LTC7860 - High Efficiency Switching Surge Stopper
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LTC7860 - High Efficiency Switching Surge Stopper - 1

LTC7860 High Efficiency Switching Surge Stopper Features High Efficiency VOUT Clamp Stops High Voltage Input Surges nn SWITCH-ON Mode 100% Duty Cycle for Normal Operation nn PROTECTIVE PWM Mode for Transients and Faults nn V Pin to SGND Range: 3.5V to 60V IN nn External Input Voltage is Extendable to 200V+ nn Adjustable Output Voltage Clamp nn Adjustable Output Overcurrent Protection nn Power Inductor Improves Input EMI in Normal Operation nn Programmable Fault Timer nn Adjustable Soft-Start for Input Inrush Current Limiting nn 4.5% Retry Duty Cycle During Faults nn Adjustable Switching Frequency: 50kHz to 850kHz nn Optional Reverse Input Voltage Protection nn Available in Thermally Enhanced 12-lead MSOP Package The LTC®7860 high efficiency surge stopper protects loads from high voltage transients. High efficiency permits higher currents and smaller solution sizes. During an input overvoltage event, such as a load dump in vehicles, the LTC7860 controls the gate of an external MOSFET to act as a switching DC/DC regulator (PROTECTIVE PWM mode). This operation regulates the output voltage to a safe level, allowing the loads to operate through the input over-voltage event. During normal operation (SWITCHON mode), the LTC7860 turns on the external MOSFET continuously, passing the input voltage through to the output. An internal comparator limits the voltage across the current sense resistor and regulates the maximum output current to protect against overcurrent faults. Applications Industrial and Automotive Power Telecom Power nn Vehicle Power Including ISO7637 nn Military Power Including MIL1275 nn nn L, LT, LTC, LTM, OPTI-LOOP, Linear Technology, Burst Mode 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. Protected by U.S. Patents including 5731694. An adjustable timer limits the time that the LTC7860 can spend in overvoltage or overcurrent regulation. When the timer expires, the external MOSFET is turned off until the LTC7860 restarts after a cool down period. By strictly limiting the time in PROTECTIVE PWM Mode when the power loss is high, the components and thermal design can be optimized for normal operation and safely operate through high voltage input surges and/or overcurrent faults. An additional PMOS can be added for reverse battery protection. PROTECTIVE PWM: VOUT Clamped to 18V During a VIN Surge

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LTC7860 - High Efficiency Switching Surge Stopper - 2

LTC7860 Absolute Maximum Ratings TOP VIEW TMR FREQ SGND SS VFB ITH GATE VIN SENSE CAP RUN VFBN MSE PACKAGE 12-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 40°C/W, θJC = 10°C/W EXPOSED PAD (PIN 13) IS PGND, MUST BE SOLDERED TO PCB Order Information LEAD FREE FINISH PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking,...

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LTC7860 - High Efficiency Switching Surge Stopper - 3

The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C. (Note 3) VIN = 12V, unless otherwise noted. SYMBOL Input Voltage Operating Range Undervoltage Lockout (VIN-VCAP) Ramping Up Threshold (VIN-VCAP) Ramping Down Threshold Hysteresis Input DC Supply Current Shutdown Supply Current Output Sensing VREG Regulated Feedback Voltage VREG = (VFB – VFBN) VITH = 1.2V (Note 4) Feedback Voltage Line Regulation Feedback Voltage Load Regulation VITH = 1.2V, ∆IITH = ±5µA (Note 4) Error Amplifier Transconductance...

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LTC7860 - High Efficiency Switching Surge Stopper - 4

The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C. (Note 3) VIN = 12V, unless otherwise noted. SYMBOL Programmable Switching Frequency RFREQ = 24.9kΩ RFREQ = 64.9kΩ RFREQ = 105kΩ High Switching Frequency Foldback Frequency as Percentage of Programmable Frequency Minimum On-Time Gate Driver VCAP Gate Bias LDO Output Voltage (VIN-VCAP) Gate Pull-Up Resistance Gate High Gate Pull-Down Resistance Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the...

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LTC7860 - High Efficiency Switching Surge Stopper - 5

LTC7860 Typical Performance Characteristics Frequency Over Input Voltage 600 FREQ = OPEN FREQUENCY FOLDBACK (%) GATE Bias LDO (VIN - VCAP) Load Regulation 0.1 Current Sense Voltage Over ITH Voltage TMR Pull-UP Current Over Temperature –25.0 SS Pin Pull-Up Current Over Temperature Current Sense Voltage Over Temperature CURRENT LIMIT SENSE VOLTAGE (mV) 100 CURRENT SENSE VOLTAGE (mV) GATE Bias LDO (VIN - VCAP) Dropout Behavior Frequency Foldback % Over Feedback Voltage Frequency Over Temperature TA = 25°C, unless otherwise noted.

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LTC7860 - High Efficiency Switching Surge Stopper - 6

LTC7860 Pin Functions TMR (Pin 1): Programmable Fault Timer. The TMR function monitors the time spent in PROTECTIVE PWM mode and provides fault control. During a fault, a 30μA (ITPU) current pulls up the TMR pin. If the fault clears before the 1.29V TMR Gate Off Threshold (VGTH) is reached, a 40μA current (ITPDR) resets the TMR pin to ground. The gate turns off and shuts down when VGTH is reached. In shutdown, a 1.3μA (ITPDC) current pulls TMR down to a 240mV TMR Restart Threshold (VRTH) allowing a cool down period before restart. FREQ (Pin 2): Switching Frequency Setpoint Input. The...

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LTC7860 - High Efficiency Switching Surge Stopper - 7

LTC7860 Pin Functions GATE (Pin 12): Gate Drive Output for External P-Channel MOSFET. The gate driver bias supply voltage (VIN-VCAP) is regulated to 8V when VIN is greater than 8V. The gate driver is disabled when (VIN-VCAP) is less than 3.5V (typical), 3.8V maximum in start-up and 3.25V (typical) 3.5V maximum in normal operation. PGND (Exposed Pad Pin 13): Ground Reference for Power Components (Power Ground). The PGND exposed pad must be soldered to the circuit board for electrical contact and for rated thermal performance of the package. Connect signal ground to power ground only at one...

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