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LT1640L Datasheet(PDF) 7 Page - Linear Technology |
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LT1640L Datasheet(HTML) 7 Page - Linear Technology |
7 / 16 page 7 LT1640L/LT1640H 1640lhfb APPLICATIONS INFORMATION Hot Circuit Insertion When circuit boards are inserted into a live – 48V backplane, the bypass capacitors at the input of the board’s power module or switching power supply can draw huge tran- sient currents as they charge up. The transient currents can cause permanent damage to the board’s components and cause glitches on the system power supply. The LT1640 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, overvoltage and overcurrent protection while keeping the power module off until its input voltage is stable and within tolerance. + VEE VDD LT1640H PWRGD UV = 37V OV = 71V SENSE C1 150nF 25V C3 0.1 µF 100V C4 100 µF 100V C5 100 µF 16V Q1 IRF530 R2 10 Ω 5% R3 18k 5% C2 3.3nF 100V R4 562k 1% R5 9.09k 1% R6 10k 1% R1 0.02 Ω 5% 4 3 2 OV GND GND – 48V UV 56 8 7 1 GATE DRAIN VICOR VI-J3D-CY VOUT + VOUT – VIN + 5V 1640 F06a GATE IN VIN – + (SHORT PIN) * * DIODES INC. SMAT70A 2 × 1N4148 4 3 2 1 Power Supply Ramping The input to the power module on a board is controlled by placing an external N-channel pass transistor (Q1) in the power path (Figure 6a, all waveforms are with respect to the VEE pin of the LT1640). R1 provides current fault detection and R2 prevents high frequency oscillations. Resistors R4, R5 and R6 provide undervoltage and over- voltage sensing. By ramping the gate of Q1 up at a slow rate, the surge current charging load capacitors C3 and C4 can be limited to a safe value when the board makes connection. Resistor R3 and capacitor C2 act as a feedback network to accurately control the inrush current. The inrush current can be calculated with the following equation: IINRUSH = (45µA • CL)/C2 where CL is the total load capacitance, C3 + C4 + module input capacitance. Figure 6a. Inrush Control Circuitry |
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