LTM4705

11

Rev. 0

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APPLICATIONS INFORMATION

Figure 3. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle

a graph is displayed representing the RMS ripple cur-

rent reduction as a function of the number of interleaved

phases. Figure 3 shows this graph.

Soft-Start and Output Voltage Tracking

The TRACK/SS pin provides a means to either soft-start

the regulator or track it to a different power supply. A

capacitor on the TRACK/SS pin will program the ramp rate

of the output voltage. An internal 1.4µA current source

will charge up the external soft-start capacitor towards

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 by Equation 8.

1.4µA

(8)

Current foldback and force continuous mode are disabled

during the soft-start process.

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 4 and

Figure 5 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

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 Equation 9 during the start-up.

=

(9)

the slave regulator, as shown in Figure 5.

0.75 0.8

4705 F03

0.7

0.65

0.6

0.55

0.5

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.85 0.9

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

1-PHASE

2-PHASE

3-PHASE

4-PHASE

6-PHASE