LT3503 データシートの表示（PDF） - Linear Technology

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LT3503

1A, 2.2MHz Step-Down Switching Regulator in 2mm × 3mm DFN

Linear Technology 

APPLICATIO S I FOR ATIO

VIN

SHUTDOWN

C2 D1

C1

LT3503

SYSTEM

GROUND

VOUT

: VIAS TO LOCAL GROUND PLANE

: OUTLINE OF LOCAL GROUND PLANE

3503 F12

Figure 12. A Good PCB Layout Ensures Proper, Low EMI Operation

local, unbroken ground plane below these components,

and tie this ground plane to system ground at one location,

ideally at the ground terminal of the output capacitor C1.

The SW and BOOST nodes should be as small as possible.

Finally, keep the FB node small so that the ground pin and

ground traces will shield it from the SW and BOOST nodes.

Include vias near the exposed GND pad of the LT3503 to

help remove heat from the LT3503 to the ground plane.

High Temperature Considerations

The die temperature of the LT3503 must be lower than the

maximum junction of 125°C. This is generally not a

concern unless the ambient temperature is above 85°C.

For higher temperatures, care should be taken in the layout

of the circuit to ensure good heat sinking of the LT3503.

The maximum load current should be derated as the

ambient temperature approaches 125°C. The die tem-

perature is calculated by multiplying the LT3503 power

dissipation by the thermal resistance from junction to

ambient. Power dissipation within the LT3503 can be

estimated by calculating the total power loss from an

efficiency measurement and subtracting the catch diode

loss. The resulting temperature rise at full load is nearly

independent of input voltage. Thermal resistance depends

on the layout of the circuit board, but 64°C/W is typical for

the (2mm × 3mm) DFN (DCB) package.

Outputs Greater Than 6V

For outputs greater than 6V, add a resistor of 1k to 2.5k

across the inductor to damp the discontinuous ringing of

the SW node, preventing unintended SW current.

Other Linear Technology Publications

Application notes AN19, AN35 and AN44 contain more

detailed descriptions and design information for Buck

regulators and other switching regulators. The LT1376

data sheet has a more extensive discussion of output

ripple, loop compensation and stability testing. Design

Note DN100 shows how to generate a bipolar output

supply using a Buck regulator.

3503f

17

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