10

LTC1682/LTC1682-3.3/LTC1682-5

General Layout Considerations

Due to the high switching frequency and high transient

currents produced by the device, careful board layout is a

must. A clean board layout using a ground plane and short

connections to all capacitors will improve noise perfor-

mance and ensure proper regulation (Figure 5).

The FILT pin on the LTC1682-3.3/LTC1682-5 is a high

impedance node. Leakage currents at this pin must be

minimized.

Measuring Output Noise

Measuring the LTC1682 low noise levels requires care.

Figure 6 shows a test setup for taking the measurement.

Good connection and signal handling technique should

yield about 500

measurement involves AC coupling the LTC1682 output

into the test setup’s input and terminating this connection

with 50

Ω. Coaxial connections must be maintained to

preserve measurement integrity.

Power-On Reset

Upon initial power-up, a power-on reset circuit ensures

that the internal functions are correctly initialized when

power-on reset circuit will enable the part as long as the

SHDN pin is held high.

Thermal Considerations

The power handling capability of the device will be limited

by the maximum rated junction temperature (125

°C). The

through its pins, especially GND (Pin 4). Thermal resis-

tance to ambient can be optimized by connecting GND to

a large copper region on the PCB, which serves as a heat

sink. Applications which operate the LTC1682 near maxi-

mum power levels should maximize the copper area at all

some airflow over the part to carry away excess heat.

1

2

3

4

LTC1682-3.3/5

8

7

6

5

C1

1682 F05

C3

C2

GND

SHDN

C4

LTC1682

DEMO

BOARD

OSCILLOSCOPE

BANDWIDTH

FILTER

CONNECT BNC AND

OUTPUT CAPACITOR

GROUND TERMINAL E5

PLACE COUPLING

CAPACITOR IN SHIELDED

BOX WITH COAXIAL

CONNECTOR

COUPLING

CAPACITOR

BNC CABLES

OR COUPLERS

BATTERY OR

LOW NOISE DC

POWER SUPPLY

R*

R*

*50

Ω TERMINATIONS

HP-11048C OR

EQUIVALENT

R*

NOTE: KEEP BNC CONNECTIONS

AS SHORT AS POSSIBLE

PLACE BANDWIDTH FILTER

COMPONENTS IN SHIELDED BOX

WITH COAXIAL CONNECTORS

PREAMPLIFIER

1822

INPUT

1682 F06

20dB

Figure 6. LTC1682 Noise Measurement Test Setup

Figure 5