LTC1143 dual step-down switching regulator controller featuring automa

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LTC1143 dual step-down switching regulator controller featuring automa

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LTC1143 Dual High Efficiency Step-Down Switching Regulator Controller
LTC1143 dual step-down switching regulator controller featuring automatic Burst Modeoperation maintain high efficiencies output currents. This device composed separate regulator blocks, each driving external power MOSFET switching frequencies exceeding 400kHz using constant off-time current mode architecture providing constant ripple current inductor. operating current level both regulators userprogrammable external current sense resistor. Wide input supply range allows operation from (16V maximum). Constant off-time architecture provides dropout regulation limited only RDS(ON) external MOSFET resistance inductor current sense resistor. LTC1143 ideal applications requiring dual output voltages with high conversion efficiencies over wide load current range small amount board space.
Burst Mode trademark Linear Technology Corporation.
Dual Outputs: 3.3V 5.0V Very High Efficiency: Over Possible Current Mode Operation Excellent Line Load Transient Response High Efficiency Maintained Over Decades Output Current Standby Current Light Loads: 160µA/Output Independent Micropower Shutdown: 40µA Wide Range: Very Dropout Operation: 100% Duty Cycle Available Narrow 16-Pin SOIC Package
APPLICATIONS
Notebook Palmtop Computers Battery-Operated Digital Devices Portable Instruments Power Distribution Systems
TYPICAL APPLICATION
CIN3 22µF 0.22µF P-CH Si9430DY 1000pF SENSE VIN3 P-DRIVE SENSE
5.2V
NORMAL >1.5V SHUTDOWN SHUTDOWN SHUTDOWN
VIN5 P-DRIVE SENSE
VOUT3 3.3V/2A
RSENSE3 0.05
50µH
LTC1143 SENSE
COUT3 220µF
MRD330 GND3 560pF ITH3 3300pF ITH5 3300pF 390pF GND5
RSENSE3, RSENSE5: SL-1/2-CI-0R050J
COILTRONICS CTX50-2-MP COILTRONICS CTX50-2-MP
NOTE: COMPONENTS OPTIMIZED HIGHEST EFFICIENCY, MINIMUM BOARD SPACE.
Figure High Efficiency Dual 3.3V/5V
0.22µF P-CH Si9430DY 50µH
CIN5 22µF
RSENSE5 0.05
VOUT5 5V/2A
1000pF
MBRD330
COUT5 220µF
1143
LTC1143
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage (Pins 5,13) -0.3V Continuous Output Current (Pins 4,12) 50mA Sense Voltages (Pins 16). -0.3V Operating Ambient Temperature Range 70°C Extended Commercial Temperature Range. -40°C 85°C Junction Temperature (Note 125°C Storage Temperature Range -65°C 150°C Lead Temperature (Soldering, sec). 300°C
PACKAGE/ORDER INFORMATION
VIEW SENSE SHUTDOWN GND3 P-DRIVE VIN5 ITH5 SENSE-5
SENSE-3 ITH3 VIN3 P-DRIVE GND5 SHUTDOWN SENSE+5
ORDER PART NUMBER LTC1143CS
PACKAGE 16-LEAD PLASTIC SOIC
TJMAX 125°C, 95°C/W
Consult factory Industrial Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VOUT PARAMETER Regulated Output Voltage 3.3V Output Output Output Voltage Line Regulation Output Voltage Load Regulation 3.3V Output Output Output Ripple (Burst Mode) Input Supply Current (Note Normal Mode Sleep Mode Shutdown Current-Sense Threshold Voltage 3.3V Section Section Shutdown Threshold Shutdown Input Current Discharge Current Off-Time (Note Driver Output Transition Times CONDITIONS
25°C, VIN3 VIN5 10V, unless otherwise noted.
