LTM4608 datasheet(15/24 Pages) LINER

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LTM4608

4608f

APPLICATIONS INFORMATION

same as the slave regulator’s feedback divider to implement

coincident tracking. The LTM4608 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. RFB4 in Figure

5 will be equal to RFB2 for coincident tracking.

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

LTM4608

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

4608 F05

100μF

POSCAP

SLAVE

1.5V

3.3V

LTM4608

SGND

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

TIME

MASTER OUTPUT

SLAVE OUTPUT

4608 F06

Figure 6

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

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