LT1940L Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LT1940L

Dual Monolithic 1.4A, 1.1MHz Step-Down Switching Regulator

Linear Technology 

APPLICATIO S I FOR ATIO

VIN SW

GND

LT1940/LT1940L

VIN SW

GND

(7a)

IC1

VSW

VIN SW

C1

GND

L1

D1

(7b)

C2

(7c)

1940 F07

Figure 7. Subtracting the Current when the Switch is ON (a) From the Current when the Switch is OFF (b) Reveals the Path

of the High Frequency Switching Current (c) Keep This Loop Small. The Voltage on the SW and BOOST Nodes will also be

Switched; Keep these Nodes as Small as Possible. Finally, Make Sure the Circuit is Shielded with a Local Ground Plane.

VOUT1

GND

VIA TO LOCAL GROUND PLANE

VIA TO VIN

VOUT2

1940 F08

Figure 8. A Good PCB Layout Ensures Proper Low EMI Operation

Thermal Considerations

The PCB must also provide heat sinking to keep the

LT1940 cool. The exposed metal on the bottom of the

package must be soldered to a ground plane. This ground

should be tied to other copper layers below with thermal

vias; these layers will spread the heat dissipated by the

LT1940. Place additional vias near the catch diodes.

Adding more copper to the top and bottom layers and tying

this copper to the internal planes with vias can reduce

thermal resistance further. With these steps, the thermal

resistance from die (or junction) to ambient can be re-

duced to θJA = 45°C/W.

The power dissipation in the other power components—

catch diodes, boost diodes and inductors,␣ cause addi-

tional copper heating and can further increase what the IC

sees as ambient temperature. See the LT1767 data sheet’s

Thermal Considerations section.

Single, Low-Ripple 2.8A Output

The LT1940 can generate a single, low-ripple 2.8A output

if the outputs of the two switching regulators are tied

together and share a single output capacitor. By tying the

two FB pins together and the two VC pins together, the two

channels will share the load current. There are several

advantages to this two-phase buck regulator. Ripple cur-

rents at the input and output are reduced, reducing voltage

ripple and allowing the use of smaller, less expensive

1940fa

15

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