3.33 5.05
3.43 5.20
UNITS mVP-P
VIN3, VIN5 ILOAD 700mA ILOAD 700mA VIN3, VIN5 12V, ILOAD 50mA Figure Circuit ILOAD 2.0A ILOAD 2.0A ILOAD VIN3, VIN5 VIN3 12V, VIN5 2.1V, VIN3, VIN5 VOUT 100mV (Forced) VOUT 100mV (Forced) VOUT 100mV (Forced) VOUT 100mV (Forced) VSHUTDOWN VIN3, VIN5 VOUT Regulation, VSENSE- VOUT VOUT 390pF, ILOAD 700mA 3000pF (Pins 12),
3.23 4.90
VOUT VOUT
VOUT
tOFF
LTC1143 ELECTRICAL CHARACTERISTICS
SYMBOL VOUT PARAMETER Regulated Output Voltage 3.3V Output Output Input Supply Current (Note Normal Mode Sleep Mode Shutdown Current Sense Threshold Voltage 3.3V Section Section Shutdown Threshold Off-Time (Note 390pF, ILOAD 700mA CONDITIONS VIN3, VIN5 ILOAD 700mA ILOAD 700mA VIN3, VIN5 VIN3, VIN5 2.1V, VIN3, VIN5 VOUT 100mV (Forced) VOUT 100mV (Forced) VOUT 100mV (Forced) VOUT 100mV (Forced)
-40°C 85°C (Note VIN3 VIN5 10V, unless otherwise noted.
3.17 4.85 3.33 5.05 UNITS
tOFF
0.55
denotes specifications which apply over operating temperature range. Note calculated from ambient temperature power dissipation according following formula: LTC1143CS: 120°C/W) Note This supply current regulator block. Total supply current currents. Dynamic supply current
higher gate charge being delivered switching frequency. Applications Information. Note applications where RSENSE placed ground potential, off-time increases approximately 40%. Note LTC1143 tested quality assurance sampled -40°C 85°C. These specifications guaranteed design and/or correlation.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Efficiency
EFFICIENCY
1000
LTC1143
EFFICIENCY
EFFICIENCY
LOAD CURRENT (mA)
3.3V Output Efficiency
1000
LTC1143
Efficiency Input Voltage
INPUT VOLTAGE
LTC1143
FIGURE CIRCUIT
ILOAD
ILOAD 100mA
LOAD CURRENT (mA)
LTC1143 TYPICAL PERFORMANCE CHARACTERISTICS
3.3V Efficiency Input Voltage
EFFICIENCY
FIGURE CIRCUIT VOUT 3.3V
INPUT VOLTAGE
LTC1143
VOUT (mV)
VOUT (mV)
ILOAD ILOAD 100mA
Supply Current
INCLUDING GATE CHARGE CURRENT ACTIVE MODE PINS
NORMALIZED FREQUENCY
SUPPLY CURRENT (mA)
SUPPLY CURRENT (µA)
REGULATOR BLOCK
SLEEP MODE INPUT VOLTAGE
Gate Charge Supply Current
GATE CHARGE CURRENT (mA)
100nC
SENSE VOLTAGE (mV)
OFF-TIME (µs)
29nC OPERATING FREQUENCY (kHz)
LTC1143
LTC1143
Line Regulation
INPUT VOLTAGE
LTC1143
Load Regulation
FIGURE CIRCUIT RSENSE 0.05
FIGURE CIRCUIT ILOAD
-100
VOUT VOUT 3.3V LOAD CURRENT
LTC1143
Supply Current Shutdown
INPUT VOLTAGE
Operating Frequency VOUT
VOUT 25°C 70°C
REGULATOR BLOCK PINS VSHUTDOWN
(VIN VOUT) VOLTAGE
LTC1143
LTC1143
Off-Time VOUT
VOUT 3.3V OUTPUT VOLTAGE
LTC1143
Current Sense Threshold Voltage
VSENSE VOUT
MAXIMUM THRESHOLD
VOUT
MINIMUM THRESHOLD
TEMPERATURE (°C)
LTC1143
LTC1143
FUNCTIONS
SENSE+3 (Pin Input 3.3V Section Current Comparator. built offset between pins conjunction with RSENSE sets current trip threshold 3.3V section. SHUTDOWN (Pin When grounded, 3.3V section operates normally. Pulling high holds MOSFET puts 3.3V section micropower shutdown mode. Requires CMOS logic level signal with 1µs. "float" GND3 (Pin 3.3V Section Ground. independent ground lines must routed separately from other grounds terminal 3.3V section output capacitor, cathode Schottky diode terminal CIN3 (See Figures P-DRIVE (Pin High Current Drive P-Channel MOSFET, 3.3V Section. Voltage swing this from VIN3 ground. VIN5 (Pin Supply Pin, Section. Must closely decoupled power ground (Pin External capacitor from ground sets operating frequency section. (The actual frequency also dependent upon input voltage.) ITH5 (Pin Gain Amplifier Decoupling Point, Section. section current comparator threshold increases with voltage. SENSE- (Pin Connects internal resistive divider which sets output voltage section. also input current comparator section. SENSE+ (Pin Input Section Current Comparator. built-in offset between pins conjunction with RSENSE sets current trip threshold section. SHUTDOWN (Pin 10): When grounded, section operates normally. Pulling high holds section MOSFET puts