Features n Reduces Power issipation by Replacing a Power Schottky iode with an N-Channel MOSFET n.5µs Turn-Off Time Limits Peak Fault Current n Wide Operating Voltage Range: 9V to 8V n Smooth Switchover without Oscillation n No Reverse C Current n Available in -Lead (mm 3mm) FN and 8-Lead MSOP Packages Applications n N + 1 Redundant Power Supplies n High Availability Systems n AdvancedTCA Systems n Telecom Infrastructure n Automotive Systems escription Positive High Voltage Ideal iode Controller The LTC 357 is a positive high voltage ideal diode controller that drives an external N-channel MOSFET to replace a Schottky diode. When used in diode-or and high current diode applications, the reduces power consumption, heat dissipation, voltage loss and PC board area. The easily ORs power sources to increase total system reliability. In diode-or applications, the controls the forward voltage drop across the MOSFET to ensure smooth current transfer from one path to the other without oscillation. If the power source fails or is shorted, a fast turn-off minimizes reverse current transients. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application, 1A iode-or Power issipation vs Load Current V A V TO LOA POWER ISSIPATION (W) 5 3 IOE (MBR11) POWER SAVE V B 1 FET () 8 CURRENT (A) 1 357 TA1b 357 TA1 *SEE FIGURES AN 3 FOR AITIONAL OPTIONAL COMPONENTS
Absolute Maximum Ratings Supply Voltages... 1V to 1V,....3V to 1V Output Voltage (Note 3)... V.V to V + 1V (Notes 1, ) Operating Ambient Temperature Range C... C to 7 C I... C to 85 C H... C to 15 C MP... 55 C to 15 C Storage Temperature Range... 5 C to 15 C Lead Temperature (Soldering, 1 sec) MS Package... 3 C pin Configuration TOP VIEW 1 3 7 NC CB PACKAGE -LEA (mm 3mm) PLASTIC FN T JMAX = 15 C, θ JA = 9 C/W EXPOSE PA (P 7) PCB CONNECTION OPTIONAL 5 NC NC 1 3 TOP VIEW 8 7 NC 5 MS8 PACKAGE 8-LEA PLASTIC MSOP T JMAX = 15 C, θ JA = 13 C/W ORER FORMATION LEA FREE FISH TAPE AN REEL PART MARKG* PACKAGE ESCRIPTION TEMPERATURE RANGE CMS8#PBF CMS8#TRPBF LTCX 8-Lead Plastic MSOP C to 7 C IMS8#PBF IMS8#TRPBF LTCX 8-Lead Plastic MSOP C to 85 C HMS8#PBF HMS8#TRPBF LTCX 8-Lead Plastic MSOP C to 15 C MPMS8#PBF MPMS8#TRPBF LTFWZ 8-Lead Plastic MSOP 55 C to 15 C LEA BASE FISH TAPE AN REEL PART MARKG* PACKAGE ESCRIPTION TEMPERATURE RANGE MPMS8 MPMS8#TR LTFWZ 8-Lead Plastic MSOP 55 C to 15 C LEA FREE FISH TAPE AN REEL (MI) TAPE AN REEL PART MARKG* PACKAGE ESCRIPTION TEMPERATURE RANGE CCB#TRMPBF CCB#TRPBF LCXF -Lead (mm 3mm) Plastic FN C to 7 C ICB#TRMPBF ICB#TRPBF LCXF -Lead (mm 3mm) Plastic FN C to 85 C HCB#TRMPBF HCB#TRPBF LCXF -Lead (mm 3mm) Plastic FN C to 15 C TRM = 5 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 5 C. V =, = 9V to 8V unless otherwise noted. SYMBOL PARAMETER CONITIONS M TYP MAX UNITS Operating Supply Range l 9 8 V I Supply Current l.5 1.5 ma I Pin Current V = V ±1V l 15 35 5 µa I Pin Current V = V ±1V l 8 1 µa V External N-Channel Gate rive (V V ), V = V to 8V, V = 9V to V I (UP) External N-Channel Gate Pull-Up Current V = V, V V =.1V l 1 µa I (OWN) External N-Channel Gate Pull-own Current in Fault Condition t OFF Gate Turn-Off Time V V = 55mV 1V, V V < 1V, C = pf V S Source-rain Regulation Voltage (V V ) l l V = V + 5V l 1 A 1.5 1 15 15 l 3 5 ns V V =.5V l 1 5 55 mv V V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note : All currents into pins are positive, all voltages are referenced to unless otherwise specified. Note 3: An internal clamp limits the pin to a minimum of 1V above or 1V above. riving this pin to voltages beyond this clamp may damage the device. Typical Performance Characteristics Current (I vs ) Current (I vs V ) Current (I vs V ) 8 18 = V = V ± 1V = V = V + 1V 3 = V = V 1V 15 1 = V = V + 1V I (µa) I (µa) I (µa) 9 1 3 = V = V 1V (V) 8 357 G1 V (V) 8 357 G V (V) 8 357 G3
