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LTM4615EVPBF 数据表(PDF) 12 Page - Linear Technology |
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LTM4615EVPBF 数据表(HTML) 12 Page - Linear Technology |
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12 / 24 page  LTM4615 12 4615f APPLICATIONS INFORMATION Fault Conditions: Current Limit and Overcurrent Foldback The LTM4615 has current mode control, which inher- ently limits the cycle-by-cycle inductor current not only in steady-state operation, but also in transient. Along with foldback current limiting in the event of an overload condition, the LTM4615 has overtemperature shutdown protection that inhibits switching operation around 150°C for each channel. Run Enable and Soft-Start The RUN/SS pins provide a dual function of enable and soft-start control for each channel. The RUN/SS pins are used to control turn on of the LTM4615. While each enable pin is below 0.5V, the LTM4615 will be in a low quiescent current state. At least a 0.8V level applied to the enable pins will turn on the LTM4615 regulators. This pin can be used to sequence the regulator channels. The soft-start control is provided by a 1M pull-up resistor (RSS) and a 1000pF capacitor (CSS) as drawn in the block diagram for each channel. An external capacitor can be applied to the RUN/SS pin to increase the soft-start time. A typical value is 0.01μF. The approximate equation for soft-start: tIn VV RC SOFTSTART IN SS SS = ⎛ ⎝⎜ ⎞ ⎠⎟ VIN –. •• 18 where RSS and CSS are shown in the block diagram of Figure 1, and the 1.8V is soft-start upper range. The soft-start function can also be used to control the output ramp-up time, so that another regulator can be easily tracked to it. Output Voltage Tracking Output voltage tracking can be programmed externally using the TRACK pins. Either output can be tracked up or down with another regulator. The master regulator’s output is divided down with an external resistor divider that is the same as the slave regulator’s feedback divider to implement coincident tracking. The LTM4615 uses a very accurate 4.99k resistor for the internal top feedback resistor. Figure 2 shows an example of coincident tracking. Equations: TRACK R kR Master Slave FB FB 1 499 1 4 1 1 = + ⎛ ⎝⎜ ⎞ ⎠⎟ =+ . • .. • 99 1 1 k R TRACK FB ⎛ ⎝⎜ ⎞ ⎠⎟ PGOOD1 PGOOD1 FB1 COMP1 TRACK1 RUN/SS1 LDO_IN EN3 BOOST3 GND1 GND2 LTM4615 GND3 VIN1 VIN2 VOUT1 1.5V 1.2V VIN 3V TO 5.5V RFB1 10k R3 10k C4 22μF 6.3V C5 22μF 6.3V C7 22μF 6.3V C6 22μF 6.3V C8 22μF 6.3V C11 10μF 6.3V C13 CSSEXT C9 22μF 6.3V C3 22μF 6.3V C12 10μF C1 10μF 6.3V C2 10μF 6.3V C10 22μF 6.3V L1 0.2μH* SLAVE 1.2V 4A MASTER 1.5V 4A PGOOD2 PGOOD2 FB2 COMP2 TRACK2 VIN OR A CONTROL RAMP RUN/SS2 LDO_OUT FB3 PGOOD3 PGOOD3 VOUT2 RTA 10k *FAIR-RITE 0805 2508056007Y6 OPTIONAL FILTER RTB 4.99k RFB2 5.76k R6 10k 4615 F02 1V LOW NOISE 1V LOW NOISE AT 1A R5 3.32k R4 10k Figure 2. Dual Outputs (1.5V and 1.2V) with Tracking |
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