LTM4601 datasheet(13/28 Pages) LINER

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LTM4601/LTM4601-1

4601f

APPLICATIO S I FOR ATIO

is frequency and m is the number of parallel phases. This

calculation process can be easily fulﬁlled using our Linear

Technology µModule Design Tool.

Fault Conditions: Current Limit and Overcurrent

Foldback

LTM4601 has a current mode controller, which inher-

ently limits the cycle-by-cycle inductor current not only

in steady-state operation, but also in transient.

To further limit current in the event of an overload condi-

tion, the LTM4601 provides foldback current limiting. If the

output voltage falls by more than 50%, then the maximum

output current is progressively lowered to about one sixth

of its full current limit value.

Soft-Start and Tracking

The TRACK/SS pin provides a means to either soft-start

the regulator or track it to a different power supply. A

capacitor on this pin will program the ramp rate of the

output voltage. A 1.5µA current source will charge up the

external soft-start capacitor to 80% of the 0.6V internal

voltage reference minus any margin delta. This will control

the ramp of the internal reference and the output voltage.

The total soft-start time can be calculated as:

V V

SOFTSTART

OUT MARGIN

()

.•

.–

•

()

When the RUN pin falls below 1.5V, then the SS pin is reset

to allow for proper soft-start control when the regulator

is enabled again. Current foldback and force continuous

mode are disabled during the soft-start process. The

soft-start function can also be used to control the output

ramp up time, so that another regulator can be easily

tracked to it.

Output Voltage Tracking

Output voltage tracking can be programmed externally

using the TRACK/SS pin. The output can be tracked up and

down with another regulator. The master regulator’s output

is divided down with an external resistor divider that is the

same as the slave regulator’s feedback divider. Figure 5

shows an example of coincident tracking. Ratiometric

modes of tracking can be achieved by selecting different

resistor values to change the output tracking ratio. The

master output must be greater than the slave output for

the tracking to work. Figure 6 shows the coincident output

tracking characteristics.

Figure 5

Figure 6

VOUT

VFB

MARG0

MARG1

VOUT_LCL

DIFFVOUT

VOSNS

–

PGOOD

MPGM

RUN

COMP

INTVCC

DRVCC

TRACK/SS

TRACK CONTROL

PLLIN

LTM4601

RSET

40.2k

100k

40.2k

MASTER

OUTPUT

60.4k

COUT

SLAVE OUTPUT

4601 F05

60.4k FROM

VOUT TO VFB

CIN

VIN

fSET

PGND

SGND

VIN

OUTPUT

VOLTAGE

TIME

4601 F06

MASTER OUTPUT

SLAVE OUTPUT

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