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LT3582-12 Datasheet(PDF) 15 Page - Linear Technology |
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LT3582-12 Datasheet(HTML) 15 Page - Linear Technology |
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15 / 28 page  LT3582/LT3582-5/LT3582-12 15 3582512fb several start-up issues have occurred: A) the expected VOUTP ramp up path is not followed B) inductor current ringing occurs C) the VOUTP ramp rate is limited due to the output disconnect current limit being reached D) ad- ditional ringing occurs when the CAPP pin starts charging E) output voltage overshoot occurs because the inductor currents are maximized during the output ramp-up. In some cases it may be desirable to use only one RAMP pin capacitor. In cases where PUSEQ = 11 (see the Power- Up Sequencing section) the RAMPP and RAMPN pins can be connected together and to a single capacitor. In this case the capacitor will charge with twice the current configured by the IRMP bits. Ramping VOUTP from Ground: The LT3582 series has the unique ability to generate a smooth VOUTP voltage ramp starting from ground and continuing all the way up to regulation (see Figure 6). This ability is not possible with typical Boost converters in which the output is taken from the cathode of the Schottky diode (CAPP node in Figure 5). L1 D1 SWP C1 VOUTP C3 VIN C2 CAPP LT3582 SERIES DISCONNECT CONTROL LOAD 3582512 F05 APPLICATIONS INFORMATION The LT3582 series incorporates an output disconnect PMOS allowing VOUTP to be grounded during shutdown. Once enabled, the Disconnect Control circuit actively drives the PMOS gate allowing VOUTP to ramp up linearly as shown in Figure 6. Once VOUTP reaches regulation, the PMOS is fully turned “on” to reduce resistance and improve efficiency. Power-Up Sequencing (PUSEQ bits) Once enabled, the part requires a delay of TSTART-UP (64μs typ) to properly configure itself. Once configured, the order in which VOUTP and VOUTN ramp to regulation is controlled by the PUSEQ bits. The combinations available for the LT3582 are shown in Table 2. The LT3582-5/LT3582-12 are pre-configured with the 11 combination. Table 2. Power-Up Sequences PUSEQ[1:0] Power-Up Sequence 00 Outputs are disabled, neither output ramps up 01 VOUTN ramps up 1st, followed by VOUTP 10 VOUTP ramps up 1st, followed by VOUTN 11 Both VOUTP and VOUTN ramp-up starting at the same time. Selecting the 01 or 10 combinations cause one of the out- puts to start ramping shortly after SHDN rises. The ramp rate of VOUT is controlled by the RAMP pin as discussed in the Soft-Start section. After VOUT nears its target regula- Figure 5. Boost Converter Topology Figure 6. VOUTP Soft-Start Ramping from Ground Figure 7. VOUTP Soft-Start with Excessive Ramp Rate 3582512 F06 CAPP 2V/DIV IL2 0.2A/DIV VRAMPP 0.2V/DIV VOUTP 2V/DIV 1ms/DIV 3582512 F07 VOUTP 3V/DIV VRAMPP 0.5V/DIV CAPP 3V/DIV IL2 0.2A/DIV 50μs/DIV A C E BD |
Similar Part No. - LT3582-12_15 |
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Similar Description - LT3582-12_15 |
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