LTM4614EVPBF datasheet(10/20 Pages) LINER

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LTM4614

4614fa

APPLICATIONS INFORMATION

Figure 2. Dual Outputs (1.5V and 1.2V) with Tracking

4614 F02

PGOOD1

VOUT1

FB1

COMP1

TRACK1

RUN/SS1

PGOOD2

VOUT2

FB2

COMP2

TRACK2

RUN/SS2

LTM4614

VIN1

VIN2

GND1

GND2

10k

RTB

4.99k

RFB2

5.76k

VIN OR

CONTROL

RAMP

22μF

6.3V

100μF

6.3V

100μF

6.3V

1.2V

1.5V

PGOOD1

10k

PGOOD2

22μF

6.3V

22μF

6.3V

22μF

6.3V

VIN 3V TO 5.5V

RFB1

10k

RTA

10k

1.5V

CSSEXT1

Fault Conditions: Current Limit and Overcurrent

Foldback

The LTM4614 has current mode control, which inher-

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

in steady-state operation, but also in transient.

Along with foldback current limiting in the event of an

overload condition, the LTM4614 has overtemperature

shutdown protection that inhibits switching operation

around 150°C for each channel.

Run Enable and Soft-Start

The RUN/SS pins provide a dual function of enable and

soft-start control for each channel. The RUN/SS pins are

used to control turn on of the LTM4614. While each enable

pin is below 0.5V, the LTM4614 will be in a low quiescent

current state. At least a 0.8V level applied to the enable

pins will turn on the LTM4614 regulators. This pin can be

used to sequence the regulator channels. The soft-start

control is provided by a 1M pull-up resistor (RSS) and a

1000pF capacitor (CSS) as drawn in the Block Diagram for

each channel. An external capacitor can be applied to the

RUN/SS pin to increase the soft-start time. A typical value

is 0.01μF. The approximate equation for soft-start:

SOFTSTART = In

IN – 1.8V

⎛

⎝⎜

⎞

⎠⎟

•R

SS •CSS

where RSS and CSS are shown in the Block Diagram of

Figure 1, and 1.8V is the soft-start upper range. 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 pins. Either output can be tracked up

or 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 to

implement coincident tracking. The LTM4614 uses a very

accurate 4.99k resistor for the internal top feedback resistor.

Figure 2 shows an example of coincident tracking.

Equations:

TRACK1

FB1

4.99k

FB1

⎛

⎝⎜

⎞

⎠⎟

• Master

Slave

= 1+

4.99k

FB1

⎛

⎝⎜

⎞

⎠⎟

• TRACK1

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