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| SI4779CY New Product Vishay Siliconix High-Side N-Channel Switch with Current Limit FEATURES D D D D User Set Over Current Limit From 400 mA to 2.4 A Low rDS(on) 45 mW (max) at 25_C Fault Indicator Under Voltage Lockout APPLICATIONS D D D D D Notebook Computers Power Management USB Power Distribution Hot Plug In Power Supplies Power Supply/Load Protection Battery-Charger Circuits DESCRIPTION The SI4779CY n-channel high-side switch combines a low rDS(on) MOSFET switch with a user set, pulse gate control (PGC) based current limit. This switch is designed to protect the system power supply from overloads and short circuit conditions in applications such as USB. The PGC based approach to the current limiter provides the additional benefit of keeping the MOSFET junction temperature within specification, thereby eliminating the need for thermal shutdown. The low quiescent current makes the SI4779CY ideal for use in battery powered devices. The SI4779CY operates on both 3-V and 5-V busses, and is packaged in the LITTLE FOOTr SO-8 package. FUNCTIONAL BLOCK DIAGRAM IN OUT FAULT Control Circuit ON GND See page 7 for a detailed block diagram. Document Number: 71664 S-04276--Rev. A, 16-Jul-01 - SET VR www.vishay.com + 1 SI4779CY Vishay Siliconix New Product ABSOLUTE MAXIMUM RATINGS (TA = 25_C UNLESS OTHERWISE NOTED) Parameter Voltage, IN to GND Voltage, ON Continuous Drain Current (TJ = 150rC)a r Maximum Power Dissipationa Operating Junction and Storage Temperature Range TA = 25rC TA = 85rC TA = 70rC Symbol VIN VON ID PD Tj, Tstg Steady State -0.3 to 7 Unit V -0.3 to 7 2.4 2.4 0.65 -65 to 125 A W _C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. RECOMMENDED OPERATING CONDITIONS Parameter Voltage, IN to GND Voltage, ON or FAULT to GND Operating Temperature Range Symbol VIN VON, VFAULT TA Steady State 3.0 to 5.0 Unit V 0 to 5.0 0 to 85 _C THERMAL RESISTANCE RATINGS Parameter Junction-to-Ambienta Junction-to-Foot (Drain)b Steady State Symbol RthJA RthJF Typical 98 37 Maximum 120 46 Unit _C/W _ Notes a. Surface mounted on 1" x1" FR4 board, 0.062" thick, 2-oz copper double sided. b. Junction-to-foot thermal impedance represents the effective thermal impedance of all heat carrying leads in parallel and is intended for use in conjunction with the thermal impedance of the PC board pads to ambient (RthJA = RthJF + RthPCB-A). It can also be used to estimate chip temperature if power dissipation and the lead temperature of a heat carrying (drain) lead is known. www.vishay.com 2 Document Number: 71664 S-04276--Rev. A, 16-Jul-01 SI4779CY New Product SPECIFICATIONS Test Conditions Unless Specified Parameter Basic Operations Operating Voltage On-State Resistance VIN VIN = 4.75 V, ID = 2 A rDS(on) ISUP(off) Supply Current ON Input Low Voltage ON Input High Voltage ON Input Current ISUP(on) VONL VONH ION VIN = 3.0 V, ID = 2 A ON = IN, VIN = 5.5 V, VOUT = 0 V ON = GND, VIN = VOUT = 5.5 V, IOUT = 0 A VIN = 2.7 to 5.5 V VIN = 2.7 to 3.6 V VIN = 4.5 to 5.5 V VON = 5.5 V 2.0 2.4 0.01 "1 mA 2.7 0.035 0.045 5.5 0.045 0.055 2 70 0.8 V V W Vishay Siliconix Limits Min Typa Max Unit Symbol TA = 25_C, VIN = 5 V mA m Protection Over Current Limit Rangeb Under Voltage Lockout (falling edge) Under Voltage Hysteresis FAULT Output Voltage Lowb ILIMIT UVLO DUVLO VFAULT IFL ISINK = 100 mA VIN = VFAULT = 5.5 V 0.01 Tolerance = "20%, VIN = 5 V 0.4 2.0 2.3 0.1 0.4 1 mA 2.4 2.6 V A FAULT Logic Output Leakage Current Dynamicb Turn-On Time Rise Time Turn-Off Time Fall Time Cycle Time ton tr toff tf tcyc VIN = 5 V, IOUT = 500 mA VIN = 5 V, RL = 0.5 W VIN = 5 V, RL = 11 W CL = 40 m W, mF 3 ms 3.5 1.5 0.5 8 ms m ms Notes a. Typical values at TA = 25_C are for DESIGN AID ONLY, not guaranteed nor subject to production testing. b. Guaranteed by design. Derived from ISET current ratio, current-limit amplifier and external set resistor accuracy. TIMING DIAGRAMS ON 50% ON 50% ON ON 90% 50% OUT OUT 50% OUT 10% 90% OUT 10% ton FIGURE 1. Document Number: 71664 S-04276--Rev. A, 16-Jul-01 toff trise FIGURE 2. tfall www.vishay.com 3 SI4779CY Vishay Siliconix TIMING DIAGRAMS New Product ON VRSET ILIMIT tcyc FIGURE 3. TYPICAL CHARACTERISTICS (25_C UNLESS NOTED) RSET vs. ILIMIT 2.5 2.0 VIN = 5 V 1.5 I LIMIT (A) 1.0 0.5 RSET value is measured in circuit 0.0 