LT3063 datasheet(21/30 Pages) LINEAR

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LT6658

6658f

For more information www.linear.com/LT6658

SUPPLY VOLTAGE (V)

6658 F20

200mA

NO LOAD

Figure 20. Power Dissipation vs Supply Voltage

Safe Operating Area

The safe operating area, or SOA, describes the operating

region where the junction temperature does not exceed

TJMAX. In Figure 21, the SOA for the LT6658 is plotted. In

this plot, the output voltage is 2.5V and the output current

is the combined current of both channels. The SOA is plot-

ted for three values of

θJA. This illustrates how a lower θJA

value will remove more heat and allow more power to be

dissipatedthroughthepackagewithoutdamagingthepart.

SUPPLY VOLTAGE – LOAD VOLTAGE (V)

6658 F21

1000

100

θJA = 35°C/W

θJA = 60°C/W

θJA = 85°C/W

TA = 25°C

Figure 21. SOA for the LT6658

applicaTions inForMaTion

There are three regions in the SOA plot. The top left region

is the maximum rated current of the LT6658. The diagonal

lines in the middle are where both the load current and

supply voltage must be reduced as not to exceed TJMAX.

The bottom right is the maximum voltage of the LT6658.

It is important to realize the SOA limit is an absolute maxi-

mum rating at TJMAX. It is not recommended to operate

at this limit for extended periods of time.

PCB Layout

The LT6658 is a high performance reference and there-

fore, requires good layout practices. Each supply pin

should have 0.1µF capacitor placed close to the package.

The output capacitors should also be close to the part to

keep the equivalent series resistance to a minimum. As

mentioned earlier, avoid parasitic resistance between the

sense line and the load. Any error here will directly affect

the output voltage.

All three ground pins (1, 2, 6) , and exposed pad should

be connected together, preferably in a star ground con-

figuration or ground plane. The exposed pad, Pin 17, is

electrically connected to the die and must be connected to

ground. It is also necessary for good thermal conductivity

to use plenty of copper and multiple vias.

If the design requires the part to dissipate significant

power, consider using 2oz copper and/or a multilayer

boardwithalargeareaofcopperconnectedtotheexposed

pad. Note that

θJA is proportional to the amount of copper

soldered to the exposed pad. Preferably the copper should

be on the outermost layers of the board for good thermal

dissipation. A sample layout is shown in Figure 22a. The

sense lines, VOUT1_S and VOUT2_S should connect as close

as possible to the top of the load. In Figure 22b, a star

ground is shown where the LT6658 ground is directly

connected to the bottom of the load. Connect all other

grounds in the system to this same point. Minimize the

resistance between GND side of the load and the LT6658

GND pins, especially for applications where the LT6658

is sinking current. This minimizes load regulation errors.

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