DESCRIPTIO FEATURES APPLICATIO S. LT1641 Positive High Voltage Hot Swap Controller TYPICAL APPLICATIO

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1 FEATURES Allows Safe Board Insertion and Removal from a Live Backplane Controls Supply Voltage from 9V to 0V Programmable Analog Foldback Current Limiting High Side Drive for an External N-Channel Automatic Retry Capability User Programmable Supply Voltage Power-Up Rate Undervoltage Lockout Overvoltage Protection Available in -Lead SO Package APPLICATIO S U Hot Board Insertion Electronic Circuit Breaker Industrial High Side Switch/Circuit Breaker 4V/4V Industrial/Alarm Systems DESCRIPTIO LT141 Positive High Voltage Hot Swap Controller U The LT 141 is an -pin Hot Swap TM controller that allows a board to be safely inserted and removed from a live backplane. Using an external N-channel pass transistor, the board supply voltage can be ramped up at a programmable rate. A high side switch driver controls an N-channel gate for supply voltages ranging from 9V to 0V. The chip features a programmable analog foldback current limit circuit. If the chip remains in current limit for more than a programmable time, the N-channel pass transistor turns off and is optionally set to automatically restart after a time-out delay. The output indicates when the output voltage, sensed by the pin, is within tolerance. The pin provides programmable undervoltage lockout. The LT141-1/LT141- are recommended for new designs. The LT141 is available in the -lead SO package., LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATIO U 4V Input Voltage Automatic Restart Application V IN 4V SHORT PIN R1 49.9k R S 0.01Ω Q1 IRF530 R5 Ω D1 CMPZ 54B R3 59k C L V OUT nf *SMAT70A SENSE R7 4k R 3.4k LT141 R4 3.57k *DIODES, INC. C 0.µF 141 TA01 1

2 ABSOLUTE AXI U RATI GS (Note 1) W W W Supply Voltage ( )...0.3V to 0V Input Voltage (SENSE)...0.3V to 0V Input Voltage ()...0.3V to 44V Input Voltage (, )...0.3V to 0V Output Voltage ()...0.3V to 0V Output Voltage ()...0.3V to 0V Operating Temperature Range LT141CS... 0 C to 70 C LT141IS C to 5 C Storage Temperature Range... 5 C to 150 C Lead Temperature (Soldering, sec) C U U U W PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER LT141CS LT141IS TOP VIEW 7 5 SENSE S PACKAGE -LEAD PLASTIC SO T JMAX = 15 C, θ JA = 1 C/W NOT RECOMMENDED FOR NEW DESIGNS SEE LT141-1/LT141- S PART MARKING I Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: Consult LTC Marketing for parts specified with wider operating temperature ranges. DC ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 5 C. V cc = 4V SYMBOL PARAMETER CDITIS MIN TYP MAX UNITS Operating Range 9 0 V I CC Supply Current = 3V 5.5 ma V LKO Undervoltage Lockout V V H Pin High Voltage Threshold Low to High Transition V V L Pin Low Voltage Threshold High to Low Transition V V HST Pin Hysteresis Voltage 0 mv I IN Pin Input Current V = 1 µa V Pin Threshold Line Regulation 9V 0V 0.05 mv/v V SENSETRIP SENSE Pin Trip Voltage ( V SENSE ) V = 0V 1 17 mv V = 1V mv I UP Pin Pull-Up Current Charge Pump On, V = 7V 5 0 µa I DN Pin Pull-Down Current Any Fault Condition, V = V ma V External N-Channel Gate Drive V, =.V to 0V V = 0V to 0V 1 V I UP Pin Pull-Up Current V = 0V µa I Pin Pull-Down Current V = 1V µa V H Pin High Threshold Low to High Transition V V L Pin Low Threshold High to Low Transition V V HYST Pin Hysteresis 0 mv I IN Pin Input Current V = 1 µa V OL Output Low Voltage I O = ma 0.4 V I O = 4mA.5 V I OH Pin Leakage Current V = 0V µa

