REG5601 datasheet(3/3 Pages) BURR-BROWN

3 / 3 page

REG5601

4.7µF Tantalum

2.9V

T18

Termpwr

REG5601

Regulator

Output

Disconnect

T18

Termpwr

REG5601

Regulator

Output

Disconnect

SCSI

Cable

4.7µF Tantalum

4V to 5.25V

4.7µF Tantalum

4V to 5.25V

4.7µF

Tantalum

2.9V

0 = Termination On

1 = Disconnect

0 = Termination On

1 = Disconnect

Gnd

(18 Lines)

Controller

Transceivers

Controller

Transceivers

FIGURE 1. Standard SCSI Termination Application.

CIRCUIT BOARD

JUNCTION TO LEAD

BOARD TO AMBIENT

JUNCTION TO AMBIENT

PACKAGE

MATERIAL

(

°C/W)

(

°C/W)

(

°C/W)

SO-28

1-Layer(1)

3-Layer(2)

Aluminum(3)

SSOP-28

1-Layer(1)

3-Layer(2)

Aluminum(3)

NOTES: (1) Single-side layout on 0.062 inch FR4, 1 oz copper. (2) Three-layer layout on 0.062 inch FR4, 1 oz copper.

(3) Aluminum 0.062 inch substrate, 0.003 insulation, one layer, 1 oz copper (Thermal Clad, Bergqueist Co.)

FIGURE 2. Circuit Board Layout.

The REG5601 has current limit and thermal shutdown that

protect it from damage during output short-circuit or overload.

The current limit is approximately 1350mA and thermal

shutdown activates at a junction temperature of approxi-

mately 175

°C. For good reliability, the junction temperature

should not exceed 125

°C. Any tendency to activate the

thermal shutdown during normal operation is an indication of

inadequate heat sinking and/or excessive power dissipation.

Heat is dissipated primarily by conduction through the leads

to circuit board traces. It is important to connect the six

thermal ground leads (7, 8, 9, 20, 21, 22) to a large circuit

trace—see Figure 2. Measured values of thermal resistance

for various circuit board materials are shown. These are

approximate values. Variations in circuit board pattern,

mounting techniques, air flow, proximity to other circuit

boards and heat sources will affect thermal performance.

A simple experiment will determine whether the actual circuit

board layout is adequate (i.e.,

BA is low enough) so that the

maximum recommended junction temperature of the REG5601

will not be exceeded. The procedure uses the internal thermal

shutdown feature of the REG5601 (at TJ ≈ 175°C) to deter-

mine when the junction is approximately 50

°C above the

maximum recommended junction temperature (TJ = 125°C).

Operate the circuit with normal or other desired test electrical

conditions. Increase the ambient temperature and determine

the value at which thermal limit occurs (by sensing a sudden

drop in VREG output). At this point TJ is approximately 175°C.

If this occurs at an ambient temperature of more than 50

°C

above the system ambient temperature design goal, the TJ will

not exceed 125

°C under the same electrical conditions when

the ambient temperature is at the system design goal value.

TJ = TA + PD θJA

Thermal ground (leads 7, 8, 9, 20, 21, 22).

Connect to circuit ground or leave open-circuit.

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