Typical Performance Characteristics 5 Current vs Forward rop (I vs V S ) V =.5V 15 V vs Current (V vs I ) 15 Current (I vs V ) V = 1V, V = V > 18V 1 I (µa) 5 V (V) 1 5 V = 1V V = 9V I (µa) 75 5 5 5 5 5 V S (mv) 1 15 357 G 5 1 15 I (µa) 357 G5 5 8 1 1 1 V (V) 357 G 5 FET Turn-Off Time vs Capacitance V < V + 1V V S = 55mV 1V 3 FET Turn-Off Time vs Initial Overdrive V = V S = V ITIAL 1V t OFF (ns) 3 t P (ns) 1 1 C (nf) 8....8 1. V ITIAL (V) 357 G7 357 G8 t P (ns) 15 1 5 FET Turn-Off Time vs Final Overdrive V = V S = 55mV V FAL LOA CURRENT (A) FET Load Current vs VS 1 V = WITH FET () 8 1.8... V FAL (V) 5 5 V S (mv) 75 357 G1 357 G9
Pin Functions Exposed Pad: Exposed pad may be left open or connected to. : Gate rive Output. The pin pulls high, enhancing the N-channel MOSFET when the load current creates more than 5mV of voltage drop across the MOSFET. When the load current is small, the gate is actively driven to maintain 5mV across the MOSFET. If reverse current develops more than 5mV of voltage drop across the MOSFET, a fast pull-down circuit quickly connects the pin to the pin, turning off the MOSFET. + : evice Ground. : Input Voltage and Fast Pull-own Return. is the anode of the ideal diode and connects to the source of the N-channel MOSFET. The voltage sensed at this pin is used to control the source-drain voltage across the MOSFET. The fast pull-down current is returned through the pin. Connect this pin as close as possible to the MOSFET source. NC: No Connection. Not internally connected. : rain Voltage Sense. is the cathode of the ideal diode and the common output when multiple s are configured as an ideal diode-or. It connects to the drain of the N-channel MOSFET. The voltage sensed at this pin is used to control the source-drain voltage across the MOSFET. : Positive Supply Input. The is powered from the pin. Connect this pin to either directly or through an RC hold-up circuit. block diagram 17V CHARGE PUMP FP COMP + AMP + 5mV + 5mV 357 B
Operation High availability systems often employ parallel-connected power supplies or battery feeds to achieve redundancy and enhance system reliability. ORing diodes have been a popular means of connecting these supplies at the point of load. The disadvantage of this approach is the forward voltage drop and resulting efficiency loss. This drop reduces the available supply voltage and dissipates significant power. Using an N-channel MOSFET to replace a Schottky diode reduces the power dissipation and eliminates the need for costly heat sinks or large thermal layouts in high power applications. The controls an external N-channel MOSFET to form an ideal diode. The voltage across the source and drain is monitored by the and pins, and the pin drives the MOSFET to control its operation. In effect the MOSFET source and drain serve as the anode and cathode of an ideal diode. At power-up, the load current initially flows through the body diode of the MOSFET. The resulting high forward voltage is detected at the and pins, and the drives the pin to servo the forward drop to 5mV. If the load current causes more than 5mV of voltage drop when the MOSFET gate is driven fully on, the forward voltage is equal to R S(ON) I LOA. If the load current is reduced causing the forward drop to fall below 5mV, the MOSFET gate is driven lower by a weak pull-down in an attempt to maintain the drop at 5mV. If the load current reverses and the voltage across to is more negative than 5mV the responds by pulling the MOSFET gate low with a strong pull-down. In the event of a power supply failure, such as if the output of a fully loaded supply is suddenly shorted to ground, reverse current temporarily flows through the MOSFET that is on. This current is sourced from any load capacitance and from the other supplies. The quickly responds to this condition turning off the MOSFET in about 5ns, thus minimizing the disturbance to the output bus. Applications Information MOSFET Selection The drives an N-channel MOSFET to conduct the load current. The important features of the MOSFET are on-resistance, R S(ON), the maximum drain-source voltage, V SS, and the gate threshold voltage. Gate drive is compatible with.5v logic-level MOSFETs in low voltage applications ( = 9V to V). At