3 AC ELECTRICAL CHARACTERISTICS T A = 5 C, = 4V SYMBOL PARAMETER CDITIS MIN TYP MAX UNITS t PHL Low to Low Figures 1, µs t PLH High to High Figures 1, 1.7 µs t PHL Low to Low Figures 1, 3 3. µs t PLH High to High Figures 1, µs t PHLSENSE ( SENSE) High to Low Figures 1, µs 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 device pins are positive; all currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified. TYPICAL PERFOR A CE CHARACTERISTICS U W I CC (ma) I CC vs 5 C 5 C 45 C (V) 141 G01 I CC (ma) I CC vs Temperature 3.0 4V.5 4V G0 PIN LOW VOLTAGE THRESHOLD (V) Pin Low Voltage Threshold vs Temperature G03 PIN HIGH VOLTAGE THRESHOLD (V) Pin High Voltage Threshold vs Temperature Pin Hysteresis vs Temperature I Pull Up vs Temperature 1.0 PIN HYSTERESIS (V) I PULL UP (µa) G G G0 3

4 TYPICAL PERFOR A CE CHARACTERISTICS U W DRIVE (V ) (V) Gate Drive vs Temperature Gate Drive vs Temperature Pin Pull Up Current vs =.V DRIVE (V ) (V) T A = 5 C (V) PIN PULL UP CURRENT (µa) G G0 141 G09 PIN PULL UP CURRENT (µa) Pin Pull Up Current vs T A = 45 C T A = 0 C T A = 5 C T A = 5 C PIN HIGH VOLTAGE THRESHOLD (V) Pin High Voltage Threshold vs Temperature PIN LOW VOLTAGE THRESHOLD (V) Pin Low Voltage Threshold vs Temperature (V) G 141 G G1 PIN LOW VOLTAGE HYSTERESIS (V) Pin Voltage Hysteresis vs SENSE Pin Regulation Voltage vs Temperature V OUT Low vs I LOAD V FEEDBACK V OUT LOW (V) T A = 45 C T A = 5 C T A = 5 C I LOAD (ma) SENSE PIN REGULATI VOLTAGE (mv) T A = 5 C V FEEDBACK (V) 141 G G G15 4

5 PI FU CTIO S U U U (Pin 1): The pin is used to implement undervoltage lockout. When the pin is pulled below the 1.33V Highto-Low threshold voltage, an undervoltage condition is detected and the pin is pulled low to turn the MOSFET off. When the pin rises above the 1.313V Low-to-High threshold voltage, the MOSFET is turned on again. (Pin ): Power Good Comparator Input. It monitors the output voltage with an external resistive divider. When the voltage on the pin is lower than the High-to-Low threshold of 1.33V, the pin is pulled low and released when the pin is pulled above the 1.313V Lowto-High threshold. The pin also effects foldback current limit (see Figure 7 and related discussion). (Pin 3): Open Collector Output to. The pin is pulled low whenever the voltage at the pin falls below the High-to-Low threshold voltage. It goes into a high impedance state when the voltage on the pin exceeds the Low-to-High threshold voltage. An external pull-up resistor can pull the pin to a voltage higher or lower than. (Pin 4): Chip Ground. (Pin 5): Timing Input. An external timing capacitor at this pin programs the maximum time the part is allowed to remain in current limit. When the part goes into current limit, an 0µA pull-up current source starts to charge the timing capacitor. When the voltage on the pin reaches 1.33V, the pin is pulled low; the pull-up current will be turned off and the capacitor is discharged by a 3µA pull-down current. When the pin falls below 0.5V, the pin turns on once the pin is pulsed low. Use no less than 1.5nF for the timing capacitor, C. By connecting a 0.01µF capacitor from the pin to the center tap of a resistive divider at the pin, the part automatically restarts after a current limit fault. With a short at the output, the part cycles on and off with a 3.7 on-time duty cycle. (Pin ): The High Side Gate Drive for the External N-Channel. An internal charge pump guarantees at least V of gate drive for supply voltages above 0V and 4.5V gate drive for supply voltages between.v and 0V. The rising slope of the voltage at the is set by an external capacitor connected from the pin to and an internal µa pull-up current source from the charge pump output. When the current limit is reached, the pin voltage will be adjusted to maintain a constant voltage across the sense resistor while the timer capacitor starts to charge. If the pin voltage exceeds 1.33V, the pin will be pulled low. The pin is pulled to whenever the pin is pulled low, the supply voltage drops below the.3v undervoltage lockout threshold or the pin rises above 1.33V. SENSE (Pin 7): The Current Limit Sense Pin. A sense resistor must be placed in the supply path between and SENSE. The current limit circuit will regulate the voltage across the sense resistor ( V SENSE ) to 47mV when V is 0.5V or higher. If V drops below 0.5V, the voltage across the sense resistor decreases linearly and stops at 1mV when V is 0V. To defeat current limit, short the SENSE pin to the pin. (Pin ): The Positive Supply Input ranges from 9V to 0V for normal operation. I CC is typically ma. An internal undervoltage lockout circuit disables the chip for inputs less than.3v. 5