section micropower shutdown mode. Requires CMOS logic level signal with 1µs. "float" GND5 (Pin 11): Section Ground. independent ground lines must routed separately from other grounds terminal section output capacitor, cathode Schottky diode terminal CIN5 (See Figures P-DRIVE (Pin 12): High Current Drive P-Channel MOSFET, Section. Voltage swing this from VIN5 ground. VIN3 (Pin 13): Supply Pin, 3.3V Section. Must closely decoupled 3.3V power ground (Pin 14): External capacitor from ground sets operating frequency 3.3V section. (The actual frequency also dependent upon input voltage.) ITH3 (Pin 15): Gain Amplifier Decoupling Point, 3.3V Section. 3.3V section current comparator threshold increases with voltage. SENSE (Pin 16): Connects internal resistive divider which sets output voltage 3.3V section. also input current comparator 3.3V section.
LTC1143
FUNCTIONAL DIAGRA
SLEEP
VTH1
VTH2
14(6)
OFF-TIME CONTROL
OPERATION
Refer Functional Diagram Figure
LTC1143 consists individual regulator blocks each using current mode, constant off-time architectures switch external power MOSFET. regulators internally provide output voltages 3.3V Operating frequency individually each section external capacitors timing capacitor pins output voltage sensed internal voltage divider connected Sense (8). voltage comparator gain block compare divided output voltage with reference voltage 1.25V. optimize efficiency, LTC1143 automatically switches between modes operation, burst continuous. voltage comparator primary control element when device Burst Mode operation, while gain block controls output voltage continuous mode. During switch "ON" cycle continuous mode, current comparator monitors voltage between pins connected across external shunt series with inductor. When voltage across shunt reaches threshold value, P-drive output switched VIN, turning P-channel MOSFET. timing capacitor connected allowed discharge rate determined off-time controller. discharge
Only regulator block shown. numbers 3.3V (5V) sections.
13(5) SENSE 1(9) 3(11) GROUND SENSE 16(8)
4(12)
P-DRIVE
25mV 150mV
15(7)
1.25V 100k
SENSE
SHUTDOWN 2(10) REFERENCE
1143
current made proportional output voltage [measured (8)] model inductor current, which decays rate which also proportional output voltage. When voltage timing capacitor discharged past VTH1, comparator trips, setting flip-flop. This causes P-drive output turning P-channel MOSFET back cycle then repeats. load current increases, output voltage decreases slightly. This causes output gain stage [pin (7)] increase current comparator threshold, thus tracking load current. sequence events Burst Mode operation very similar continuous operation with cycle interrupted voltage comparator. When output voltage above desired regulated value, P-channel MOSFET held comparator timing capacitor continues discharge below VTH1. When timing capacitor discharges past VTH2, voltage comparator trips, causing internal sleep line low. circuit enters sleep mode with power MOSFET turned off. sleep mode majority circuitry
LTC1143
OPERATION
turned off, dropping quiescent current from 1.6mA 160µA (for regulator block). load current being supplied from output capacitor. When output voltage dropped amount hysteresis comparator P-channel MOSFET again turned process repeats. avoid operation current loop interfering with Burst Mode operation, built-in offset (VOS) incorporated gain stage. This prevents current compara-
APPLICATIONS INFORMATION
basic LTC1143 application circuit shown Figure External component selection driven load requirement begins with selection RSENSE. Once RSENSE known, chosen. Next, power MOSFET selected. Finally, COUT selected loop compensated. Since 3.3V sections identical, process component selection same both sections. circuit shown Figure configured operation input voltage 16V. RSENSE Selection Output Current RSENSE chosen based required output current. LTC1143 current comparators have threshold range which extends from minimum 25mV/RSENSE maximum 150mV/RSENSE. current comparator threshold sets peak inductor ripple current, yielding maximum output current IMAX equal peak value less half peak-to-peak ripple current. proper Burst Mode operation, IRIPPLE(P-P) must less than equal minimum current comparator threshold. Since efficiency generally increases with ripple current, maximum allowable ripple current assumed, i.e., IRIPPLE(P-P) 25mV/RSENSE. (See Selection Operating Frequency). Solving RSENSE allowing margin variations LTC1143 external component values yields:
MAXIMUM OUTPUT CURRENT
1143
RSENSE
RSENSE 100mV IMAX
Refer Functional Diagram Figure
threshold from increasing until output voltage dropped below minimum threshold. Using constant off-time architecture operating frequency function input voltage. minimize frequency variation dropout approached, off-time controller increases discharge current drops below VOUT 1.5V. dropout P-channel MOSFET turned continuously (100% duty cycle), providing extremely dropout operation.
graph selecting RSENSE versus maximum output current given Figure
0.20
0.15
0.10
0.05
Figure Selecting RSENSE
load current below which Burst Mode operation commences, IBURST, peak short circuit current, ISC(PK), both track IMAX. Once RSENSE been chosen, IBURST ISC(PK) predicted from following:
IBURST 15mV RSENSE
ISC(PK) 150mV RSENSE
LTC1143 automatically extends tOFF during short circuit allow sufficient time inductor current decay between switch cycles. resulting ripple current causes average short-circuit current ISC(AVG) reduced approximately IMAX.
LTC1143
APPLICATIONS INFORMATION
Selection Operating Frequency Each regulator section LTC1143 uses constant offtime architecture with tOFF determined external timing capacitor Each time P-channel MOSFET switch turns voltage reset approximately 3.3V. During off-time, discharged current which proportional VOUT. voltage analogous current inductor which likewise decays rate proportional VOUT. Thus inductor value must track timing capacitor value. value calculated from desired continuous mode operating frequency:
VOUT
Where drop across diode. graph selecting versus frequency including effects input voltage given Figure
1000 VSENSE VOUT
CAPACITANCE (pF)
FREQUENCY (kHz)
LTC1143
Figure Timing Capacitor Value
operating frequency increased gate charge losses will higher, reducing efficiency (see Efficiency Considerations). complete expression operating frequency circuit Figure given
tOFF
VOUT
Where:
tOFF
VREG VOUT
VREG desired output voltage (i.e., 3.3V). VOUT measured output voltage. Thus VREG/V regulation. Note that decreases, frequency decreases. When input output voltage differential drops below 1.5V particular section, LTC1143 reduces tOFF that section increasing discharge current This prevents audible operation prior dropout. Once frequency been inductor must chosen provide more than 25mV/RSENSE peakto-peak inductor ripple current. This results minimum required inductor value LMIN RSENSE VREG inductor value increased from minimum value, requirements output capacitor eased expense efficiency. small inductor used inductor current will become discontinuous before LTC1143 enters Burst Mode operation. consequence this that LTC1143 will delay entering Burst Mode operation efficiency will degraded currents. Inductor Core Selection Once minimum value known, type inductor must selected. highest efficiency will obtained using Ferrite, Kool Molypermalloy (MPP) cores. Lower cost powdered iron cores provide suitable performance, efficiency Actual core loss independent core size fixed inductor value, very dependent inductance selected. inductance increases, core losses down. Unfortunately, increased inductance requires more turns wire therefore copper losses will increase. Ferrite designs have very core loss, design goals concentrate copper loss preventing saturation.
Kool registered trademark Magnetics, Inc.
LTC1143
APPLICATIONS INFORMATION
Ferrite core material saturates "hard," which means that inductance collapses abruptly when peak design current exceeded. This results abrupt increase inductor ripple current consequent output voltage ripple which cause Burst Mode operation falsely triggered. allow core saturate! Kool (from Magnetics, Inc.) very good, loss core material toroids with "soft" saturation characteristic. Molypermalloy slightly more efficient high kHz) switching frequencies quite more expensive. Toroids very space efficient, especially when several layers wire. Because they generally lack bobbin, mounting more difficult. However, designs surface mount available from Coiltronics Beckman Industrial Corporation which increase height significantly. Power MOSFET Selection external power MOSFET must selected with each section LTC1143. main selection criteria power MOSFETs threshold voltage VGS(TH) resistance RDS(ON). minimum input voltage determines whether standard threshold logic-level threshold MOSFET must used. standard threshold MOSFETs (VGS(TH) used. expected drop below logic-level threshold MOSFETs (VGS(TH) 2.5V) strongly recommended. When logic-level MOSFETs used, LTC1143 supply voltage must less than absolute maximum ratings MOSFET. maximum output current IMAX determines RDS(ON) requirement MOSFETs. When LTC1143 operating continuous mode, simplifying assumption made that either MOSFET Schottky diode always conducting average load current. duty cycles MOSFET diode given From duty cycles required RDS(ON) each MOSFET derived:
P-Ch Duty Cycle VOUT Schottky Diode Duty Cycle
P-Ch RDS(ON)
VOUT IMAX2
where allowable power dissipation temperature dependencies RDS(ON). will determined efficiency and/or thermal requirements (see Efficiency Considerations). generally given MOSFET form normalized RDS(ON) temperature curve, 0.007/°C used approximation voltage MOSFETs. Output Diode Selection (D1, Schottky diodes shown Figure conduct during off-time. important adequately specify diode peak current average power dissipation exceed diode ratings. most stressful condition output diode under short circuit (VOUT=0). Under this condition diode must safely handle ISC(PK) close 100% duty cycle. Under normal load conditions average current conducted diode
VOUT IDIODE (ILOAD)
Remember keep lead lengths short observe proper grounding (see Board Layout Checklist) avoid ringing increased dissipation. forward voltage drop allowable diode calculated from maximum short circuit current
ISC(PK)
where allowable power dissipation will determined efficiency and/or thermal requirements (see Efficiency Considerations).
LTC1143
APPLICATIONS INFORMATION
COUT Selection continuous mode, source current P-channel MOSFET square wave duty cycle VOUT/VIN. prevent large voltage transients, input capacitor sized maximum current must used. maximum capacitor current given
Required IRMS IMAX [VOUT(VIN VOUT)]1/2
COUT (µF)
This formula maximum 2VOUT, where IRMS IOUT/2. This simple worst case condition commonly used design because even significant deviations offer much relief. Note that capacitor manufacturer's ripple current ratings often based only 2000 hours life. This makes advisable further derate capacitor, choose capacitor rated higher temperature than required. Several capacitors also paralleled meet size height requirements design. Always consult manufacturer there question. additional 0.1µF ceramic capacitor also required each line (pin high frequency decoupling. selection COUT driven required effective series resistance (ESR). COUT must less than twice value RSENSE proper operation LTC1143: COUT required 2RSENSE Optimum efficiency obtained making equal RSENSE. increased 2RSENSE efficiency degrades less than greater than 2RSENSE, voltage ripple output capacitor will prematurely trigger Burst Mode operation, resulting disruption continuous mode efficiency which several percent. Manufacturers such Nichicon United Chemicon, should considered high performance capacitors. OS-CON semiconductor dielectric capacitor available
from Sanyo lowest size/ratio aluminum electrolytic somewhat higher price. Once requirement COUT been current rating generally exceeds IRIPPLE(P-P) requirement. surface mount applications multiple capacitors have parallel meet capacitance, ESR, current handling requirements application. Aluminum electrolytic tantalum capacitors both available surface mount configurations. case tantalum critical that capacitors surge tested switching power supplies. excellent choice series surface mount tantalums, available case heights ranging from 4mm. example, 200µF/10V called application requiring height, 100µF/10V (P/N TPSD 107K010) could used. Consult manufacturer other specific recommendations.
1000 50µH RSENSE 0.02 25µH RSENSE 0.02
50µH RSENSE 0.05
VOUT VOLTAGE
1143
Figure Minimum Value COUT
supply voltages minimum capacitance COUT needed prevent abnormal frequency operating mode (see Figure When COUT made small output ripple frequencies will large enough trip voltage comparator. This causes Burst Mode operation activated when LTC1143 would normally continuous operation. output remains regulation times.
LTC1143
APPLICATIONS INFORMATION
Checking Transient Response regulator loop response checked looking load transient response. Switching regulators take several cycles respond step (resistive) load current. When load step occurs, VOUT shifts amount equal ILOAD ESR, where effective series resistance COUT. ILOAD also begins charge discharge COUT until regulator loop adapts current change returns VOUT steady-state value. During this recovery time VOUT monitored overshoot ringing which would indicate stability problem. 15(7) external components shown Figure circuit will prove adequate compensation most applications. second, more severe transient caused switching loads with large (>1µF) supply bypass capacitors. discharged bypass capacitors effectively parallel with COUT causing rapid drop VOUT. regulator deliver enough current prevent this problem load switch resistance driven quickly. only solution limit rise time switch drive that load rise time limited approximately CLOAD. Thus 10µF capacitor would require 250µs rise time, limiting charging current about 200mA. Efficiency Considerations percent efficiency switching regulator equal output power divided input power times 100%. often useful analyze individual losses determine what limiting efficiency which change would produce most improvement. Percent efficiency expressed %Efficiency 100% where etc. individual losses percentage input power. (For high efficiency circuits only small errors incurred expressing losses percentage output power.) Although dissipative elements circuit produce losses, four main sources usually account most losses LTC1143 circuits: LTC1143 bias current MOSFET gate charge current losses Voltage drop Schottky diode. supply current current which flows into (pin 3.3V section, section) less gate charge current. LTC1143 supply current each section 160µA load, increases proportionally with load constant 1.6mA after LTC1143 entered continuous mode. Because bias current drawn from VIN, resulting loss increases with input voltage. VIN=10V bias losses generally less than load currents over 30mA. However very load currents bias current accounts nearly loss. MOSFET gate charge current results from switching gate capacitance power MOSFET. Each time MOSFET gate switched from high again, packet charge moves from ground. resulting dQ/dt current which typically much larger than supply current. continuous mode, IGATECHG (QP). typical gate charge 125m P-channel power MOSFET 40nC. This results IGATECHG 100kHz continuous operation, typical mid-current loss with 10V. Note that gate charge loss increases directly with both input voltage operating frequency. This principal reason highest efficiency circuits operate moderate frequencies. Furthermore, argues against using larger MOSFET than necessary control losses, since overkill cost efficiency well money! losses easily predicted from resistances MOSFET, inductor, current shunt. continu mode average output current flows through RSENSE, "chopped" between P-channel MOSFET Schottky diode. MOSFET RDS(ON) multiplied P-channel duty cycle summed with resistances RSENSE obtain losses. example, RDS(ON) 0.1, 0.15, RSENSE 0.05, then total resistance 0.3. This results losses ranging from output
LTC1143
APPLICATIONS INFORMATION
current increases from 0.5A losses cause efficiency roll high output currents. Schottky diode major source power loss high currents gets worse high input voltages. diode loss calculated multiplying forward voltage drop times Schottky diode duty cycle multiplied load current. example, assuming duty cycle with Schottky diode forward voltage drop 0.4V, loss increases from 0.5% load current increases from 0.5A Schotky diode losses routinely exceed consider using synchronously switched LTC1142. Figure shows efficiency losses section typical LTC1143 regulator being apportioned. gate charge loss responsible majority efficiency lost mid-current region. Burst Mode operation employed currents, gate charge loss alone would cause efficiency drop unacceptable levels. With Burst Mode operation, supply current represents lone (and unavoidable) loss component which continues become higher percentage output current reduced. expected, losses Schottky diode loss dominate high load currents.