higher voltages ( = V to 8V) standard 1V threshold MOS- FETs may be used. An internal clamp limits the gate drive to 15V between the and pins. An external Zener clamp may be added between and for MOSFETs with a V GS(MAX) of less than 15V. The maximum allowable drain-source voltage, BV SS, must be higher than the power supply voltage. If an input is connected to, the full supply voltage will appear across the MOSFET. ORing Two-Supply Outputs Where s are used to combine the outputs of two power supplies, the supply with the highest output voltage sources most or all of the load current. If this supply s output is quickly shorted to ground while delivering load current, the flow of current temporarily reverses and flows backwards through the s MOSFET. When the reverse current produces a voltage drop across the MOSFET of more than 5mV, the s fast pull-down activates and quickly turns off the MOSFET. If the other, initially lower, supply was not delivering load current at the time of the fault, the output falls until the body diode of its ORing MOSFET conducts. Meanwhile, the charges its MOSFET gate with µa until the forward drop is reduced to 5mV. If instead this supply was delivering load current at the time of the fault, its associated ORing MOSFET was already driven at least partially on, and the will simply drive the MOSFET gate harder in an effort to maintain a drop of 5mV.
Applications Information Load Sharing The application in Figure 1 combines the outputs of multiple, redundant supplies using a simple technique known as droop sharing. Load current is first taken from the highest output, with the low outputs contributing as the output voltage falls under increased loading. The 5mV regulation technique ensures smooth load sharing between outputs without oscillation. The degree of sharing is a function of R S(ON), the output impedance of the supplies and their initial output voltages. PSA PSB PSC V A RTNA V B RTNB V C RTNC M M3 357 F1 Figure 1. roop Sharing Redundant Supplies BUS Input Short-Circuit Faults The dynamic behavior of an active, ideal diode entering reverse bias is most accurately characterized by a delay followed by a period of reverse recovery. uring the delay phase some reverse current is built up, limited by parasitic resistances and inductances. uring the reverse recovery phase, energy stored in the parasitic inductances is transferred to other elements in the circuit. Current slew rates during reverse recovery may reach 1A/µs or higher. High slew rates coupled with parasitic inductances in series with the input and output paths may cause potentially destructive transients to appear at the and pins of the during reverse recovery. A zero impedance short-circuit directly across the input of the circuit is especially troublesome because it permits the highest possible reverse current to build up during the delay phase. When the MOSFET finally commutates the reverse current the pin experiences a negative voltage spike, while the pin spikes in the positive direction. To prevent damage to the under conditions of input short-circuit, protect the pin and pin as shown in Figure. The pin is protected by clamping to the pin in the negative direction. Protect the pin with a clamp, such as with a TVS or TransZorb, or with a local bypass capacitor of at least 1µF. In low voltage applications the MOSFET's drain-source breakdown may be sufficient to protect the pin, provided BV SS + V < 1V. Parasitic inductance between the load bypass and the allows a zero impedance input short to collapse the voltage at the pin, which increases the total turn-off time (t OFF ). For applications up to 3V, bypass the pin with 39µF; above 3V use at least 1µF. If is powered from the output side, one capacitor serves to guard against collapse and also protect from voltage spikes. If the pin is protected by a diode clamp or if is powered from the input side, decouple the pin with a separate 1Ω, 1nF filter (see Figure 3). In applications above 1A increase the filter capacitor to 1µF.
