ST755 Fast Delivery |IC PHOENIX CO.,LIMITED

ST755 ,ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORSELECTRICAL CHARACTERISTICS (Refer to the test circuits, V = 5V, V = -5.25 to -4.75V,CC outoI = 0mA, ..
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ST755
ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS
ST755
ADJUSTABLE INVERTING NEGATIVE OUTPUT
CURRENT MODE PWM REGULATORS
September 1998 2.7VTO 11VINPUTTO ADJUSTABLE
NEGATIVEOUTPUT CONVERSION 1W GUARANTEED OUTPUT POWER
(Vin>4.5V, T≤70oC) 68% TYP. EFFICENCYAT6V VERYLOW QUIESCENT CURRENT: 1.2mAON MODE 10μAIN SHUT DOWN MODE SOFT START VERYLOW NOISE OUTPUT 160KHz FIXED FREQUENCY OSCILLATOR MIXED BIPOLAR-CMOS TECHNOLOGY
DESCRIPTION
The ST755 is an adjustable inverting
switch-mode DC-DC rergulator with internal
Power MOSFET that generatersan adjustable
negative output froma voltage inputof 2.7Vto
11V, output current guaranteedat 200mA (for
BLOCK DIAGRAM
DIP-8 SO-8
Vin>4.5V, Vout= -5V and0oC≤Ta≤70oC) and
275mA (typical valueatTa =25oC, Vout= -5V). logic controlled shut downpin that interfaces
directly with microprocessor reduces supply
currentto only 10μA. Inputto Output differential
voltageis limitedto Vin+|Vout|<12.7V. No load
supply currentis 1.2mA.
1/9
Absolute Maximum Ratingare those values beyond which damageto thedevicemay occur.
Functional operation under these conditionisnot implied.
CONNECTION DIAGRAM AND (top view)
PIN CONNECTIONS
PinNo Symbol Nameand Function SHDN SHUT-DOWN Control (VCC=On, GND=Shutdown)
2Vref Reference Output Voltage (1.25V) SS Soft Start CC Compensation Input
5Vout Negative OutputVoltage GND Ground LX Switch Output
8VCC Positive Supply-Voltage Input
ORDERING NUMBERS
Type DIP-8 SO-8 (Tube) SO-8 (T&R)
ST755 ST755CN ST755CD ST755CD-TR
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
Vcc DC Input Voltageto GND -0.3to12 V
SHDN Shutdown Voltage -0.3to VCC+0.3 V
Other Input Voltage -0.3to VCC+0.3 V
ILX Peak Switch Current 2 A
Ptot Power Dissipation (at70oC)(for DIP-8)
(for SO-8)
Top Operating Ambient Temperature Range -40to85 oC
Tstg Storage Temperature Range -55to150 oC
ST755
2/9
ELECTRICAL CHARACTERISTICS (Refertothe test circuits, VCC=5V, Vout= -5.25to -4.75V,
Iload= 0mA,Ta =Tminto Tmax unless otherwise specified. Typical Valueare referredatTa =25oC)
Symbol Parameter Test Conditions Min. Typ. Max. Unit
VIN Input Voltage 2.7 11 V Output Voltage Io=0mAto200mA VCC=4.5to6.2V -5.25 -5 -4.75 V Output Current VCC=4.5to6.2VTa=0oCto70oC
VCC=4.5to6.2VTa=-40oCto85oC
VCC=4V Vout=-5V
VCC=2.7V Vout=-5V
ISUPPLY Supply Current (Including
Switching Current) Load, VSHDN=VCC 1.2 3.5 mA
IOFF StandbyCurrent No Load, VSHDN=0V 10 100 μA
ISC Short Circuit Current 1.2 A
ΔVo Line Regulation VCC=4to 6.2V 0.1 %/V
ΔVo LoadRegulation Io=0mAto200mA 0.003 %/mA
VREF Reference Voltage Ta =25oC 1.18 1.25 1.32 V
ΔVREF Reference Dritft Ta =Tmin toTmax 50 ppm/oC
RDSON LXOn Resistance 0.7 Ω
ILEAK LX Leakage Current VDS =10V 1 μA
ISH ShutdownPin Current 1 μA
Vil Shutdown InputLow Threshold 0.25 V
Vih Shutdown Input High
Threshold Oscillator Frequency 160 KHz Power Efficency Io= 100mA 68 % CompensationPin Impedance 7.5 KΩnot overloadorshortthe Outputto Ground.Ifthe above conditionsare observerd, thedevicemaybe damaged.
