REV.

ADP3334

–9–

3. The solder mask opening should be about 120 microns

(4.7 mils) larger than the pad size resulting in a minimum

60 micron (2.4 mils) clearance between the pad and the

solder mask.

4. The paste mask opening is typically designed to match the

pad size used on the peripheral pads of the LFCSP package.

This should provide a reliable solder joint as long as the

stencil thickness is about 0.125 mm.

The paste mask for the thermal pad needs to be designed for

the maximum coverage to effectively remove the heat from the

package. However, due to the presence of thermal vias and the

size of the thermal pad, eliminating voids may not be possible.

5. The recommended paste mask stencil thickness is 0.125 mm.

A laser cut stainless steel stencil with trapezoidal walls should

be used.

A “No Clean” Type 3 solder paste should be used for mount-

ing the LFCSP package. Also, a nitrogen purge during the

reflow process is recommended.

6. The package manufacturer recommends that the reflow

temperature should not exceed 220°C and the time above

liquidus is less than 75 seconds. The preheat ramp should be

3°C/second or lower. The actual temperature profile depends

on the board density and must determined by the assembly

house as to what works best.

Use the following general guidelines when designing printed

circuit boards.

1. Keep the output capacitor as close as possible to the out-

put and ground pins.

2. Keep the input capacitor as close as possible to the input

and ground pins.

3. PC board traces with larger cross sectional areas will remove

more heat from the ADP3334. For optimum heat transfer,

specify thick copper and use wide traces.

4. Use additional copper layers or planes to reduce the

thermal resistance. When connecting to other layers, use

multiple vias if possible.

Shutdown Mode

Applying a TTL high signal to the shutdown (SD) pin or the

input pin will turn the output off. Pulling SD down to 0.4 V or

below or tying it to ground will turn the output on. In shutdown

mode, quiescent current is reduced to much less than 1 µA.

C