Applications Information V PUT PARASITIC UCTANCE + REVERSE RECOVERY CURRENT PUT PARASITIC UCTANCE + V PUT SHORT SBR1U- 15SA C 1µF OR CLAMP SMAT7A C LOA 357 F Figure. Reverse Recovery Produces Inductive Spikes at the and Pin. The Polarity of Step Recovery Spikes is Shown Across Parasitic Inductances V PUT PARASITIC UCTANCE V PUT SHORT R1 1Ω OR C C LOA 357 F3 C1 1nF Figure 3. Protecting Against Collapse of uring Reverse Recovery esign Example The following design example demonstrates the calculations involved for selecting components in a 1V system with 1A maximum load current (see Figure ). V 1 1V Si87Y R1 1Ω V TO LOA First, calculate the R S(ON) of the MOSFET to achieve the desired forward drop at full load. Assuming V ROP =.1V, R S(ON) V ROP =.1V I LOA 1A R S(ON) 1mΩ V 1V M Si87Y C1.1µF The Si87Y offers a good solution, in an S8 package with R S(ON) = 1mΩ(max) and BV SS of 3V. The maximum power dissipation in the MOSFET is: P = I LOA R S(ON) = (1A) 1mW = 1W 357 F R1 1Ω C1.1µF With less than 39µF of local bypass, the recommended RC values of 1W and.1µf were used in Figure. Figure. 1V, 1A iode-or Since BV SS + V is much less than 1V, output clamping is unnecessary.
Applications Information Layout Considerations Connect the and pins as close as possible to the MOSFET s source and drain pins. Keep the traces to the MOSFET wide and short to minimize resistive losses. See Figure 5. For the FN package, pin spacing may be a concern at voltages greater than 3V. Check creepage and clearance guidelines to determine if this is an issue. To increase the pin spacing between high voltage and ground pins, leave the exposed pad connection open. Use no-clean solder to minimize PCB contamination. V 1 3 S S S MOSFET 8 7 V V 1 3 S S S 8 7 V G 5 G 5 3 1 7 5 357 F5 Figure 5. Layout Considerations
Typical Applications Solar Panel Charging a Battery 1W SOLAR PANEL 1V SHUNT REGULATOR R1 1Ω + 1V BATTERY LOA C1.1µF 357 TA 1V Reverse Input Protection Reverse Input Protection V 1V Si87Y V 1V 1A C LOA V V 1A C LOA CLAMP SMAT7A 1 MMB15 357 TA3 1 MMB15 357 TA Low Current Shutdown V 5A R1 1Ω 1M FS37 V CLAMP SMAT7A C1.1µF 357 TA5 ON OFF G1 BSS13 1
Package escription CB Package -Lead Plastic FN (mm 3mm) (Reference LTC WG # 5-8-1715 Rev A).7.5..1 ( SIES) R =.115 TYP R =.5 TYP..1 3.55.5.15.5 1.5.5 ( SIES) PACKAGE LE.5.5.5 BSC 1.35.5 ( SIES) RECOMMENE SOLER PA PITCH AN IMENSIONS P 1 BAR TOP MARK (SEE NOTE ). REF 3..1 ( SIES).75.5..5 1.5.1 ( SIES) 3 1.35.1 ( SIES) 1.5.5.5 BSC BOTTOM VIEW EXPOSE PA P 1 NOTCH R. OR.5 5 CHAMFER (CB) FN 5 NOTE: 1. RAWG TO BE MAE A JEEC PACKAGE LE M-9 VARIATION OF (TB). RAWG NOT TO SCALE 3. ALL IMENSIONS ARE MILLIMETERS. IMENSIONS OF EXPOSE PA ON BOTTOM OF PACKAGE O NOT CLUE MOL FLASH. MOL FLASH, IF PRESENT, SHALL NOT EXCEE.15mm ON ANY SIE 5. EXPOSE PA SHALL BE SOLER PLATE. SHAE AREA IS ONLY A REFERENCE FOR P 1 LOCATION ON THE TOP AN BOTTOM OF PACKAGE 11
