1.5A, 1.5 MHZ ADJUSTABLE,
STEP-DOWN SWITCHING REGULATOR IN DFN6
I
II
I
II
III
STEP-DOWN CURRENT MODE PWM (1.5MHz) DC-DC CONVERTER
2% DC OUTPUT VOLTAGE TOLERANCEINTERNAL SOFT START FOR START-UP CURRENT LIMITIATION AND POWER ON DELAY OF 50-100µs
TYPICAL EFFICIENCY: > 70% OVER ALL OPERATING CONDITIONS
1.5A OUTPUT CURRENT CAPABILITY
NOT SWITCHING QUIESCENT CURRENT: MAX 2.5mA OVER TEMPERATURE RANGE SWITCH VDS: MAX 350mV @ISW=750mAUSES TINY CAPACITORS AND INDUCTORS AVAILABLE IN DFN 3x3 EXPOSED PAD
DFN6 (3x3)DESCRIPTION
The ST1S03 is a step down DC-DC converteroptimized for powering low-voltage digital core inHDD applications and, generally, to replace thehigh current linear solution when the powerdissipation may cause an high heating of theapplication environment. It provides up to 1.5Aover an input voltage range of 3V to 16V. An highFigure 1: Schematic Diagramswitching frequency (1.5MHz) allows the use oftiny surface-mount components: as well as theresistor divider to set the output voltage value,only an inductor, a schottky diode and twocapacitors are required. Besides, a low outputripple is guaranteed by the current mode PWMtopology and by the use of low E.S.R. SMDceramic capacitors. The device is thermalprotected and current limited to prevent damagesdue to accidental short circuit. The ST1S03 isavailable in DFN6 package.
March 2005
Rev. 31/11
ST1S03
Table 1: Order Codes
SYMBOLST1S03
DFN6ST1S03PM
(Tape & Reel)ST1S03RPM
Figure 2: Pin Connection (top through view)
Table 2: Pin Description
PIN N°123456
SymbolVFBGNDSWVIN_SWVIN_AN.C.
Voltage of Feedback
Sistem Ground
Output of the internal Power SwithchPower Supply for the MOSFET SwitchPower Supply for the Analog CircuitNot Connected
Name and Function
Table 3: Absolute Maximum Ratings
SymbolVI_SWVI_SW
Parameter
Positive Power Supply VoltagePositive Power Supply Voltage
Value-0.3 to 16-0.3 to 16-0.3 to 162.5±1150-25 to 150300
UnitVVVVmA°C°C°C
SWITCH Max Voltage of output pinVoltageVFBIVFBTJTSTGTLEAD
Feedback Voltage
Common mode input voltageMax Junction TemperatureStorage Temperature Range
Lead Temperature (Soldering) 10 Sec.
Absolute Maximum Ratings are those beyond which damage to the device may occur. Functional operation under these condition is not im-plied.
Table 4: Thermal Data
SymbolRTHJ-CRTHJ-A
Parameter
Thermal Resistance Junction-case Thermal Resistance Junction-ambient
DFN61055
Unit°C/W°C/W
2/11
ST1S03
Table 5: Electrical Characteristics (VIN_SW = VIN_A = 5V, CI = 4.7µF, CO = 22µF, L1 = 3.3µH, TJ = 0 to 125°C, unless otherwise specified. Typical values are referred to 25°C)
SymbolFBPSRRIFBBWIQIOUTIMIN%VOUT/∆VIN%VOUT/∆IOUTPWM fSDMAXISWLVDSETSHDNTHYS∆VOUT/∆IOUT
Parameter
Feedback VoltageFeedback PSRRVFB Pin Bias Current
Bandwidth of Error AmplifierClosed LoopQuiescent CurrentNo SwitchingOutput Current
Minimum Output CurrentReference Line RegulationReference Load RegulationPWM Switching Frequency (1)
Maximum Duty CycleSwitching Current LimitationSwitch VDSEfficiency
Thermal Shut Down (1)Thermal Shut Down Hysteresis (1)
Load Transient Response (1)
ISW = 750 mAIOUT =10mA to 1.2A
70130
15015
IOUT = 100mA to 700mAtR = tF ≥ 100ns, TA = 25°CIOUT = 10mA to short, TA = 25°C
-5
+5+5
VIN = 3V to 16VIOUT = 10mA to 1.2AVFB = 0.8V, TA =25°C
1.2
VIN =3V to 16V
1.51
0.0320.00141.587
1.65
200
3500.060.0031.8
300
2.5
Test Conditions
1Hz < Frequency VIN
Min.784
Typ.800-60
Max.816600
UnitmVdBnAKHzmAAmA%VOUT/∆VIN%VOUT/mAMHz%AmV%°C°C%VO%VO
Short Circuit Removal ∆VOUT/
Response (1)∆IOUT
@IO = short
NOTE 1: Guaranteed by design, not tested in production.