GATE CHARGE
LTC1143
EFFICIENCY
SCHOTTKY DIODE
0.01
0.03
OUTPUT CURRENT
LTC1143
Figure Efficiency Loss
Other losses including COUT dissipative losses, MOSFET switching losses, inductor core losses, generally account less than total additional loss.
Design Example design example, assume 12V(nominal), section, IMAX 200kHz, RSENSE, immediately calculated: RSENSE5 100mV 0.05 tOFF (1/200kHz) (5/12)] 2.92µs 2.92µs/(1.3 104) 220pF L2MIN 0.05 220pF 28µH Assume that MOSFET dissipation limited 250mW. 50°C thermal resistance MOSFET 50°C/W, then junction temperatures will 63°C 0.007(63-25) 0.27. required RDS(ON) MOSFET calculated:
P-Ch RDS(ON) 12(0.25) 0.12 5(2)2 (1.27)
P-channel requirement Si9430DY. Note that most stringent requirement Schottky diode with VOUT (i.e. short circuit). During continuous short circuit, worst case Schottky diode dissipation rises
ISC(AVG)
VOUT
With 0.05 sense resistor ISC(AVG) will result, increasing 0.4V Schottky diode dissipation 0.8W. will require current rating least temperature, COUT will require 0.05 optimum efficiency. allow drop minimum value. lower input voltages operating frequency will decrease P-channel will conducting most time causing power dissipation increase. VIN(MIN) frequency shifts 49kHz P-channel power dissipation increases 435mW. Check assure maximum temperature P-channel exceeded.
LTC1143
APPLICATIONS INFORMATION
Troubleshooting Hints Since efficiency critical LTC1143 applications very important verify that circuit functioning correctly both continuous Burst Mode operation. waveform monitor voltage timing capacitor continuous mode (ILOAD IBURST) voltage should sawtooth with 0.9VP-P swing. This voltage should never below shown Figure When load currents (ILOAD IBURST) Burst Mode operation occurs. voltage falls ground periods time shown Figure observed falling ground high output currents, indicates poor decoupling improper grounding. Refer Board Layout Checklist.
3.3V
CONTINUOUS MODE OPERATION 3.3V
Burst Mode OPERATION
Figure Waveforms
Auxiliary Windings--Suppressing Burst Mode Operation LTC1143 being nonsynchronous switch normal limitation that power drawn from inductor primary winding must less than twice power drawn from auxiliary windings. (With synchronous switching, using LTC1142, auxiliary outputs loaded without regard primary output load, providing that loop remains continuous mode operation.) Burst Mode operation suppressed output currents with simple external network which cancels 25mV minimum current comparator threshold. This technique also useful eliminating audible noise from
certain types inductors high current (IOUT >5A) applications when they lightly loaded. external offset series with Sense- subtract from built-in 25mV offset. example this technique shown Figure resistors inserted series with sense leads from sense resistor.
SENSE [PIN (8)] 1000pF SENSE [PIN 1(19)] RSENSE VOUT
COUT
1143
Figure Suppression Burst Mode Operation
With addition current generated though causing offset VOFFSET VOUT
LTC1143
VOFFSET 25mV, built-in offset will cancelled Burst Mode operation prevented from occurring. Since VOFFSET constant, maximum load current also decreased same offset. Thus, back same IMAX, value sense resistor must lower:
RSENSE 75mV IMAX
prevent noise spikes from erroneously tripping current comparator, 1000pF capacitor needed across pins (16) (8). Board Layout Checklist When laying printed circuit board, following checklist should used ensure proper operation LTC1143. These items also illustrated graphically layout diagram Figure general each block
LTC1143
APPLICATIONS INFORMATION
should self-contained with little cross coupling best performance. Check following your layout: signal power grounds segregated? LTC1143 ground (11) must return separately power, signal grounds. power ground returns anode Schottky diode plate CIN, which should have short lead lengths possible.The signal ground connects plate COUT. Does LTC1143 Sense- connect point close RSENSE plate COUT? Sense- Sense+ leads routed together with minimum trace spacing? 1000pF capacitor
P-CH
VIN5
CIN5
BOLD LINES INDICATE HIGH CURRENT PATHS SHUTDOWN OUTPUT)
GND5 SHUTDOWN P-DRIVES5 SENSE
0.0033µF
SENSE
ITH3
VIN3
1000pF*
SHUTDOWN SENSE
LTC1143
SENSE
0.22µF*
P-DRIVES3 VIN5
GND3
SHUTDOWN (3.3V OUTPUT)
VIN5 0.0033µF
RSENSE3
P-CH
VOUT3 COUT3
ITH5
Figure LTC1143 Layout Diagram (see Board Layout Checklist)
between pins should close possible LTC1143. Does plate connect source P-channel MOSFET closely possible? This capacitor provides current P-Channel MOSFET. decoupling capacitor (1µF, 0.1µF) connected closely between ground (11)? This capacitor carries MOSFET driver peak currents. Shutdown pins actively pulled ground during normal operation? Both shutdown pins high impedance must allowed float. Both pins driven same external signal needed.
