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LT1312 Datasheet(PDF) 8 Page - Linear Technology |
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LT1312 Datasheet(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LT1312 APPLICATIONS INFORMATION on this line that may damage sensitive PCMCIA flash memory cards if applied directly to the VPP pins. Flash Memory Card VPP Power Considerations PCMCIA compatible flash memory cards require tight regulation of the 12V VPP programming supply to ensure that the internal flash memory circuits are never subjected to damaging conditions. Flash memory circuits are typi- cally rated with an absolute maximum of 13.5V and VPP must be maintained at 12V ±5% under all possible load conditions during erase and program cycles. Undervoltage can decrease specified flash memory reliability and over- voltage can damage the device 1. Generating 14V from 5V or 12V It is important that the 12V VPP supply for the two VPP lines to the card be free of voltage spikes. There should be little or no overshoot during transitions to and from the 12V level. inductor as shown in Figure 3. MOSFET Q4 and diode D4 have been added and diode D1 is no longer used. In the previous circuit, power is drawn directly from the batteries through D1, when the LTC1142 is in Burst Mode operation and the VPP pin requires 3.3V or 5V. For these lower input voltages this technique is no longer valid as the input will fall below the LT1312 regulator’s dropout voltage. To correct for this situation, the additional switch Q4 forces the switching regulator into continuous mode operation whenever 3.3V, 5V or 12V is selected. LINE POWERED SUPPLIES In line operated products such as: desktop computers, dedicated PC card readers/writers, medical equipment, test and measurement equipment, etc., it is possible to derive power from a relatively “raw” source such as a 5V or 12V power supply. The 12V supply line in a desktop computer however, is usually too “dirty” to apply directly to the VPP pins of a PCMCIA card socket. Power supply switching and load transients may create voltage spikes 1See Application Note AP-357, “Power Supply Solutions for Flash Memory,” Intel Corporation, 1992. D2 MBRS1100 D3 MBRS130T3 Q3 VN7002 VIN 5.4V TO 12V C4 1000pF C2 1000pF C3 220µF C1 68µF C5 22µF 3.3V OUTPUT FROM CARD VCC PIN Q1 24 23 6 1 28 EN0 EN1 VALID *LPE-6582-A086 DALE (605) 665-9301 14V AUXILIARY SUPPLY T1 3.38T 22µH* Q2 R4 22 Ω R1 100 Ω R3 18k R2 100 Ω R4 0.033 Ω D4 18V LT1312 F3 + Q4 VN7002 + + + VS EN0 TO CARD VPP PIN 0V, 3.3V, 5V, 12V OR Hi-Z VPPOUT LT1312 EN1 VALID SENSE GND 1µF 1/2 LTC1142 3.3V REG VIN PDRIVE NDRIVE SENSE+ SENSE– Figure 3. Deriving Auxiliary 14V Power from an LTC1142 3.3V Regulator |
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