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LTM4639 Arkusz danych(PDF) 13 Page - Linear Technology |
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LTM4639 Arkusz danych(HTML) 13 Page - Linear Technology |
13 / 28 page LTM4632 13 4632fc For more information www.linear.com/LTM4632 APPLICATIONS INFORMATION Application Note 77 provides a detailed explanation of multiphase operation. The input RMS ripple current can- cellation mathematical derivations are presented, and a graph is displayed representing the RMS ripple cur- rent reduction as a function of the number of interleaved phases. Figure 4 shows this graph. Channel 1 Output Voltage Tracking and Soft-Start The TRACK/SS pin provides a means to either soft-start the Channel 1 regulator or track it to a different power supply. A capacitor on the TRACK/SS pin will program the ramp rate of the channel 1 output voltage. An internal 1.2µA current source will charge up the external soft-start capacitor towards INTVCC voltage. When the TRACK/SS voltage is below 0.6V, it will take over the internal 0.6V reference voltage to control the output voltage. The total soft-start time can be calculated as: tSS = 0.6 • CSS 1.2µA where CSS is the capacitance on the TRACK/SS pin. Forced continuous mode are disabled during the soft- start process. Channel 1 output voltage tracking can also be programmed externally using the TRACK/SS pin. The output can be tracked up and down with another regulator. Figure 5 and Figure 6 show an example waveform and schematic of a Ratiometric tracking where the slave regulator’s output slew rate is proportional to the master’s. Since the slave regulator’s TRACK/SS is connected to the master’s output through a RTR(TOP)/RTR(BOT) resistor divider and its voltage used to regulate the slave output voltage when TRACK/SS voltage is below 0.6V, the slave output voltage and the master output voltage should sat- isfy the following equation during the start-up. VOUT(SL) • RFB(SL) RFB(SL) +60.4k = VOUT(MA) • RTR(BOT) RTR(TOP) +RTR(BOT) The RFB(SL) is the feedback resistor and the RTR(TOP)/ RTR(BOT) is the resistor divider on the TRACK/SS pin of the slave regulator, as shown in Figure 6. Following the upper equation, the master’s output slew rate (MR) and the slave’s output slew rate (SR) in Volts/ Time is determined by: MR SR = RFB(SL) RFB(SL) +60.4k RTR(BOT) RTR(TOP) +RTR(BOT) For example, VOUT(MA) = 1.5V, MR = 1.5V/1ms and VOUT(SL) = 1.2V, SR = 1.2V/1ms. From the equation, we could solve out that RTR(TOP) = 60.4k and RTR(BOT) = 40.2k is a good combination for the Ratiometric tracking. TIME SLAVE OUTPUT MASTER OUTPUT 4632 F05 Figure 5. Output Ratiometric Tracking Waveform The TRACK pins will have the 1.2µA current source on when a resistive divider is used to implement tracking on that specific channel. This will impose an offset on the TRACK pin input. Smaller values resistors with the same ratios as the resistor values calculated from the above equation can be used. For example, where the 60.4k is used then a 6.04k can be used to reduce the TRACK pin offset to a negligible value. The Coincident output tracking can be recognized as a special Ratiometric output tracking which the master’s output slew rate (MR) is the same as the slave’s output slew rate (SR), as waveform shown in Figure 7. |
Podobny numer części - LTM4639 |
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Podobny opis - LTM4639 |
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