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LTC4446 Datasheet(PDF) 10 Page - Linear Technology |
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LTC4446 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 18 page  LTC1154 10 1154fb APPLICATIONS INFORMATION The Y axis of the graph is normalized to one RC time constant. The X axis is normalized to the current. (The set current is defined as the current required to develop 100mV across the drain sense resistor). Note that the shutdown time is shorter for increasing levels of MOSFET current. This ensures that the total energy dissipated by the MOSFET is always within the bounds established by the manufacturer for safe operation. (See MOSFET data sheet for further information). Using a Speed-Up Diode To reduce the amount of time that the power MOSFET is in a short-circuit condition, “bypass” the delay resistor with a small signal diode as shown in Figure 6. The diode will engage when the drop across the drain sense resistor exceeds about 0.7V, providing a direct path to the sense pin and dramatically reducing the amount of time the MOSFET is in an overload condition. The drain sense resistor value is selected to limit the maximum DC current to 2.8A. The diode conducts when the drain current exceeds 20A and reduces the turn-off time to 15μs. Reverse Battery Protection The LTC1154 can be protected against reverse battery conditions by connecting a resistor in series with the ground lead as shown in Figure 7. The resistor limits the supply current to less than 50mA with –12V applied. Figure 6. Using a Speed-Up Diode IN EN STATUS GND VS DS G SD LTC1154 + 100μF IRF530 15V 12V 0.036Ω LTC1154 • F06 0.01μF 100k 1N4148 LOAD Since the LTC1154 draws very little current while in normal operation, the drop across the ground resistor is minimal. The 5V μP (or control logic) is protected by the 10k resis- tors in series with the input and status pins. Current Limited Power Supplies The LTC1154 requires at least 3.5V at the supply pin to ensure proper operation. It is therefore necessary that the supply to the LTC1154 be held higher than 3.5V at all times, even when the output of the switch is short circuited to ground. The output voltage of a current limited regulator may drop very quickly during short-circuit and pull the supply pin of the LTC1154 below 3.5V before the shutdown circuitry has had time to respond and remove drive from the gate of the power MOSFET. A supply filter should be Figure 7. Reverse Battery Protection Figure 8. Supply Filter for Current Limited Supplies IN EN STATUS GND VS DS G SD LTC1154 MTP12N06 15V 12V 0.05Ω LTC1154 • F07 LOAD 10k 300Ω 5V μP OR CONTROL LOGIC + 10μF 10k 10k 120k 5V 10k IN EN STATUS GND VS DS G SD LTC1154 0.1Ω IRLR024 SHORT- CIRCUIT 0.1μF 100k LTC1154 • F08 *20Ω + 47μF* + 10μF 1N4148 *SUPPLY FILTER COMPONENTS + 100μF 5V/2A REGULATOR >7V |
Similar Part No. - LTC4446 |
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Similar Description - LTC4446 |
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