3/11
ST1S03
APPLICATION NOTES
The ST1S03 is an adjustable current mode PWMstep-down DC/DC converter with internal 1.5Apower switch, packaged in a 6-lead DFN 3x3.It’s a complete 1.5A switching regulator with itsinternal compensation eliminating additionalcomponent.
The constant frequency, current mode, PWMarchitecture and stable operation with ceramiccapacitors results in low, predictable output ripple.However, in order to keep the output regulated,the devices goes in pulse skipping mode when avery light load is required.
To clamp the error amplifier reference voltage aSoft Start control block generating a voltage ramp,has been implemented. Besides an On-ChipPower on Reset of 50 = 100µs ensure the properoperation when switching on the power supply.Other circuits fitted to the device protection are theThermal Shut down block which turn off theregulator when the junction temperature exceeds150°C typically and the Cycle-by-cycle CurrentLimiting that provides protection against shortedoutputs.
Being the ST1S03 an adjustable regulator, theoutput voltage is determined by an externalFigure 3: Application Circuit
resistor divider. The desired value is given by thefollowing equation:VOUT = VFB [1+R1/R2]
To make the device working, only other fourexternal components are required: a Schottkydiode, an inductor and two capacitors. The choseninductor must be able to not saturate at the peakcurrent level. Besides, its value can be selectedkeeping in account that a large inductor valueincreases the efficiency at low output current andreduces output voltage ripple, while a smallerinductor can be chosen when it is important toreduce the package size and the total cost of theapplication. Finally, the ST1S03 has beendesigned to work properly with X5R or X7R SMDceramic capacitors both at the input and at theoutput. this kind of capacitors, thanks to their verylow series resistance (ESR), minimize the outputvoltage ripple. Other low ESR capacitors can beused according to the need of the applicationwithout invalidating the right functioning of thedevice. Due to the high switching frequency andpeak current, it is important to optimize theapplication environment reducing the length of thePCB traces and placing all the externalcomponent near the device.
4/11
ST1S03
TYPICAL CHARACTERISTICS (CIN = 4.7µF, CO = 22µF, L1 = 3.3µH, unless otherwise specified)Figure 4: Load Voltage Feedback vs Temperature
Figure 7: Line Voltage Feedback vs Temperature
Figure 5: Voltage Feedback vs Temperature Figure 8: Voltage Feedback vs Output Current
Figure 6: Line Output Voltage Regulation vs Temperature Figure 9: PWM Switching Frequency vs Temperature
5/11
ST1S03
Figure 10: Quiescent Current vs Temperature
Figure 13: Efficiency vs Temperature
Figure 11: Quiescent Current vs Input Voltage Figure 14: Efficiency vs Output Current
Figure 12: Minimum Operating Voltage vs Output Voltage Figure 15: Switch VDS vs Temperature
6/11
ST1S03
Figure 16: Switch RDS-ON vs Temperature
Figure 19: Load Transient Response
VCC=5V, IO=200mA to 1.2A, CI=4.7µF, CO=22µF, L=3.3µH, TON=38µs, TJ=25°C
Figure 17: Switch Current Limitation vs Temperature Figure 20: Start-Up Transient
VCC = 5V, TJ = 25°C
Figure 18: Load Transient Response Figure 21: Start-Up Transient
VCC=5V, IO=100mA to 780mA, CI=4.7µF, CO=22µF, L=3.3µH, TON=38µs, TJ=25°C
VCC = 5V, TJ = 25°C
7/11
ST1S03
DFN6 (3x3) MECHANICAL DATA
mm.
DIM.
MIN.
AA1A2A3bDD2EE2eLL1L2K
0.200.20
0.24
0.13
7.9
0.332.901.922.901.11
0.95
0.45
7.9
9.4
5.1
3.003.00
0.8000.65
0.20
0.433.102.123.101.31
13.0114.275.6114.243.7
37.4
17.7
118.1118.1
TYP
MAX.1.000.050.75
MIN.31.50.025.6
7.9
16.9122.083.5122.051.6
TYP.
MAX.39.42.029.5
inch
7387339A8/11
ST1S03
Tape & Reel QFNxx/DFNxx (3x3) MECHANICAL DATA
mm.
DIM.
MIN.
ACDNTAoBoKoPoP
3.33.31.148
12.820.299
10114.4
0.1300.1300.0430.1570.315
TYP
MAX.33013.2
0.5040.7953.898
3.9760.567
MIN.
TYP.
MAX.12.9920.519
inch
9/11
ST1S03
Table 6: Revision History
Date11-Nov-200408-Feb-200503-Mar-2005
Revision
123
Description of Changes
First Release.Maturity Change.
Mistake on Figure 1, TJ is changed 125 ==> 150°C on Table 3.
10/11
ST1S03
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequencesof use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is grantedby implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subjectto change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are notauthorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.The ST logo is a registered trademark of STMicroelectronicsAll other names are the property of their respective owners
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11/11
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