SC1531 PRELIMINARY April 1999 TEL:805-498-2111 FAX:805-498-3

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SC1531 PRELIMINARY April 1999 TEL:805-498-2111 FAX:805-498-3

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200mA SmartLDO
SC1531
PRELIMINARY April 1999
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
SC1531 designed maintain glitch-free 3.3V output when least inputs, (VIN) 3.3V (VAUX), present. Whenever exceeds predetermined threshold value, internal 3.3V linear regulator enabled, pulled high. When falls below lower threshold value, pulled internal linear regulator turned off. been designed drive gate external threshold P-channel MOSFET, which used connect 3.3V supply directly regulator output. This ensures uninterrupted 3.3V output even falls specification. typical RDS(ON) 400m recommended. When both supplies simultaneously available, drive (DR) will pulled High, turning external PMOS switch. internal detector upper threshold (for rising) 4.18V (typical) while lower threshold (for falling) 4.05V (typical) giving hysteresis approximately 130mV. SENSE pin, which connected load, connects internally inverting input error amplifier. enables tight regulation load voltage (while supply present) despite variations load current. SC1531 available popular SO-8 surface mount package.
FEATURES
Glitch-free transition between input sources Internal logic selects input source Gate drive external PMOS bypass switch detector with hysteresis regulated output voltage accuracy 200mA load current capability Remote sense
APPLICATIONS
Desktop Computers Network Interface Cards (NICs) PCMCIA/PCI Interface Cards Cardbus Technology Power supplies with multiple input sources
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Parameter Input Supply Voltage Auxiliary Supply Voltage Output Current Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) Thermal Impedance Junction Ambient Thermal Impedance Junction Case Symbol VAUX TSTG TLEAD Maximum -0.5 -0.5 +150 Units °C/W °C/W
ORDERING INFORMATION
Part Number SC1531CS
Package SO-8
Temp. Range (TJ) 125°C
Note: suffix `TR' tape reel packaging.
CONFIGURATION
View
(SOIC-8)
Rating
1999 SEMTECH CORP.
MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
DESCRIPTION
Name Function VAUX SENSE This main input supply nominally connection. This auxiliary input supply nominally 3.3V. Logic power ground. connection. Sense Connect load minimize voltage drop across traces. 3.3V output. Driver output external P-channel MOSFET pass element.
APPLICATION CIRCUIT
3.3V 0.1uF 4.7uF 0.1uF VAUX SENSE SC1531 4.7uF 0.1uF 3.3V
NOTE: External switch (Q1): Motorola MGSF1P02ELT1 equivalent (PMOS, typical Gate Threshold Voltage typical RDS(ON) 2.5V).
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
ELECTRICAL CHARACTERISTICS
Unless specified, 25°C, VAUX 3.3V, 200mA, 4.7µF. Values bold apply over full operating temperature range.
Parameter Supply Voltage Quiescent Current
Symbol
Test Conditions
Units
VAUX VAUX VAUX 3.3V,
10.0 11.0
10.0 12.0
Reverse Leakage From VAUX
IVIN
VAUX 3.6V,
-1.0
VAUX Supply Voltage Quiescent Current VAUX IQ(AUX) VAUX 3.3V, VAUX 3.3V, Reverse Leakage From
(1)(2)(3)
IVAUX
5.5V, VAUX
-7.0
-50.0 -100.0
Detect
Threshold Voltage Hysteresis
VTH(LO) VHYST VTH(HI)
Falling
3.90
4.05
4.20
High Threshold Voltage Output Voltage
Rising
4.30
20mA 4.3V 5.5V, 200mA 3.9V 4.3V, VAUX 3.3V, 200mA
3.267 3.300 3.333 3.234 3.000 0.12 0.40 0.60 3.366
Line Regulation
REG(LINE) REG(LOAD)
4.3V 5.5V
Load Regulation
20mA 200mA
0.12
0.40 0.60
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
ELECTRICAL CHARACTERISTICS
Unless specified, 25°C, VAUX 3.3V, 200mA, 4.7µF. Values bold apply over full operating temperature range.
Parameter SENSE SENSE Impedance
Symbol
Test Conditions
Units
RSENSE
Drive Voltage 4.3V 5.5V, 200µA VTH(LO), -200µA Peak Drive Current
(1)(5)
IDR(PK)
Sinking: 3.9V, Sourcing: 4.3V, 1.2nF, ramping measured from VTH(HI) 1.2nF, ramping down, measured from VTH(LO)
Drive High Delay
Drive Delay
(1)(5)
NOTES: Guaranteed design. Detect Thresholds page Recommended source impedance supply: 0.25. This will ensure that RSOURCE VHYST, thus avoiding toggling during detect threshold transitions. Application Circuit page Timing Diagram page
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
DETECT THRESHOLDS
NOTE: rise fall times (10% 90%) 100µs.
TIMING DIAGRAM
NOTE: rise fall times (10% 90%) 100ns.
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