RSENSE5
COUT5 VOUT5
VIN3
1000pF* 0.22µF*
CIN3 VIN3
*MUST LOCATED CLOSE LTC1143
1143
LTC1143
TYPICAL APPLICATIONS
5.2V CIN3 22µF 50µH
P-CH Si9430DY 0.01µF VIN3
VOUT3 3.3V/1A
RSENSE3 0.10
COUT3 220µF
MBRD330
RSENSE3: LR2512-01-OR100G RSENSE5: LR2512-01-ORO5OG
Figure Surface Mount Dual 5V/2A, 3.3V/1A Converter
CIN3 22µF
P-CH Si9430DY 0.01µF VIN3
VOUT3 3.3V/2A
RSENSE3 0.05
25µH
OUT3
220µF
MBRD330
RSENSE3: SL-1/2-C1-0R050J RSENSE5: SL-1/2-C1-0R050J
Figure Surface Mount Dual 5V/2A, 3.3V/2A Converter
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.
0.22µF NORMAL >1.5V SHUTDOWN SHUTDOWN SHUTDOWN 0.22µF
VIN5 P-DRIVE SENSE SENSE 0.01µF P-CH Si9430DY
CIN5 22µF 25µH
P-DRIVE SENSE SENSE
RSENSE5 0.05
VOUT5 5V/2A
LTC1143
GND3
ITH3 270pF
ITH5
GND5
MBRD330
COUT5 220µF
3300pF
3300pF
220pF
LTC1143.F10
CIN3, CIN5: (TA) TPSD226K025R0200 COUT3, COUT5: (TA) TPSE227K010R0080
COILTRONICS CTX50-4 COILTRONICS CTX25-4
5.2V
0.22µF SHUTDOWN NORMAL >1.5V SHUTDOWN 0.22µF SHUTDOWN
VIN5 P-DRIVE SENSE LTC1143 SENSE 0.01µF P-CH Si9430DY
CIN5 22µF 25µH RSENSE5 0.05
P-DRIVE SENSE SENSE
VOUT5 5V/2A
GND3
ITH3 330pF 3300pF
ITH5
GND5
MBRD330
COUT5 220µF
3300pF
220pF
LTC1143.F11
CIN3, CIN5: (TA) TPSD226K025R0200 COUT3, COUT5: (TA) TPSE227K010R0080
COILTRONICS CTX25-4 COILTRONICS CTX25-4
LTC1143
PACKAGE
0.010 0.020 (0.254 0.508) 0.008 0.010 (0.203 0.254)
0.016 0.050 0.406 1.270
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7487
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
Dimensions inches (millimeters) unless otherwise noted.
Package 16-Lead Plastic SOIC
0.386 0.394* (9.804 10.008)
0.228 0.244 (5.791 6.197)
0.150 0.157* (3.810 3.988)
0.053 0.069 (1.346 1.752)
0.004 0.010 (0.101 0.254)
0.014 0.019 (0.355 0.483)
0.050 (1.270)
SO16 0392
*THESE DIMENSIONS INCLUDE MOLD FLASH PROTRUSIONS. MOLD FLASH PROTRUSIONS SHALL EXCEED 0.006 INCH (0.15mm).
LT/GP 0394 PRINTED
LINEAR TECHNOLOGY CORPORATION 1994

LTC1143 dual step-down switching regulator controller featuring automa

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