6 BLOCK DIAGRA W SENSE V P GEN V P REF GEN 1.33V 0.5V 1mV ~ 47mV 1.33V CHARGE PUMP AND DRIVER UNDERVOLTAGE LOCKOUT.3V 0.5V LOGIC V P 0µA 1.33V 3µA 141 BD TEST CIRCUIT 4V SENSE V 5V 5k nf 141 F01 Figure 1

7 TI I G DIAGRA S U W W 1.313V 1.33V 1.313V 1.33V t PLH t PHL t PLH t PHL 5V 1V 141 F0 1V 1V 141 F03 Figure. to Timing Figure 3. to Timing SENSE 47mV t PHLSENSE 141 F04 Figure 4. SENSE to Timing APPLICATIO S I FOR Hot Circuit Insertion ATIO U W U U When circuit boards are inserted into a live backplane, the supply bypass capacitors on the boards draw high peak currents from the backplane power bus as they charge up. The transient currents can permanently damage the connector pins and glitch the system supply, causing other boards in the system to reset. The LT141 is designed to turn on a board s supply voltage in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. The chip also provides undervoltage and overcurrent protection while a power good output signal indicates when the output supply voltage is ready. Power-Up Sequence The power supply on a board is controlled by placing an external N-channel pass transistor (Q1) in the power path (Figure 5). Resistor R S provides current detection and capacitor C1 provides control of the slew rate. Resistor R provides current control loop compensation while R5 prevents high frequency oscillations in Q1. Resistors R1 and R provide undervoltage sensing. After the power pins first make contact, transistor Q1 is turned off. If the voltage at the pin exceeds the turn-on threshold voltage, the voltage on the pin exceeds the undervoltage lockout threshold, and the voltage on the pin is less than 1.33V, transistor Q1 will be turned on (Figure ). The voltage at the pin rises with a slope equal to µa/c1 and the supply inrush current is set at I INRUSH = C L µa/c1. If the voltage across the current sense resistor R S gets too high, the inrush current will then be limited by the internal current limit circuitry which adjusts the voltage on the pin to maintain a constant voltage across the sense resistor. Once the voltage at the output has reached its final value, as sensed by resistors R3 and R4, the pin goes high. Short-Circuit Protection The LT141 features a programmable foldback current limit with an electronic circuit breaker that protects against short-circuits or excessive supply currents. The current limit is set by placing a sense resistor between (Pin ) and SENSE (Pin 7). 7

8 APPLICATIO S I FOR V IN 4V SHORT PIN R1 49.9k R S 0.05Ω Q1 IRF530 R5 Ω R, 1k, D1 CMPZ 54B C1 nf ATIO U W U U R3 59k C L V OUT R 3.4k 1 7 SENSE LT141 3 R4 3.57k R7 4k 5 4 C 0.µF 141 F05 Figure 5. Typical Application Figure. Power-Up Waveforms To prevent excessive power dissipation in the pass transistor and to prevent voltage spikes on the input supply during short-circuit conditions at the output, the current folds back as a function of the output voltage, which is sensed at the pin (Figure 7). When the voltage at the pin is 0V, the current limit circuit drives the pin to force a constant 1mV drop across the sense resistor. As the output voltage at the pin increases, the voltage across the sense resistor increases until the pin reaches 0.5V, at which point the voltage across the sense resistor is held constant at 47mV. The maximum current limit is calculated as: I LIMIT = 47mV/R SENSE For a 0.05Ω sense resistor, the current limit is set at 1.A and folds back to 40mA when the output is shorted to ground. The LT141 also features a variable overcurrent response time. The time required for the chip to regulate the pin (Pin ) voltage is a function of the voltage across the sense resistor connected between the pin (Pin ) and the SENSE pin (Pin 7). The larger the voltage, the faster the gate will be regulated. Figure shows the response time as a function of overdrive at the SENSE pin. The pin (Pin 5) provides a method for programming the maximum time the chip is allowed to operate in current limit. When the current limit circuitry is not active, the pin is pulled to by a 3µA current source. After the current limit circuit becomes active, an 0µA pullup current source is connected to the pin and the voltage will rise with a slope equal to 77µA/C as long as the current limit circuit remains active. Once the desired maximum current limit time is set, the capacitor value is: C(nF) = t(ms). If the current limit circuit turns off, the pin will be discharged to by the 3µA current source. Whenever the pin reaches 1.33V, the pin is immediately pulled to and the pin is pulled back to by the 3µA current source. The part is not allowed to turn on again until the voltage at the pin falls below 0.5V. The waveform in Figure 9 shows how the output turns off following a short-circuit. The drop across the sense resistor is held at 1mV as the timer ramps up. Since the output did not rise bringing above 0.5V, the circuit turns off.

