Datasheet LTM4622 (Analog Devices) - 12
| Manufacturer | Analog Devices |
| Description | Dual Ultrathin 2.5A or Single 5A Step-Down DC/DC μModule Regulator |
| Pages / Page | 28 / 12 — APPLICATIONS INFORMATION. Soft-Start and Output Voltage Tracking. … |
| Revision | H |
| File Format / Size | PDF / 1.8 Mb |
| Document Language | English |
APPLICATIONS INFORMATION. Soft-Start and Output Voltage Tracking. Figure 2. Example of Clock Phasing for 4-Phase
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link to page 23 link to page 12 link to page 13 LTM4622
APPLICATIONS INFORMATION
133k, 1.5MHz
Soft-Start and Output Voltage Tracking
0° The TRACK/SS pin provides a means to either soft-start V+ 3.3V INTVCC SET SYNC/MODE VOUT1 10A PH 180° MOD the regulator or track it to a different power supply. A VOUT2 LTC6902 capacitor on the TRACK/SS pin will program the ramp 90° 0° DIV SYNC/MODE V OUT1 OUT1 rate of the output voltage. An internal 1.4µA current 90° 270° GND OUT2 VOUT2 source will charge up the external soft-start capacitor 4622 F02 towards INTVCC voltage. When the TRACK/SS voltage is
Figure 2. Example of Clock Phasing for 4-Phase
below 0.6V, it will take over the internal 0.6V reference
Operation with LTC6902
voltage to control the output voltage. The total soft-start The LTM4622 device is an inherently current mode con- time can be calculated as: trolled device, so parallel modules will have very good C t SS current sharing. This will balance the thermals on the SS = 0.6 • 1.4µA design. Please tie RUN, TRACK/SS, FB and COMP pin of each paralleling channel together. Figure 28 shows an where CSS is the capacitance on the TRACK/SS pin. example of parallel operation and pin connection. Current foldback and force continuous mode are disabled during the soft-start process.
INPUT RMS Ripple Current Cancellation
The LTM4622 has internal 400μs soft-start time when Application Note 77 provides a detailed explanation of TRACK/SS leave floating. multiphase operation. The input RMS ripple current can- cellation mathematical derivations are presented, and Output voltage tracking can also be programmed a graph is displayed representing the RMS ripple cur- externally using the TRACK/SS pin. The output can be rent reduction as a function of the number of interleaved tracked up and down with another regulator. Figure 4 and phases. Figure 3 shows this graph. 0.60 1-PHASE 2-PHASE 0.55 3-PHASE 4-PHASE 0.50 6-PHASE 0.45 0.40 0.35 0.30 0.25 DC LOAD CURRENT RMS INPUT RIPPLE CURRENT 0.20 0.15 0.10 0.05 00.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 DUTY FACTOR (VOUT/VIN) 4622 F03
Figure 3. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle
Rev. H 12 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Safety Considerations Layout Checklist/Example Package Description Revision History Package Photo Design Resources Related Parts
APPLICATIONS INFORMATION
133k, 1.5MHz
Soft-Start and Output Voltage Tracking
0° The TRACK/SS pin provides a means to either soft-start V+ 3.3V INTVCC SET SYNC/MODE VOUT1 10A PH 180° MOD the regulator or track it to a different power supply. A VOUT2 LTC6902 capacitor on the TRACK/SS pin will program the ramp 90° 0° DIV SYNC/MODE V OUT1 OUT1 rate of the output voltage. An internal 1.4µA current 90° 270° GND OUT2 VOUT2 source will charge up the external soft-start capacitor 4622 F02 towards INTVCC voltage. When the TRACK/SS voltage is
Figure 2. Example of Clock Phasing for 4-Phase
below 0.6V, it will take over the internal 0.6V reference
Operation with LTC6902
voltage to control the output voltage. The total soft-start The LTM4622 device is an inherently current mode con- time can be calculated as: trolled device, so parallel modules will have very good C t SS current sharing. This will balance the thermals on the SS = 0.6 • 1.4µA design. Please tie RUN, TRACK/SS, FB and COMP pin of each paralleling channel together. Figure 28 shows an where CSS is the capacitance on the TRACK/SS pin. example of parallel operation and pin connection. Current foldback and force continuous mode are disabled during the soft-start process.
INPUT RMS Ripple Current Cancellation
The LTM4622 has internal 400μs soft-start time when Application Note 77 provides a detailed explanation of TRACK/SS leave floating. multiphase operation. The input RMS ripple current can- cellation mathematical derivations are presented, and Output voltage tracking can also be programmed a graph is displayed representing the RMS ripple cur- externally using the TRACK/SS pin. The output can be rent reduction as a function of the number of interleaved tracked up and down with another regulator. Figure 4 and phases. Figure 3 shows this graph. 0.60 1-PHASE 2-PHASE 0.55 3-PHASE 4-PHASE 0.50 6-PHASE 0.45 0.40 0.35 0.30 0.25 DC LOAD CURRENT RMS INPUT RIPPLE CURRENT 0.20 0.15 0.10 0.05 00.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 DUTY FACTOR (VOUT/VIN) 4622 F03
Figure 3. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle
Rev. H 12 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Safety Considerations Layout Checklist/Example Package Description Revision History Package Photo Design Resources Related Parts