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LTC1255 Datasheet(PDF) 5 Page - Linear Technology |
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LTC1255 Datasheet(HTML) 5 Page - Linear Technology |
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5 / 16 page  5 LTC1255 PI FU CTIO S Input Pin The LTC1255 input pin is active high and activates all of the protection and charge pump circuitry when switched ON. The LTC1255 logic and shutdown inputs are high impedance CMOS gates with ESD protection diodes to ground and supply and therefore should not be forced beyond the power supply rails. The input pin should be held low during the application of power to properly set the input latch. Gate Drive Pin The gate drive pin is either driven to ground when the switch is turned OFF or driven above the supply rail when the switch is turned ON. This pin is of relatively high impedance when driven above the rail (the equiva- lent of a few hundred k Ω). Care should be taken to minimize any loading of this pin by parasitic resistance to ground or supply. Supply Pin The supply pin of the LTC1255 serves two vital pur- poses. The first is obvious; it powers the input, gate drive, regulation and protection circuitry. The second purpose is less obvious; it provides a Kelvin connection to the top of the drain sense resistor for the internal 100mV reference. The supply pin of the LTC1255 should never be forced below ground as this may result in permanent damage to the device. A 100 Ω resistor should be inserted in series with the ground pin if negative supply voltage transients are anticipated. The LTC1255 is designed to be continuously powered so that the gate of the MOSFET is actively driven at all times. If it is necessary to remove power from the supply pin and then reapply it, the input pin should be cycled (low to high) a few milliseconds after the power is reapplied to reset the input latch and protection circuitry. Also, the input pin should be isolated from the controlling logic by a 10k resistor if there is a possibility that the input pin will be held high after the supply has been removed. Drain Sense Pin The drain sense pin is compared against the supply pin voltage. If the voltage at this pin is more than 100mV below the supply pin, the input latch will be reset and the MOSFET gate will be quickly discharged. Cycle the input to reset the short-circuit latch and turn the MOSFET back on. This pin is also a high impedance CMOS gate with ESD protection and therefore should not be forced outside of the power supply rails. To defeat the overcurrent protection, short the drain sense pin to the supply pin. Some loads, such as large supply capacitors, lamps or motors require high in-rush currents. An RC time delay can be added between the sense resistor and the drain sense pin to ensure that the drain sense circuitry does not false trigger during startup. This time constant can be set from a few microseconds to many seconds. However, very long delays may put the MOSFET at risk of being destroyed by a short-circuit condition (see Applications Information section). OPERATIO The LTC1255 is a dual 24V MOSFET driver with built-in protection and gate charge pump. The LTC1255 consists of the following functional blocks: TTL and CMOS Compatible Inputs and Latches The LTC1255 inputs have been designed to accommo- date a wide range of logic families. Both input thresh- olds are set at about 1.3V with approximately 100mV of hysteresis. A low standby current regulator provides continuous bias for the TTL-to-CMOS converter. The input/protection latch should be set after initial power-up, or after reapplication of power, by cycling the input low to high. |
Similar Part No. - LTC1255_15 |
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Similar Description - LTC1255_15 |
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