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ST735S
300kHz, -5V/ADJ INVERTING, NEGATIVE OUTPUT CURRENT-MODE PWM REGULATOR
1/11October 2002 CONVERTS +4.0VTO+ 6.2V INPUTTO-5V
OUTPUT (735S)OR +3.5VTO+ 9.0VTOA
NEGATIVE ADJUSTABLE OUTPUT (735T) 1W GUARANTEED OUTPUT POWER 72% TYPICAL EFFICIENCY 0.8mA QUIESCENT CURRENT 1μA SHUTDOWN MODE 300KHZ FIXED FREQUENCY OSCILLATOR CURRENT MODE PWM CONVERTER LOW NOISE AND JITTER SOFT START SIMPLE APPLICATION CIRCUIT UNDERVOLTAGE LOCKOUT (735S)
DESCRIPTIONThe ST735S/ST735Tisa Bi-CMOS, inverting
switch mode DC-DC regulator with internal Power
MOSFET that generatesa fixed-5V(S version)or negative adjustable(T version) output voltage
froma4V (3.5Vforthe 735T)to 6.2V input voltage
(9Vforthe 735T);is guaranteedan output current 200mA for inputs greater than 4.5V. The
quiescent currentfor this deviceis typicallyof
0.8mA and,in shutdown modeitis reducedto
1μA.
These power-conserving features, along with high
efficiency and applications circuits, thaT lend itself minaturization, make the ST735S/ST735T
excellentina broad rangeof on-card, HDD and
portable equipment applications. These device
employa high performance current mode pulse
with modulation (PWM) control schemeto provide
tight output voltage regulation andlow noise. The
fixed frequency oscillatoris factory trimmedto
300KHz, allowingfor easy noise filtering. The
regulatorin productionis testedto guaranteean
output accuracy within ±5% overall specified
conditions.
ST735S
ST735T300kHz, -5V/ADJ INVERTING, NEGATIVE OUTPUT
CURRENT-MODE PWM REGULATOR
SCHEMATIC DIAGRAM
ST735S/ST735T2/11
ABSOLUTE MAXIMUM RATINGSAbsoluteMaximum Ratingsare those values beyond which damagetothe devicemay occur. Functional operation under these conditionis
not implied.
Note1:The inputto output differential voltageis limitedto VIN+|VOUT|<12.7V
THERMAL DATA
CONNECTION DIAGRAM (top view)
PIN DESCRIPTION
ST735S/ST735T3/11
ORDERING CODES
TYPICAL APPLICATION CIRCUITNOTE:All capacitorsareX7R ceramicC5canbe omittedifareused higher valuesfortheinputand output capacitors (suggested C2=47μF, C1=100μF). R1and R2mustbe placedis ST735T applications only.Their valuesare calculatedbythe following formula R2=(|VOUT|/VREF)xR1.ForR1
canbe chosenany value between2kΩand 20kΩ
APPLICATION CIRCUIT achievethe best performances from switching
power supply topology, particular careto layout
drawingis needed,in orderto minimize EMI and
obtain low noise. Moreover, jitter free operation
ensuresthefull device functionality. Layout design
proposed on demoboard helpsto lower the
developing time. Wire lengths mustbe minimized,
filter and bypass capacitors mustbe low ESR
type, placedas closeas possibletothe integrated
circuit. The 4.7μF(or 6.8μF) inductor mustbe
chosen builtona core, taking care that saturation
current shouldbe higher thanthe peakLX switch
current. Seethe Peak Inductor Currentvs Output
Current graph.
PRINTED DEMOBOARD (notin scale)
ST735S/ST735T4/11
ELECTRICAL CHARACTERISTICSOF ST735S (Refertotest circuit,VIN =5V,CIN =4.7μF,COUT =10μF
all X7R ceramic,L= 4.7μH(Note1), IOUT=0mA, Tamb=-40to 125°C, unless otherwise specified. Typical
valueare referredatTamb= 25°C)
Note1: Utilizeof 6.8μH permitsto reach higher current capabilityatthe same operating conditions
Note2: Guaranteedby design,butnot testedin production
Note3: Testedat IVREF= 125μA
ST735S/ST735T5/11
ELECTRICAL CHARACTERISTICSOF ST735T (Refertotest circuit,VIN =5V,CIN =4.7μF,COUT =10μF
all X7R ceramic,L= 4.7μH (Note1), IOUT=0mA,VO adjustedto -5V, Tamb=-40to 125°C, unless otherwise
specified. Typical valueare referredat Tamb= 25°C)
Note1: Utilizeof 6.8μH permitsto reach higher current capabilityatthe same operating conditions
Note2: Guaranteedby design,butnot testedin production
Note3: Testedat IVREF= 125μA
ST735S/ST735T6/11
TYPICALCHARACTERISTICS (Referredto typical application circuit,Tamb =25°C unless otherwise specified)
Figure1: Output Voltagevs Temperature
Figure2: Reference Voltagevs Temperature
Figure3: EfficencyvsTemperature
Figure4: Efficencyvs Ouput Current
Figure5: Efficencyvs Low Ouput Current
Figure6: Supply Currentvs Temperature
