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LTM4608A

4608afa

APPLICATIONS INFORMATION

same as the slave regulator’s feedback divider to implement

coincident tracking. The LTM4608A uses an accurate 10k

resistor internally for the top feedback resistor. Figure 5

shows an example of coincident tracking:

Slave

= 1+

10k

RFB4

•VTRACK

VTRACK is the track ramp applied to the slave’s track

pin. VTRACK has a control range of 0V to 0.596V, or the

internal reference voltage. When the master’s output is

divided down with the same resistor values used to set

the slave’s output, this resistor divider is connected to

the slave’s track pin. The slave will then coincident track

with the master until it reaches its ﬁnal value. The master

will continue to its ﬁnal value from the slave’s regulation

point. Voltage tracking is disabled when VTRACK is more

than 0.596V.

VIN

SVIN

RUN

PLLLPF

TRACK

MODE

PHMODE

VOUT

ITH

ITHM

PGOOD

BSEL

MGN

CLKOUT GND

CLKIN

RUN

TRACK

RSR

CSR

100pF

22pF

RFB1

2.21k

100μF

MASTER

3.3V

VIN

TIE TO VIN

FOR DISABLE

AND DEFAULT

100μs SOFT-START

APPLY A CONTROL

RAMP WITH RSR AND

CSR TIED TO VIN WHERE

t = –(ln (1 – 0.596/VIN) • RSR • CSR)

OR APPLY AN EXTERNAL TRACKING RAMP

LTM4608A

SGND

VIN

SVIN

RUN

PLLLPF

TRACK

MODE

PHMODE

VOUT

ITH

ITHM

PGOOD

BSEL

MGN

CLKOUT GND

CLKIN

RUN

MASTER

3.3V

RFB2

6.65k

RFB3

10k

RFB4

6.65k

4608A F05

100μF

SLAVE

1.5V

3.3V

LTM4608A

SGND

Figure 5. Dual Outputs (3.3V and 1.5V) with Tracking

TIME

MASTER OUTPUT

SLAVE OUTPUT

4608A F06

Figure 6. Output Voltage Coincident Tracking

The track pin of the master can be controlled by an external

ramp or by RSR and CSR in Figure 5 referenced to VIN. The

RC ramp time can be programmed using equation:

= –ln 1–

0.596V

VIN

•RSR •CSR

LTM4608AV Datasheet(PDF) 15 Page - Linear Technology

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