LTC4219
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 R4, connect
to the FLT and PG pins while the 20k (RMON) 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 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 0.5mW/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
cannot 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 suf-
ficient. 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.
HEAT SINK
VDD
OUT
VIA TO
SINK
C
GND
4217 F06
Figure 6. Recommended Layout
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).
VOUT
5V
Z1*
R3
200k
VDD
R2
200k
OUT
+
CL
5V
5A
100µF
EN1
GATE
EN2
R1
LTC4219DHC-5
10k
FLT
TIMER
INTVCC
C1
GND
1µF
PG
ISET
IMON
* TVS Z1: DIODES INC. SMAJ17A
Figure 7. 5V, 5A Card Resident Application
5V
R4
10k
PG = 4.35V
RMON
20k
ADC
4219 F07
For more information www.linear.com/LTC4219
4219fd
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