LTM4643 datasheet(13/32 Pages) LINER

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LTM4643

4643fb

For more information www.linear.com/LTM4643

APPLICATIONS INFORMATION

towards the INTVCC voltage. When the TRACK/SS voltage

is below 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 as:

tSS = 0.6 •

CSS

2.5µA

where CSS is the capacitance on the TRACK/SS pin. Cur-

rent foldback and forced continuous mode are disabled

during the soft-start process.

Outputvoltagetrackingcanalsobeprogrammedexternally

using the TRACK/SS pin of each regulator channel. The

output can be tracked up and down with another regula-

tor. Figure 3 and Figure 4 show an example waveform

and schematic of a ratiometric tracking where the slave

regulator’s (VOUT2, VOUT3 and VOUT4) output slew rate is

proportional to the master’s (VOUT1).

Since the slave regulator’s TRACK/SS is connected to

the master’s output through a RTR(TOP)/RTR(BOT) resistor

divider and its voltage used to regulate the slave output

4643 F04

CH1

CSS

0.1µF

RFB1

13.3k

VIN

5V TO 20V

RTR2(TOP)

60.4k

CH2

RFB2

19.1k

CH3

RFB3

30.1k

CH4

RFB4

60.4k

RTR2(BOT)

13.3k

RTR3(TOP)

60.4k

RTR3(BOT)

13.3k

RTR4(TOP)

60.4k

RTR4(BOT)

13.3k

4643 F03

TIME

VOUT4 = 1.2V

VOUT3 = 1.8V

VOUT2 = 2.5V

VOUT1 = 3.3V

Figure 3. Output Ratiometric Tracking Waveform

Figure 4. Output Ratiometric Tracking Schematic

voltage when TRACK/SS voltage is below 0.6V, the slave

outputvoltageandthemasteroutputvoltageshouldsatisfy

the following equation during the start-up.

VOUT(SL) •

RFB(SL)

RFB(SL) + 60.4k

= VOUT(MA) •

RTR(BOT)

RTR(TOP) +RTR(BOT)

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