LTM4622 datasheet(13/28 Pages) LINER

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LTM4622

Rev F

For more information www.analog.com

APPLICATIONS INFORMATION

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

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

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

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

the slave regulator, as shown in Figure 5.

Following the upper equation, the master’s output slew

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

Time is determined by:

RFB(SL)

RFB(SL) + 60.4k

RTR(BOT)

RTR(TOP) + RTR(BOT)

For example, VOUT(MA) = 1.5V, MR = 1.4V/1ms and

VOUT(SL) = 1.2V, SR = 1.2V/1ms. 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.

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 values 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.

Figure 5. Example Schematic of Ratiometric

Output Voltage Tracking

Figure 6. Output Coincident Tracking Waveform

TIME

MASTER OUTPUT

SLAVE OUTPUT

4622 F06

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 the following equation during the start-up.

VOUT(SL) •

RFB(SL)

RFB(SL) + 60.4k

VOUT(MA) •

RTR(BOT)

RTR(TOP) + RTR(BOT)

Figure 4. Output Ratiometric Tracking Waveform

TIME

SLAVE OUTPUT

MASTER OUTPUT

4622 F04

40.2k

4622 F05

10µF

25V

VIN

4V TO 20V

VOUT1

1.5V, 2.5A

47µF

0.1µF

VOUT1

VOUT2

1.2V, 2.5A

47µF

VOUT2

FB1

COMP1

COMP2

FREQ

GND

LTM4622

PGOOD1 PGOOD2

VIN

RUN1

RUN2

INTVCC

SYNC/MODE

TRACK/SS1

TRACK/SS2

60.4k

40.2k

60.4k

FB2

VOUT1

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