400mA SmartLDOwith Internal Pass MOSFET Glitch-free transition be

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400mA SmartLDOwith Internal Pass MOSFET Glitch-free transition be

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Intended applications such Power Managed PCI, SC1532 designed maintain glitch-free 3.3V output when least inputs, (VIN1) 3.3V (VIN2), present. SC1532 combines 3.3V linear regulator with integral 3.3V bypass switch, along with logic detection circuitry control which supply provides power output. Whenever VIN1 exceeds predetermined threshold value, internal 3.3V PMOS linear regulator enabled, internal pass NMOS turned off. When VIN1 falls below lower threshold value, NMOS pass device turned PMOS linear regulator turned off. This ensures uninterrupted 3.3V output even VIN1 falls specification. When both supplies simultaneously available, PMOS linear regulator will turned NMOS pass device will turned off, thus preferentially supplying output from supply. internal detector upper threshold (for VIN1 rising) 4.18V (typical) while lower threshold (for falling) 4.1V (typical) giving hysteresis approximately 80mV. SC1532 available popular SO-8 surface mount package.
400mA SmartLDOwith Internal Pass MOSFET
Glitch-free transition between input sources Internal logic selects input source detector with hysteresis regulated output voltage accuracy 400mA load current capability SO-8 package
SC1532
Applications
Desktop Computers Network Interface Cards (NICs) PCMCIA/PCI Interface Cards Peripheral Cards
Typical Application Circuit
3.3VAUX 3.3V VIN2 VIN1
SC1532 4.7uF 4.7uF 4.7uF
Notes: Ceramic capacitors recommended Applications Information further details. Output capacitor needs 1.0µF greater stability. Additional capacitance (tantalum ceramic) will improve overall performance.
Revision December 2000
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SC1532
POWER MANAGEMENT Absolute Maximum Ratings
Parameter Input Supply Voltages harge Pump apaci Voltage Output urrent Thermal Impedance Juncti Ambi ent(1) Operati Ambi Temperature Range Operati Juncti Temperature Range Storage Temperature Range Lead Temperature (Solderi Rati (Human Body Model) mbol VIN1, VIN2 TSTG TLEAD Maximum -0.5 -0.5 +125 +150 nits
Note: inch square 1/16 FR-4, double sided, minimum copper weight.
Electrical Characteristics
Unless specified: 25°C, VIN1 VIN2 3.3V, 400mA, CIN1 CIN2 4.7µF, 1nF. Values bold apply over full operating temperature range.
Parameter Supply Voltage escent urrent
mbol
Test onditions
nits
VIN1
VIN2 VIN1 VIN2 3.6V,
Reverse Leakage From VIN2(1) Supply Voltage escent urrent
IVIN1
VIN1 VIN2 3.6V,
VIN2 VIN2 3.3V, VIN1 5.5V,
1300 2000
Reverse Leakage From VIN1(1) etect(1)(2) Threshold Voltage Hysteresi Threshold Voltage
IVIN2
VIN1 5.5V, VIN2
VTH(LO) VHYST VTH(HI)
VIN1 Falli 20mA 20mA VIN1 20mA
3.90
4.10 4.18 4.30
2000 Semtech Corp.
www.semtech.com
SC1532
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: 25°C, VIN1 VIN2 3.3V, 400mA, CIN1 CIN2 4.7µF, 1nF. Values bold apply over full operating temperature range.
Parameter Output Voltage Accuracy
mbol
Test onditions
nits
20mA 4.3V VIN1 5.5V, 400mA(1) 3.9V VIN1 4.3V, VIN2 3.3V, 400mA(1)
3.000
VIN2 Pass Resi stance (Aux. NMOS)(1)(3) Regulati
RDS(ON) REG(LINE)
VIN1 3.9V, 400mA VIN1 4.3V 5.5V
Load Regulati
REG(LOAD)
20mA 400mA
urrent Limit Output urrent ILIM VIN1 VIN2 1200 1400 Temperature Protection Level Hysteresi THYS VIN1 VIN1=
Notes: Guaranteed design. Recommended source impedance supply: 0.125W. This will ensure clean transitions between supplies with chattering (see Applications Information). Refer block diagram.
2000 Semtech Corp.
www.semtech.com
SC1532
POWER MANAGEMENT Configuration
VIEW
Ordering Information
Part umber(1) 1532C S.TR ackag SO-8
Note: Only available tape reel packaging. reel contains 2500 devices. SO-8
Block Diagram
Descriptions
VIN2 VIN1 Function Secondary nput supply, nomi nally 3.3V. nput supply nomi nally 3.3V output. harge pump capaci connecti Ground
2000 Semtech Corp.
www.semtech.com
SC1532
POWER MANAGEMENT Typical Characteristics
Quiescent Current (IQ1) Junction Temperature VIN2
VIN2 3.6V (mA) VIN2 (°C) VIN1 (°C) VIN2 3.3V (µA) VIN1 5.5V VIN1
Quiescent Current (IQ2) Junction Temperature VIN1
Output Voltage Junction Temperature Output Current
3.310 3.305 3.300 3.295 3.290 3.285 3.280 3.275 3.270 (°C) 400mA REG(LINE) 200mA VIN1 VIN2 3.3V 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.40 0.35
