Datasheet LTM4668 (Analog Devices) - 10

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APPLICATIONS INFORMATION Multi-Channel Parallel Operation
A multiphase power supply significantly reduces the For the application that demands more than 1.2A of output amount of ripple current in both the input and output current, the LTM4668 multiple regulator channels can be capacitors. The RMS input ripple current is reduced by, easily paralleled to provide more output current without and the effective ripple frequency is multiplied by, the increasing input and output voltage ripples. The LTM4668 number of phases used (assuming that the input volt- has preset built-in 180° phase shift between channel 1, 2 age is greater than the number of phases used times and 3, 4 which is suitable to employ a 2+2, 3+1 or 4 chan- the output voltage). The output ripple amplitude is also nel parallel operation. Table 3 gives the phase difference reduced by the number of phases used when all of the between regulator channels. outputs are tied together to achieve a single high output current design.
Table 3. Phase Difference Between Regulator Channels CHANNEL
CH1 CH2 CH3 CH4 The LTM4668 device is an inherently current mode con- trolled device, so parallel modules will have very good
PHASE DIFF.
0° 180° 0° current sharing. This will balance the thermals on the design. When configuring the LTM4668 for parallel opera- Figure 1 shows a 2+2 and a 4-channels parallel concept tion, channels 1 and 4 serve as master channels to slave schematics for clock phasing. channels 2 and 3, respectively. To configure a channel as a slave, tie its FB pin to INTVCC to shut down its con- INTVCC INTVCC trol circuitry. The master channel’s drive signal is used instead to drive the slave channel’s power switches. Then, FB1 RUN1 FB2 RUN2 FB3 RUN3 FB4 RUN4 to complete configuration, tie its VOUT to the master chan- nel VOUT and its RUN pin to the master channel’s RUN pin. CH1 0° CH2 CH3 0° CH4 Channel 2 and 3 cannot be tied together to provide a dual (0°) (0°) (180°) (180°) channel single output. For a three-channel single-output, or four-channel single-output, channel 1 is used as the VOUT1 VOUT2 VOUT3 VOUT4 master channel. Table 4 lists the recommended channel LTM4668 combinations for multi-channel parallel operation. See Figure 18 and Figure 19 for paralleling operation. In paral- 2.4A 2.4A lel operation, use the master channel’s PGOOD signal as INTV INTV the power good indicator. Do not tie PGOOD pins together. CC INTVCC CC
Table 4. Configuration of Multi-Channel Parallel Operation
FB1 RUN1 FB2 RUN2 FB3 RUN3 FB4 RUN4
POWER NUMBER OF OUTPUT PARALLELING MASTER GOOD VOLTAGE RAILS CHANNEL CHANNEL INDICATOR
CH1 0° CH2 180° CH3 0° CH4 QUAD 1/2/3/4 (0°) (0°) (180°) (80°) TRIPLE 1+2/3/4 1 PGOOD1 DUAL 1+2/3+4 1, 4 PGOOD1,4 VOUT1 VOUT2 VOUT3 VOUT4 DUAL 1+2+4/3 1 PGOOD1 LTM4668 4668 F01 SINGLE 1+2+3+4 1 PGOOD1 4.8A
Input RMS Ripple Current Cancellation Figure 1. 2+2 and 4-Channel Parallel Concept Schematic
Application Note 77 provides a detailed explanation of multiphase operation. The input RMS ripple current can- cellation mathematical derivations are presented, and Rev. A 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Revision History Package Photo Design Resources Related Parts