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LTC1255 Datasheet(PDF) 9 Page - Linear Technology |
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LTC1255 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  9 LTC1255 APPLICATIO S I FOR ATIO VS DS1 1/2 LTC1255 G1 GND IN1 IRF530 12V 18V + 100 µF RSENSE 0.036 Ω LTC1255 • F06 CDELAY 0.01 µF R DELAY 100k 1N4148 LOAD Figure 6. Using a Speed-Up Diode The large output capacitors on many switching regula- tors, on the other hand, may be able to hold the supply pin of the LTC1255 above 3.5V sufficiently long that this extra filtering is not required. Because the LTC1255 is micropower in both the standby and ON state, the voltage drop across the supply filter is very small (typically < 6mV) and does not signifi- cantly alter the accuracy of the drain sense threshold voltage which is typically 100mV. AUTOMOTIVE APPLICATIONS Reverse Battery Protection The LTC1255 can be protected against reverse battery conditions by connecting a resistor in series with the ground lead as shown in Figure 8. The resistor limits the supply current to less than 120mA with – 12V applied. Since the LTC1255 draws very little current while in normal operation, the drop across the ground resistor is minimal. The 5V µP (or controlling logic) is protected by the 10k resistors in series with the input. Figure 7. Supply Filter for Current Limited Supplies VS DS1 1/2 LTC1255 G1 GND IN1 MTP12N06E 12V 14V + 10 µF RSENSE 0.036 Ω LTC1255 • F08 LOAD 100 Ω 28V 10k µp OR CONTROL LOGIC 5V Figure 8. Reverse Battery Protection Transient Overvoltage Protection A common scheme used to limit overvoltage transients on a 14V nominal automotive power bus is to clamp the supply to the module containing the high-side MOSFET switches with a large transient suppressor diode, D1 in Figure 9. This diode limits the supply voltage to 40V under worse case conditions. The LTC1255 is designed to survive short (10ms) 40V transients and return to normal operation after the transient has passed. Current Limited Power Supplies The LTC1255 requires at least 3.5V at the supply pin to ensure proper operation. It is therefore necessary that the supply to the LTC1255 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 LTC1255 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 added as shown in Figure 7 which holds the supply pin of the LTC1255 high long enough for the overcurrent shutdown cir- cuitry to respond and fully discharge the gate. Linear regulators with small output capacitors are the most difficult to protect as they can “switch” from a voltage mode to a current limited mode very quickly. VS DS1 1/2 LTC1255 G1 GND IN1 MTP12N06E 12V 15V + 10 µF RSENSE 0.1 Ω LTC1255 • F07 0.01 µF 100k 1N4148 10 Ω* + 47 µF* + 10 µF 12V/2A REGULATOR SHORT CIRCUIT *SUPPLY FILTER COMPONENT |
Similar Part No. - LTC1255_15 |
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Similar Description - LTC1255_15 |
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