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 RSET (W) Supply Current, Output Disalble vs. Ambient Temperature Over Operating Voltage 1000 r DS(on) - On-Resistance ( W) (Normalized) VIN = 5.5 V ON Input Current (nA) 1.4 Normalized On-Resistance vs. Ambient Temperature 1.2 100 1.0 0.8 10 0.6 1 -40 -20 0 20 40 60 80 100 0.4 -40 -25 -10 5 20 35 50 65 80 95 TA - Ambient Temperature (_C) TA - Ambient Temperature (_C) www.vishay.com 4 Document Number: 71664 S-04276--Rev. A, 16-Jul-01 SI4779CY New Product TYPICAL WAVEFORMS (VIN = 5 V, TA = 25_ UNLESS OTHERWISE NOTED) Vishay Siliconix 20 ms/div 1 ms/div CH1: CH2: CH3: IOUT, 2 A/div VOUT, 5 V/div, CL = 47 mF ON, 5 V/div CH1: CH2: CH3: IOUT, 0.5 A/div VOUT, 5 V/div, CL = 10 mF ON, 5 V/div FIGURE 4. Switch Turn-ON/OFF Time FIGURE 5. Switch Turn-ON Time 50 ms/div CH1: CH2: CH3: IOUT, 0.5 A/div VOUT, 5 V/div, CL = 10 mF ON, 5 V/div 200 ms/div CH1: CH2: CH3: IOUT, 0.5 A/div VOUT, 5 V/div, CL = 150 mF ON, 5 V/div NOTE: Discharge time based primarily on external R and C NOTE: Discharge time based primarily on external R and C FIGURE 6. Switch Turn-OFF Time FIGURE 7. Switch Turn-OFF Time Document Number: 71664 S-04276--Rev. A, 16-Jul-01 www.vishay.com 5 SI4779CY Vishay Siliconix New Product TYPICAL WAVEFORMS (VIN = 5 V, TA = 25_ UNLESS OTHERWISE NOTED) 2 ms/div 2 ms/div CH1: CH2: CH3: CH4: ON, 5 V/div VOUT, 5 V/div, RL = 0.5 W, CL = 47 mF FAULT, 5 V/div IOUT, 1 A/div CH1: CH2: CH3: CH4: ON, 5 V/div VRESET, 500 mV/div VOUT, 5 V/div, RL = 5.6 W, CL = 100 mF IOUT, 1 A/div FIGURE 8. FAULT to Short Response (tcyc) FIGURE 9. VRESET to Over Current Response 2 ms/div CH1: CH2: CH3: CH4: ON, 5 V/div PS Droops, 50 mV/div, Offset = 5 V VOUT, 1 V/div, RL = 0.5 W, CL = 100 mF IOUT, 0.5 A/div 2 ms/div CH1: CH2: CH3: CH4: ON, 5 V/div PS Droops, 100 mV/div, Offset = 5 V VOUT, 1 V/div, RL = 0.5 W, CL = 100 mF IOUT, 2 A/div NOTE: Special test with 820-mF capacitor at PS and RSET setup for 0.5 A. NOTE: Special test with 820-mF capacitor at PS and RSET setup for 2.4 A. FIGURE 10. Power Supply Droops vs. Short FIGURE 11. Power Supply Droops vs. Short www.vishay.com 6 Document Number: 71664 S-04276--Rev. A, 16-Jul-01 SI4779CY New Product PIN CONFIGURATION Vishay Siliconix PIN DESCRIPTION SO-8 IN IN ON ET 1 2 3 4 Top View 8 OUT OUT FAULT GND 3 4 5 6 7, 8 ON SET GND FAULT OUT Pin 1, 2 7 6 5 Symbol IN Description Input. N-channel MOSFET drain, bypass IN with a 100-mF capacitor to GND. Active-low switch-on input, logic low turns switch on. ON needs to be connected to VIN during power up, then connect to GND to activate the switch after power up. Current-limit input. A resistor from SET to GND sets the current limit for the switch. Ground Fault indicator output. This open drain output goes low when the circuit is in current limit or in short circuit protection mode. Switch output. N-channel MOSFET source. Si4778DY DETAILED BLOCK DIAGRAM 1 IN 8 OUT IN 2 7 OUT UVLO CP EA 3 ON QB S Q R + - 6 FAULT D + - 4 SET 5 GND RSET FIGURE 12. Document Number: 71664 S-04276--Rev. A, 16-Jul-01 www.vishay.com - BG + 7 SI4779CY Vishay Siliconix New Product DETAILED DESCRIPTION The SI4779CY limits the output current to a user-defined level. When the output current passes through the main switch a fraction of this current passes through a replica switch and RSET. RSET is an external sense resistor used to set the level of the over current limit; the over current limit should be set between 0.4 A and 2.4 A (see graph for RSET value vs. current limit). The circuit shuts down the switch when the current flowing through the switch exceeds Ilimit. After a short period of time, the circuit will slowly turn on the switch again. The length of time off is based on average power consumption, which is designed to be kept under 500 mW. If the output is shorted , the circuit will go into an on-off cycle to protect the switch and to prevent the battery from draining down. The fault output (FAULT) goes low when the circuit is in over current limit or short circuit protection mode. A 100-kW pull-up resistor from FAULT to IN provides a logic-control signal. APPLICATIONS DIAGRAM Line Input IN 100 mF 100 kW 100 kW FAULT OUT Line Output SI4779CY ON ON 100 mF 11 W SET RSET GND FIGURE 13. www.vishay.com 8 Document Number: 71664 S-04276--Rev. A, 16-Jul-01 |
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