TYPICAL CHARACTERISTICS
Junction Temperature
(mA) -5°C 25°C 125°C (mA) VAUX -5°C 25°C 125°C VAUX 3.3V
Junction Temperature
IQ(AUX) VAUX Junction Temperature
IQ(AUX) (mA) IQ(AUX) VAUX -5°C 25°C 125°C
IQ(AUX) VAUX Junction Temperature
-5°C 25°C 125°C VAUX
Output Voltage Junction Temperature
3.34 3.33 3.32 3.31 3.30 3.29 3.28 3.27 3.26 (°C) 200mA
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
TYPICAL CHARACTERISTICS
Drive High Delay
Drive Delay
Trace stepping from 5.5V Trace going high VTH(HI) 225ns
Trace stepping from 5.5V Trace going VTH(LO) 125ns
VO(min) With Rising
VO(min) With Falling
Trace charging 1500uF capacitor Trace going high VTH(HI) Trace offset 3.3V. VO(min) 3.19V
Trace discharging 1500uF capacitor Trace going VTH(LO) Trace offset 3.3V. VO(min) 3.14V
NOTES: Application Circuit page 200mA. 1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
TYPICAL CHARACTERISTICS
Load Transient Response
Load Transient Response
Trace Trace stepping from 200mA NOTE: Application Circuit page
Trace Trace stepping from 200mA
APPLICATIONS INFORMATION
Introduction SC1531 intended applications such power managed network interface cards (NICs), where operation from 3.3V VAUX supply required when supply been shut down. provides very simple, cost solution that uses very little real estate. During regular operation, 3.3V power card provided SC1531's onboard dropout regulator, generated from supply. When supply removed 3.3V VAUX available, SC1531 connects this supply directly output using tiny SOT-23 external pchannel FET. Component Selection Output capacitors Semtech recommends minimum bulk capacitance 4.7µF output, along with 0.1µF ceramic decoupling capacitor. Increasing bulk capacitance will improve overall transient response. device very tolerant capacitor value variations, fact, combination capacitors with 4.7µF sufficient stability. This target easily using surface mount ceramic tantalum capacitors.
Input capacitors (5V) Semtech recommends 4.7µF ceramic tantalum capacitor plus 0.1µF ceramic capacitor input. This allows device being some distance from bulk capacitance rail. Additionally, input droop load transients reduced, improving load transient response. Input capacitors (3.3V) Semtech recommends decoupling this with 0.1µF ceramic capacitor. P-channel bypass selection external determined main requirements: have very gate threshold (typically ~1V) order sufficiently turned with 3.3V. RDS(ON) must enough such that:
VAUX
Remember that 125°C, RDS(ON) generally 1.5x value 25°C. Thermal Considerations When operating from supply, power dissipation SC1531 approximately equal product output current input output voltage differential:
(VIN
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
APPLICATIONS INFORMATION (Cont.)
absolute worst-case dissipation given
(VIN VAUX
power dissipation given
200mA, RDS(ON) 0.6, 24mW. Layout Considerations While layout linear devices generally critical switching application, careful attention detail will ensure reliable operation. below sample layout. Attaching part larger copper footprint will enable better heat transfer from device, especially PCBs where there internal ground power planes. Place bulk decoupling capacitors close device optimal transient response. SENSE lead being used, route load using seperate trace from main path. being used, connect shown. external bypass shown close device convenience only. Since being switched, longer gate drive traces used without problem.
Note that VAUX(MAX) IQ(AUX) term does apply VAUX available. Inserting 5.5V, 3.234V, 200mA, VAUX 3.6V IQ(AUX) yields:
Using this figure, calculate maximum thermal impedance allowable maintain 125°C:
)(MAX
(MAX
PD(MAX
(125
0.46
)(MAX therefore )(MAX
This readily achievable using copper area conducting heat away from device (see below). Heatsinking bypass necessary
Copper Fig. Suggested layout based upon Application Circuit Page
Silk Screen
BILL MATERIALS
Qty. Reference Part/Description 0.1µF ceramic Vendor Various P-channel, gate threshold, 400m Notes
4.7µF ceramic tantalum Various MGSF1P02ELT1 SC1531CS Motorola Semtech
1999 SEMTECH CORP.
MITCHELL ROAD NEWBURY PARK 91320
200mA SmartLDO
SC1531
PRELIMINARY April 1999
OUTLINE DRAWING
JEDEC REF: MS-012AA
LAND PATTERN SO-8
1999 SEMTECH CORP. MITCHELL ROAD NEWBURY PARK 91320

SC1531 PRELIMINARY April 1999 TEL:805-498-2111 FAX:805-498-3

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