Package escription MS8 Package 8-Lead Plastic MSOP (Reference LTC WG # 5-8-1 Rev F) 3..1 (.118.) (NOTE 3) 8 7 5.5 (.5) REF 5.3 (.) M..38 (.15.15) TYP.889.17 (.35.5) 3. 3.5 (.1.13).5 (.5) BSC RECOMMENE SOLER PA LAY GAUGE PLANE.18 (.7).5 (.1) ETAIL A ETAIL A TYP.53.15 (.1.) NOTE: 1. IMENSIONS MILLIMETER/(CH). RAWG NOT TO SCALE 3. IMENSION OES NOT CLUE MOL FLASH, PROTRUSIONS OR BURRS. MOL FLASH, PROTRUSIONS OR BURRS SHALL NOT EXCEE.15mm (.") PER SIE. IMENSION OES NOT CLUE TERLEA FLASH OR PROTRUSIONS. TERLEA FLASH OR PROTRUSIONS SHALL NOT EXCEE.15mm (.") PER SIE 5. LEA COPLANARITY (BOTTOM OF LEAS AFTER FORMG) SHALL BE.1mm (.") MAX SEATG PLANE.9.15 (.193.) 1.1 (.3) MAX..38 (.9.15) TYP.5 (.5) BSC 1 3 3..1 (.118.) (NOTE ).8 (.3) REF.11.58 (..) MSOP (MS8) 37 REV F 1
Revision History (Revision history begins at Rev ) REV ATE ESCRIPTION PAGE NUMBER 9/1 Revised θ JA value for MS8 package in Pin Configuration section and added MP-grade to Order Information section Added two new plots and revised remaining curves in Typical Performance Characteristics section 3, Updated Electrical Characteristics section Revised Figure and Figure in Applications Information section 8 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 13
Typical Application Plug-In Card Input iode for Supply Hold-Up BACKPLANE CONNECTORS PLUG- CAR CONNECTOR 1 Hot Swap CONTROLLER V 1 + C HOLUP SMAT7A Hot Swap CONTROLLER V + C HOLUP SMAT7A PLUG- CAR CONNECTOR 357 TA Related Parts PART NUMBER ESCRIPTION COMMENTS LT11-1/LT11- Positive High Voltage Hot Swap Controllers Active Current Limiting, Supplies from 9V to 8V LTC191 ual Supply and Fuse Monitor UV/OV Monitor, 1V to 8V Operation, MSOP Package LT5 Hot Swap Controller Active Current Limiting, Supplies from 18V to 8V LTC51/LTC51-1/ LTC51- LTC5-1/LTC5-/ LTC5-1A/LTC5-A Hot Swap Controllers in SOT-3 Fast Active Current Limiting, Supplies from 15V Hot Swap Controllers in MS8/MS1 Fast Active Current Limiting, Supplies from 15V, rain Accelerated Response LTC53 Hot Swap Controller with Sequencer Fast Active Current Limiting, Supplies from 15V, rain Accelerated Response, Sequenced Power Good Outputs LT5 Positive Hot Swap Controller with Open-Circuit etect Foldback Current Limiting, Open-Circuit and Overcurrent Fault Output, Up to 8V Supply LTC Positive High Voltage Hot Swap Controller With I C and AC, Supplies from 8.5V to 8V LTC1 Negative High Voltage Hot Swap Controller With I C and 1-Bit AC, Adjustable Inrush and Overcurrent Limits LTC35 Ideal iode Controller with Monitor Controls N-Channel MOSFET, V to 18V Operation LTC35 LTC355 LT35-1/LT35-/ LT35-3 Negative Voltage iode-or Controller and Monitor Positive Voltage iode-or Controller and Monitor Surge Stopper, Overvoltage and Overcurrent Protection Regulator Controls Two N-Channel MOSFETs, 1µs Turn-Off, 8V Operation Controls Two N-Channel MOSFETs,.5µs Turn-Off, 8V Operation Wide Operation Range: V to 8V, Reverse Input Protection to V, Adjustable Output Clamp Voltage 1 LT 91 REV PRTE USA Linear Technology Corporation 13 McCarthy Blvd., Milpitas, CA 9535-717 (8) 3-19 l FAX: (8) 3-57 l www.linear.com LEAR TECHNOLOGY CORPORATION 7