Line Regulation Junction Temperature
VIN1 4.3V 5.5V 400mA
(°C)
Load Regulation Junction Temperature
0.40 0.35 0.30 REG(LOAD) ILIM (mA) 0.25 0.20 0.15 0.10 0.05 0.00 (°C) VIN1 VIN2 3.3V 20mA 400mA 1200 1000
Current Limit Junction Temperature
VIN1 VIN2
(°C)
2000 Semtech Corp.
www.semtech.com
SC1532
POWER MANAGEMENT Typical Characteristics (Cont.)
VIN2 Pass Device Resistance Junction Temperature
RDS(ON) 4.00 (°C) 3.95 3.90 (°C) 4.15 4.10 VTH(LO) 4.05 VIN1 VIN2 3.3V 400mA 4.30 4.25 4.20 VIN2 3.3V 20mA VTH(HI)
Detect Threshold Voltage Junction Temperature
VO(MIN) With VIN1 Rising(1)(2)
VO(MIN) With VIN1 Falling(1)(2)
Trace offset 3.3V, 100mV/div Trace VIN1 rising through VTH(HI), 2V/div VO(MIN) 3.11V Notes: Application Circuit page 8.2W.
Trace offset 3.3V, 100mV/div Trace VIN1 falling through VTH(LO), 2V/div VO(MIN) 3.05V
2000 Semtech Corp.
www.semtech.com
SC1532
POWER MANAGEMENT Typical Characteristics (Cont.)
Transient Load Response(1)
Note: Application Circuit page
Trace offset 3.3V, 50mV/div Trace stepping from 400mA
Applications Information
Introduction SC1532 intended applications such power managed network interface cards (NICs), where operation from 3.3V VAUX supply required when supply been shut down. provides simple, cost solution that uses very little real estate. During regular operation, 3.3V power card provided SC1532s on-board dropout regulator, generated from supply. When supply removed 3.3V VAUX available, SC1532 connects this supply directly output using internal NMOS pass device. Component Selection Output capacitors Semtech recommends 4.7µF greater ceramic capacitor output best combination performance cost effectiveness. Increasing capacitance value improves transient response glitch performance. SC1532 very tolerant output capacitor value variations, fact combination capacitors with sufficient stability. This target easily using surface mount ceramic tantalum capacitors. Input capacitors Semtech recommends
2000 Semtech Corp. www.semtech.com
4.7µF ceramic capacitor both inputs. This allows device being some distance from bulk capacitance rail. Additionally, input droop load transients reduced, improving load transient response aiding smooth supply transitions. Tantalum capacitors should used. Charge pump capacitor Semtech recommends ceramic capacitor between GND. Thermal Considerations When operating from supply, power dissipation SC1532 approximately equal product output current input output voltage differential:
(VIN
absolute worst-case dissipation given
(VIN
SC1532
POWER MANAGEMENT Applications Information (Cont.)
Note that VIN2(MAX) IQ2(MAX) term does apply VIN2 supplied. Inserting VIN1 5.5V, 3.234V, 400mA, VIN2 3.6V, yields:
VIN2 visa-versa, supplies chatter
SOURCE HYST
Using this figure, calculate maximum thermal impedance allowable maintain 125°C ambient temperature 55°C:
general, this avoided minimizing supply trace lengths resistances. circumstances where source impedance causing supply chattering, increasing value VIN1 input capacitor should solve problem reducing instantaneous drop jump VIN1 supplies switched. Layout Considerations While layout linear devices generally critical switching application, careful attention detail will ensure reliable operation. Figure below sample layout. Attaching part (pins larger copper footprint will enable better heat transfer from device, especially PCBs where there internal ground power planes. Place input output capacitors close device optimal transient response.
(125
.936
This readily achievable using copper area conducting heat away from device (see Figure below). VIN1 Source Impedance order ensure seamless transitions between supplies with VIN1 rising falling, recommended that source impedance VIN1 less than 0.125W. This because output current switches from VIN1
Copper
Silk Screen
Figure Suggested layout based upon Application Circuit Page Notes: vias ground plane. Copper area pins thru recommended, area only shown. Connect ground plane with vias.
2000 Semtech Corp. www.semtech.com
SC1532
POWER MANAGEMENT Outline Drawing SO-8
JEDEC REF: MS-012AA
Minimum Land Pattern SO-8
Contact Information
Semtech Corporation Power Management Products Division Mitchell Rd., Newbury Park, 91320 Phone: (805)498-2111 (805)498-3804
2000 Semtech Corp.
www.semtech.com

400mA SmartLDOwith Internal Pass MOSFET Glitch-free transition be

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