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LTM4630 Datasheet(PDF) 11 Page - Linear Technology |
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LTM4630 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 28 page  LTM4632 11 4632fc For more information www.linear.com/LTM4632 APPLICATIONS INFORMATION Force Continuous Current Mode (CCM) Operation In applications where fixed frequency operation is more critical than low current efficiency, and where the low- est output ripple is desired, forced continuous opera- tion should be used. Forced continuous operation can be enabled by tying the SYNC/MODE pin to GND. In this mode, inductor current is allowed to reverse during low output loads, the COMP voltage is in control of the current comparator threshold throughout, and the top MOSFET always turns on with each oscillator pulse. During start- up, forced continuous mode is disabled and inductor current is prevented from reversing until the LTM4632’s output voltage is in regulation. Operating Frequency The operating frequency of the LTM4632 is optimized to achieve the compact package size and the minimum output ripple voltage while still keeping high efficiency. The default operating frequency is internally set to 1MHz. In most appli- cations, no additional frequency adjusting is required. Frequency Synchronization The power module has a phase-locked loop comprised of an internal voltage controlled oscillator and a phase detector. This allows the internal top MOSFET turn-on to be locked to the rising edge of the external clock. The external clock frequency range must be within ±30% around the set operating frequency. A pulse detection circuit is used to detect a clock on the SYNC/MODE pin to turn on the phase locked loop. The pulse width of the clock has to be at least 100ns. The clock high level must be above 2V and clock low level below 0.3V. The presence of an external clock will place both regulator channels into forced continuous mode operation. During the start-up of the regulator, the phase-locked loop function is disabled. Multiphase Operation (Configured as Multiphase Single Output VTT) For VTT termination output loads that demand more than 3A of current, two outputs in the LTM4632 or even mul- tiple LTM4632s can be paralleled to run out of phase to provide a multiphase single output VTT termination supply capable of souring and sinking higher current. 33.2k 3.3 INTVCC V+ PH MOD VOUT1 VOUT2 OUT1 0° 0° 90° 270° 4632 F02 180° VTT 12A 90° OUT2 SET SYNC/ MODE VOUT1 VOUT2 SYNC/ MODE DIV GND LTC6902 LTM4632 LTM4632 Figure 2. Example of Clock Phasing for 4-Phase Single Output VTT Operation with LTC6902 The two switching mode regulator channels inside the LTM4632 are internally set to operate 180° out of phase. Multiple LTM4632s could easily operate 90 degrees, 60 degrees or 45 degrees shift which corresponds to 4-phase, 6-phase or 8-phase operation by letting SYNC/ MODE of the LTM4632 synchronize to an external multi- phase oscillator like LTC6902. Figure 2 shows a 4-phase single output VTT termination supply design example for clock phasing. Tie FB1 pin of the LTM4632 to its INTVCC pin to put the module into two phase single VTT output operation mode. This will internally switch the Channel 1 error amplifier reference voltage from 0.6V to VTTR voltage, which is the same as Channel 2. Repeat this for each LTM4632 module in multiple LTM4632s paralleling application. Also tie RUN, TRACK/SS and COMP pin of each paral- leling channel together. Figure 20 shows an example of paralleled multiphase single output VTT termination sup- ply operation and pin connection. The LTM4632 device is an inherently current mode con- trolled device, so parallel modules will have very good cur- rent sharing. This will balance the thermals on the design. Multiphase Operation (Configured as VDDQ+VTT) For application which both VDDQ and VTT termination output loads demand more than 3A of current, two or multiple Channel 1 outputs from different LTM4632 mod- ules can be easily paralleled to provide a multiphase sin- gle VDDQ output while Channel 2 outputs from different LTM4632 modules can paralleled to provide a multiphase single VTT output. |
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