LTM4650 datasheet(20/38 Pages) AD

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LTM4652

Rev. 0

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APPLICATIONS INFORMATION

The RFB(SL) is the feedback resistor and the RTR(TOP)/

RTR(BOT) is the resistor divider on the TRACK pin of the

slave regulator, as shown in Figure 9.

Following Equation 7, the ratio of the master’s output

slew rate (MR) to the slave’s output slew rate (SR) is

determined by Equation 8.

RFB(SL)

RFB(SL)+60.4k

RTR(BOT)

RTR(TOP)+RTR(BOT)

(8)

For example, VOUT(MA)=1.5V, MR = 1.5V/1ms and VOUT(SL)

= 3.3V, SR = 3.3V/1ms. From Equation 8, we could solve

that RTR(TOP) = 60.4k and RTR(BOT) = 40.2k are a good

combination for the ratiometric tracking.

The TRACK pin will have the 1.25µA current source on

when a resistive divider is used to implement tracking

on the slave regulator. This will impose an offset on

the TRACK pin input. Smaller value resistors with the

same ratios as the resistor values calculated from the

Equation 8 can be used. For example, where the 60.4k is

used then a 6.04k can be used to reduce the TRACK pin

offset to a negligible value.

Coincident output tracking can be recognized as a special

ratiometric output tracking in which the master’s output

slew rate (MR) is the same as the slave’s output slew rate

(SR), waveform as shown in Figure 10.

From Equation 8, we could easily find that, in coinci-

dent tracking, the slave regulator’s TRACK pin resistor

divider is always the same as its feedback divider given

by Equation 9.

RFB(SL)

RFB(SL)+60.4k

RTR(BOT)

RTR(TOP)+RTR(BOT)

(9)

Figure 9. Example of Output Tracking Application Circuit

4652 F09

LTM4652

VIN

VINOVP

RUN1

RUN2

TEMP+

TEMP–

TRACK1

TRACK2

fSET

470µF

6.3V

RFB(SL)

13.3k

10k

100µF

6.3V

×3

PHASMD

VOUT1

VOUTS1

SW1

VFB1

VFB2

COMP1

COMP2

VOUTS2

VOUT2

SW2

PGOOD2

MODE_PLLIN CLKOUT INTVCC EXTVCC PGOOD1

PGOOD1

INTVCC

SGND

GND

VOUT1

(MASTER)

1.5V

RAMP TIME

tSOFTSTART = (CSS/1.25µA) • 0.6V

DIFFP

DIFFN DIFFOUT

40.2k

10k

4.7nF

PGOOD2

SLAVE

VOUT1

(MASTER)

1.5V

±25A

470µF

6.3V

100µF

6.3V

×3

10k

3.3nF

140k

RTR(TOP)

60.4k

4.5V TO 18V INTERMEDIATE BUS

845k

CSS

22µF

25V

RTR(BOT)

40.2k

22µF

25V

22µF

25V

22µF

25V

C10

4.7µF

10k

INTVCC

VOUT2

(SLAVE)

3.3V

±25A

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