LTM4643 datasheet(12/24 Pages) AD

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LTM4705

Rev. 0

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APPLICATIONS INFORMATION

Following Equation 9, the master’s output slew rate (MR)

and the slave’s output slew rate (SR) in Volts/Time is

determined by Equation 10.

RFB(SL)

RFB(SL) +60.4k

RTR(BOT)

RTR(TOP) +RTR(BOT)

(10)

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

VOUT(SL) = 1.2V, SR = 1.2V/1ms as shown in Figure 5.

From the equation, we could solve out that RTR(TOP) =

60.4k and RTR(BOT) = 40.2k is a good combination for the

Ratiometric tracking.

Figure 4. Output Ratiometric Tracking Waveform

Figure 6. Output Coincident Tracking Waveform

Figure 5. Example Schematic of Ratiometric

Output Voltage Tracking

TIME

SLAVE OUTPUT

MASTER OUTPUT

4705 F04

TIME

MASTER OUTPUT

SLAVE OUTPUT

4705 F06

0.1µF

40.2k

60.4k

VOUT1

40.2k

4705 F05

22µF

25V

VIN

3.1V TO 20V

VOUT1

1.5V, 5A

100µF

VOUT1

VOUT2

1.2V, 5A

100µF

VOUT2

FB1

COMP1

COMP2

GND

LTM4705

PGOOD1

PGOOD2

VIN2

VIN1

RUN1

RUN2

INTVCC

SYNC/MODE

TRACK/SS1

TRACK/SS2

FREQ

60.4k

FB2

The TRACK pins will have the 1.5µA current source on

when a resistive divider is used to implement tracking on

that specific channel. This will impose an offset on the

TRACK pin input. Smaller value resistors with the same

ratios as the resistor values calculated from the above

equation 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.

The Coincident output tracking can be recognized as a

special Ratiometric output tracking which the master’s

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

slew rate (SR), as waveform shown in Figure 6.

From Equation 10, we could easily find out that, in the

Coincident tracking, the slave regulator’s TRACK/SS pin

resistor divider is always the same as its feedback divider

(Equation 11).

RFB(SL)

RFB(SL) +60.4k

RTR(BOT)

RTR(TOP) +RTR(BOT)

(11)

For example, RTR(TOP) = 60.4k and RTR(BOT) = 60.4k is a

good combination for Coincident tracking for VOUT(MA) =

1.5V and VOUT(SL) = 1.2V application.

Power Good

The PGOOD pins are open drain pins that can be used to

monitor valid output voltage regulation. This pin monitors

a ±8% window around the regulation point. A resistor can

be pulled up to a particular supply voltage for monitoring.

To prevent unwanted PGOOD glitches during transients

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