LTM4604 datasheet(10/20 Pages) LINER

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LTM4604

4604f

APPLICATIONS INFORMATION

VIN

PGOOD

COMP

LTM4604

RUN/SS

RFB3

1.62k

COUT1

μF

6.3V

×3

X5R OR

X7R

VMASTER

3.3V

CIN1

μF

6.3V

X5R OR X7R

CSSEXT

RAMP

CONTROL

OR VIN

VOUT

TRACK

GND

VIN

PGOOD

COMP

LTM4604

RUN/SS

RFB

5.76k

RFB2

5.76k

RFB1

4.99k

4604 F02

COUT2

μF

6.3V

×3

X5R OR

X7R

VSLAVE

1.5V

CIN2

μF

6.3V

X5R OR X7R

VOUT

TRACK

GND

Figure 2

TIME

MASTER OUTPUT

SLAVE OUTPUT

4604 F03

Figure 3

Run Enable and Soft-Start

The RUN/SS pin provides dual functions of enable and

soft-start control. The RUN/SS pin is used to control

turn on of the LTM4604. While this pin is below 0.5V, the

LTM4604 will be in a 7μA low quiescent current state. A

0.8V threshold will enable the LTM4604. This pin can be

used to sequence LTM4604 devices. The soft-start control

is provided by a 1M pull-up resistor (RSS) and a 1000pF

capacitor (CSS) as drawn in the Block Diagram. 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 is:

SOFTSTART

SSE

⎛

⎝⎜

⎞

⎠⎟

–.

•

()

where RSS and CSS are shown in the Block Diagram of

Figure 1, 1.8V is the soft-start upper range, and CSSEXT

is the additional capacitance for further soft-start contol.

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

output ramp-up time, so that another regulator can be

easily tracked. An independent ramp control signal can

be applied to the master ramp, otherwise, connect the

TRACK pin to VIN to disable tracking.

Output Voltage Tracking

Output voltage tracking can be programmed externally

using the TRACK 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

to implement coincident tracking. The LTM4604 uses a

very accurate 4.99k resistor for the top feedback resistor.

Figure 2 shows an example of coincident tracking.

TRACK

MASTER

499

•

VTRACK is the track ramp applied to the slave’s TRACK pin.

VTRACK applies the track reference for the slave output up

to the point of the programmed value at which VTRACK

proceeds beyond the 0.8V reference value. The VTRACK

pin must go beyond 0.8V to ensure the slave output has

reached its ﬁnal value. Load current must be present for

proper tracking.

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