LTC4282 datasheet(29/32 Pages) AD

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LTC4238

Rev. 0

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Second, check the temperature rise in channel 1 after

startup when TMR times out under different overload

conditions. In this example, IPT015N10N5 can take 60A

with 40V across it for 100µs. The temperature rise in 20µs

is insignificant under overload conditions. If the worst-

case temperature rise in channel 1 is too high, better SOA

MOSFET(s) must be selected for it.

Layout Considerations

For high current applications, PCB layout plays a critical

role in minimizing current congestion as well as partition-

ing the current between two channels. In parallel mode,

to achieve the even split of current flow between the two

channels, the two high current paths should have very

similar layouts for the RSENSE and MOSFET placements.

To achieve accurate current sensing, Kelvin connec-

tions are also required. The SENSE+ and SENSE– lines

should be laid out as differential signal pair. Their trace

lengths to LTC4238 pins should be as short as possible.

The minimum trace width for 1oz copper foil is 0.02" per

amp to make sure the trace stays at a reasonable tem-

perature. Using 0.03" per amp or wider is recommended.

Note that 1oz copper exhibits a sheet resistance of about

530μΩ/. Small resistances add up quickly in high cur-

rent applications.

To improve noise immunity, place the resistive voltage

dividers for the UV, OV and FB pins close to the device and

keep traces to VDD and GND short. It is also important

to put the INTVCC bypass capacitor as close as possible

between the INTVCC and GND pins. A 0.1μF capacitor,

CF, from the UV pin (and OV pin through resistor R2)

to GND also helps reject supply noise. Figure 11 shows

a layout that addresses these issues. Note that a surge

suppressor, Z1, is placed between supply and ground

using wide traces.

It is advised to avoid placing the ground plane under the

power MOSFETs. If the MOSFETs overheat, the insulation

could fail between the input voltage at their drains and an

underlying ground plane. This could create a catastrophic

short across the supply.

APPLICATIONS INFORMATION

Figure 11. Recommended PCB Layout

4238 F11

SENSE RESISTOR RS

ILOAD

GND

VIN

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