APPLICATION INFORMATION
The ST755is anIC developed for voltage
conversion froman input voltage ranging from
+2.4Vto 11Vtoa regulated adjustable negative
output limitedby |Vout|≤ 12.7V-VIN. The circuit
adoptsa current-mode PWM control schemeto
achieve good efficiency, high stability and low
noise performance. The figureinthe first page
shownthe detailed block diagramof the device.
ST755is realizedina BCD technologyin orderto
achieve high temperature stability, the best
REFERENCE precision,a very low quiescent
current and jitter free operations. The final stage built arounda 0.7Ω-2A P-Channel Power
MOS.A fractionof the output currentis splitted
outfor current detection.Internal clock frequency fixedto 160KHz. Error amplifier drives the
PWM comparatorin orderto keep0VontheCC
input.SoR3 andR4 resistorsare calculatedby
the following formulaeR4= (|Vout|/Vref)*R3 (seefig
1). ForR3 canbe choosen any value between
2KΩ and 20KΩ. Soft-Start (SS) inputisa voltage
dependent-output current limit (see figure9,
Switch Current Limitvs. SS Input Voltage).SS
pinis internally pulledto Vref througha 1.2 MΩ
resistor. Applyingan appropiate capacitoratSS
inputis possibleto obtaina soft-start current
limitation during powerup. Forcing Soft-Start (SS)
inputtoa lower voltage througha resistive
voltage driver (R1 and R2), the maximum LX
curent limit can be lowered according the
diagram showedin figure9. When SHDN inputis
low,the total current consumptionis reducedto
10μA.
ST755
3/9
APPLICATION CIRCUIT achievethe best performances from switching
power supply topology, particular careto layout
drawingis needed,in orderto minimize EMI and
obtainlow noise, jitter free operation moreover,it
ensures the full device functionality. Layout
design proposedon demoboard (see picture2)
helpsto lowerthe developingtime.
Wire lengths must be minimized, filter and
by-pass capacitors C1,C2 andC3 mustbe low
ESR type, placedas close possibleto the
integrated circuit. The 10μH inductor mustbe
chosen builtona core, taking care that saturation
current shouldbe higher thanthe peakLX switch
current. See the PEAK INDUCTOR CURRENT
vs. LOAD CURRENT graph( figure6)
Figure1: TYPICALAPPLICATION CIRCUIT
Figure2: Printed Demoboard
Symbol Pin
VCC 1
Vout 2
SHDN 3
GND 4
Component Values
Capacitor Value Unit Resistor Value Unit 47 μFR1 130 KΩ 100 μFR2 300 KΩ 82 pF R3 10 KΩ 1 μFR4 40.7 KΩ 10 μFR5 10 KΩ 47 pF
(*)R1and R2canbe omittedfor Iout<200mA.
(**)C6: Verylow noisebutpoor transient andload response speed.
(***)C3 (alternativetoC6): fastertransientandload response.
ST755
4/9
Figure5: Efficencyvs Load Current
Figure7: SwitchON Resistancevs Supply
Voltage
Figure6: Peak InductorCurrentvs Load Current
Figure8: Oscillator Frequencyvs Temperature Supply Voltage
Figure3: Load Currentvs Supply Voltage Figure4: Load Currentvs Supply Voltage
TYPICAL OPERATING CHARACTERISTICS
ST755
5/9
Figure11: Soft Start Delay Time
Figure9: Switch Current Limitvs Soft Start
Voltage
Figure10: Reference Voltagevs temperature
TYPICAL OPERATING CHARACTERISTICS (continued)
ST755
6/9

Partno	Mfg	Dc	Qty	Available	Descript
ST755		N/a	11	avai	ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS
ST755	ST	N/a	2510	avai	ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS