUT(MIN) 1.2V, 1.6mA, ThinSOTPackage VIN: 3.6V 36V, VOUT(MIN) 1.2V, 1.9mA, MS8E Package VIN: 3.6V 25V, VOUT(MIN) 1.20V, 3.8mA, 30A, TSSOP16E Package VIN: 3.3V 60V, VOUT(MIN) 1.20V, 100A, TSSOP16E Package VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 40A, <1A, DFN, MS10E Package VIN: 3.3V 60V, VOUT(MIN) 1.20V, 100A, TSSOP16E Package VIN: 3.3V 60V, VOUT(MIN) 1.25V, 100A, Package VIN: 3.6V 36V, VOUT(MIN) 0.8V, 1.9mA, Package VIN: 3.3V 25V, VOUT(MIN) 0.8V, 3.7mA, 10A, TSSOP20E Package VIN: 3.6V 20V, VOUT(MIN) 0.78V, 1.9mA, Package VIN: 3.6V 36V, VOUT(MIN) 0.78V, 2mA, DFN, MS8E Packages VIN: 3.6V 25V, VOUT(MIN) 0.8V, 3.8mA, 30A, Package VIN: 3.6V 36V, VOUT(MIN) 0.8V, 4.3mA, QFN, TSSOP16E Packages VIN: 3.3V 25V, VOUT(MIN) 0.8V, 3.7mA, 10A, TSSOP20E Package VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 40A, DFN, MS10E Packages
3502fd
Burst Mode registered trademark Linear Technology Corporation. ThinSOT trademark Linear Technology Corporation.
Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
0809 PRINTED
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2007

LT®3502/LT3502A current mode step-down DC/DC converters with internal

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