EL7535 データシートの表示（PDF） - Intersil

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EL7535

Monolithic 350mA Step-Down Regulator

Intersil 

EL7535

point. The equation below shows the pole frequency

relationship:

fP

=

-------------------1--------------------

2π(R1 R2)C4

Current Limit and Short-Circuit Protection

The current limit is set at about 1.5A for the PMOS. When a

short-circuit occurs in the load, the preset current limit

restricts the amount of current available to the output, which

causes the output voltage to drop below the preset voltage.

In the meantime, the excessive current heats up the

regulator until it reaches the thermal shut-down point.

Thermal Shut-Down

Once the junction reaches about 145°C, the regulator shuts

down. Both the P channel and the N channel MOSFETs turn

off. The output voltage will drop to zero. With the output

MOSFETs turned off, the regulator will soon cool down.

Once the junction temperature drops to about 130°C, the

regulator will restart again in the same manner as EN pin

connects to logic HI.

Thermal Performance

The EL7535 is in a fused-lead MSOP10 package. Compared

with regular MSOP10 package, the fused-lead package

provides lower thermal resistance. The θJA is 100°C/W on a

4-layer board and 125°C/W on 2-layer board. Maximizing the

copper area around the pins will further improve the thermal

performance.

Layout Considerations

The layout is very important for the converter to function

properly. The following PC layout guidelines should be

followed:

• Separate the Power Ground ( ) and Signal Ground ( );

connect them only at one point right at the pins

• Place the input capacitor as close to VIN and PGND pins

as possible

• Make the following PC traces as small as possible:

- from LX pin to L

- from CO to PGND

• If used, connect the trace from the FB pin to R1 and R2 as

close as possible

• Maximize the copper area around the PGND pin

• Place several via holes under the chip to additional ground

plane to improve heat dissipation

The demo board is a good example of layout based on this

outline. Please refer to the EL7535 Application Brief.

8

FN7003.5

July 13, 2006

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