LTC4219 datasheet(14/16 Pages) LINER

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LTC4219

4219f

APPLICATIONS INFORMATION

The power good threshold using the internal resistive

divider on the FB pin matches the 10.5V requirement.

The ﬁnal schematic in Figure 5 results in very few external

components. The pull-up resistors, R1 and R3, connect

to the FLT and PG pins while the 20k (R2) converts the

IMON current to a voltage at a ratio:

VIMON = 20 µA/A

⎡⎣

⎤⎦ •20k •IOUT = 0.4 V/A

⎡⎣ ⎤⎦ •IOUT

In addition there is a 0.1μF bypass (C1) on the INTVCC pin.

Layout Considerations

In Hot Swap applications where load currents can be 5A,

narrow PCB tracks exhibit more resistance than wider tracks

and operate at elevated temperatures. The minimum trace

width for 1oz copper foil is 0.02" per amp to make sure

the trace stays at a reasonable temperature. Using 0.03"

per amp or wider is recommended. Note that 1oz copper

exhibits a sheet resistance of about 0.5m

Ω/square. Small

resistances add up quickly in high current applications.

There are two VDD pins on opposite sides of the package

that connect to the sense resistor and MOSFET. The PCB

layout should be balanced and symmetrical to each VDD

pin to balance current in the MOSFET bond wires. Figure 6

shows a recommended layout for the LTC4219.

Although the MOSFET is self protected from overtem-

perature, it is recommended to solder the backside of the

package to a copper trace to provide a good heat sink. Note

that the backside is connected to the SENSE pin and can-

not be soldered to the ground plane. During normal loads

the power dissipated in the package is as high as 1.9W. A

10mm

× 10mm area of 1oz copper should be sufﬁcient.

This area of copper can be divided in many layers.

It is also important to put C1, the bypass capacitor for

the INTVCC pin as close as possible between the INTVCC

and GND.

Figure 6. Recommended Layout

4217 F06

HEAT SINK

VIA TO

SINK

GND

OUT

VDD

0.1μF

RMON

20k

4219 F07

10k

100μF

VDD

EN1

EN2

OUT

GND

IMON

LTC4219DHC-5

INTVCC

TIMER

FLT

VOUT

ADC

Additional Applications

The LTC4219 has a wide operating range from 2.9V to 15V.

The PG threshold is set with an internal resistive divider.

All other functions are independent of supply voltage.

Figure 7 shows a 5V application with a PG threshold of

4.35V.

In addition to Hot Swap applications, the LTC4219 also

functions as a backplane resident switch for removable

load cards (see the Typical Application section).

Figure 7. 5V, 5A Card Resident Application

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