9 APPLICATIO S I FOR V SENSE 47mV ATIO U W U U 1µs µs µs RESPSE TIME µs 1mV 4µs µs 0V 0.5V V 141 F07 Figure 7. Current Limit Sense Voltage vs Feedback Pin Voltage 50mV 0mV 150mV 00mV Figure. Response Time to Overcurrent V SENSE 141 F0 Automatic Restart To force the LT141 to automatically restart after an overcurrent fault, the bottom plate of capacitor C1 can be tied back to the pin (Figure ). When an overcurrent condition occurs, the pin is driven to maintain a constant voltage across the sense resistor. The capacitor C at the pin will begin to charge. When the voltage at the pin reaches 1.33V, the pin is immediately pulled to and transistor Q1 turns off. Capacitor C1 momentarily pulses the pin low and allows the part to turn off. When the voltage at the pin ramps back down to 0.5V, the LT141 turns on again. If the short-circuit condition at the output still exists, the cycle will repeat itself indefinitely with a 3.7 on-time duty cycle which prevents Q1 from overheating. The waveforms are shown in Figure 11. Undervoltage and Overvoltage Detection The pin can be used to detect an undervoltage condition at the power supply input. The pin is internally connected to an analog comparator with 0mV of hysteresis. If the pin falls below its threshold voltage (1.33V), the pin is pulled low and is held low until is high again. Figure 1 shows an overvoltage detection circuit. When the input voltage exceeds the Zener diode s breakdown voltage, D turns on and starts to pull the pin high. After the pin is pulled higher than 1.33V, the fault latch is set and the pin is pulled to immediately, turning off transistor Q1. The waveforms are shown in Figure 13. Operation is restored either by interrupting power or by pulsing low. Power Good Detection The LT141 includes a comparator for monitoring the output voltage. The noninverting input ( pin) is compared against an internal 1.33V precision reference and exhibits 0mV hysteresis. The comparator s output ( pin) is an open collector capable of operating from a pull-up as high as 0V. The pin can be used to directly enable/disable a power module with an active high enable input. Figure 14 shows how to use the pin to control an active low enable input power module. Signal inversion is accomplished by transistor Q and R7. Supply Transient Protection The LT141 is 0% tested and guaranteed to be safe from damage with supply voltages up to 0V. However, spikes above 0V may damage the part. During a shortcircuit condition, the large change in currents flowing through the power supply traces can cause inductive voltage spikes which could exceed 0V. To minimize the spikes, the power trace parasitic inductance should be minimized by using wider traces or heavier trace plating and a surge suppressor placed between and. 9

10 APPLICATIO S I FOR ATIO U W U U V IN 4V SHORT PIN R1 49.9k C1 nf R S 0.05Ω Q1 IRF530 R5 Ω D1 CMPZ 54B R3 59k C L V OUT R 3.4k 1 7 SENSE LT141 3 R4 3.57k R7 4k 5 4 C 0.µF 141 F Figure 9. Short-Circuit Waveforms Figure. Automatic Restart Application V IN 4V SHORT PIN R1 49.9k R 3.4k D 30V 1N55B 1 R S 0.05Ω Q1 IRF530 R5 Ω 7 SENSE LT141 R, 1k, D1 CMPZ 54B C1 nf 3 R3 59k R4 3.57k R7 4k C L V OUT 5 4 C 0.µF 141 F1 Figure 11. Automatic Restart Waveforms Figure 1. Overvoltage Detection Pin Voltage A curve of gate drive vs is shown in Figure 15. The pin is clamped to a maximum voltage of 1V above the input voltage. At minimum input supply voltage of 9V, the minimum gate drive voltage is 4.5V. When the input supply voltage is higher than 0V, the gate drive voltage is at least V and a regular N-FET can be used. In applications ranges 9V to 4V range, a logic level N-FET must be used with a proper protection Zener diode between its gate and source (as D1 shown is Figure 5).

11 APPLICATIO S I FOR Layout Considerations ATIO U W U U To achieve accurate current sensing, a Kelvin connection is recommended. The minimum trace width for 1oz copper foil is 0.0" per amp to make sure the trace stays at a reasonable temperature. 0.03" per amp or wider is recommended. Note that 1oz copper exhibits a sheet resistance of about 530µΩ/. Small resistances add up quickly in high current applications. To make the system immune to noise, the resistor divider to the pin needs to be close to the chip and keep traces to and short. A 0.1µF capacitor from the pin to also helps reject induced noise. Figure 1 shows a layout that addresses these issues. V IN 4V SHORT PIN R1 94k UV = 37V R.k 1 7 SENSE R S 0.01Ω Q1 IRF530 R5 Ω R, 1k, LT C 0.µF D1 CMPZ 54B C1 nf 3 R3 143k R4 4.k R7 47k Q MMBT5551LT1 C L 0µF ACTIVE LOW ENABLE MODULE V IN /OFF V IN V OUT V OUT 141 F14 V OUT Figure 13. Overvoltage Waveforms Figure 14. Active Low Enable Module 1 1 I LOAD V (V) 14 1 R1 VCC SENSE LT141 SENSE RESISTOR, R S 4 R (V) I LOAD 141 F F1 Figure 15. Gate Drive vs Supply Voltage Figure 1. Recommended Layout for R1, R and R S 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. 11

12 PACKAGE DESCRIPTIO U S Package -Lead Plastic Small Outline (Narrow.150 Inch) (Reference LTC DWG # ).050 BSC.045 ± ( ) NOTE MIN. ± ( ) (3. 3.9) NOTE ±.005 TYP RECOMMENDED SOLDER PAD LAYOUT ( ).0.00 ( ) 45 0 TYP ( ) ( ) ( ) NOTE: INCHES 1. DIMENSIS IN (MILLIMETERS) ( ) TYP. DRAWING NOT TO SCALE 3. THESE DIMENSIS DO NOT INCLUDE MOLD FLASH OR PROTRUSIS. MOLD FLASH OR PROTRUSIS SHALL NOT EXCEED.00" (0.15mm).050 (1.70) BSC SO 0303 RELATED PARTS PART NUMBER DESCRIPTI COMMENTS LT140A Negative High Voltage Hot Swap Controller Operates from V to 0V LTC141 Dual Channel Hot Swap Controller Operates Two Supplies from 3V to 1V and a Third to 1V LTC14 High Side Drive Hot Swap Controller in SO- System Reset Output with Programmable Delay LT141-1/LT141- Positive High Voltage Hot Swap Controller Pin Compatible for Latched Mode Operation/Automatic Retry LTC14 Fault Protected Hot Swap Controller Operates from 3V to 1.5V, Handles Surges to 33V LTC143 PCI Hot Swap Controller 3.3V, 5V, 1V, 1V Supplies for PCI Bus LT450 Negative 4V Hot Swap Controller Active Current Limiting for Supplies from 0V to 0V 1 LT/LWI 00 REV D PRINTED IN USA Linear Technology Corporation 130 McCarthy Blvd., Milpitas, CA (40) FAX: (40) LINEAR TECHNOLOGY CORPORATI 1999

TYPICAL APPLICATIO. LT1641-1/LT Positive High Voltage Hot Swap Controllers DESCRIPTIO FEATURES APPLICATIO S

TYPICAL APPLICATIO. LT1641-1/LT Positive High Voltage Hot Swap Controllers DESCRIPTIO FEATURES APPLICATIO S Positive High Voltage Hot Swap Controllers FEATURES Allows Safe Board Insertion and Removal from a Live Backplane Controls Supply Voltage from 9V to 0V Programmable Analog Foldback Current Limiting High