DEMO MANUAL DC326B
NO-DESIGN SWITCHER
OPERATION
How to Measure Voltage Regulation and Efficiency
When measuring voltage regulation or efficiency, voltage measurements should be made directly across the VOUT and GND terminals, not at
the end of test leads at the load. Similarly, input voltage should be measured directly at the VIN and GND terminals of the LT1766 demo board.
Input and output current should be measured by placing an ammeter in series with the input supply and load. Refer to figure 2 for proper
monitoring equipment setup.
How to Measure Output Voltage Ripple
When measuring output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. A sturdy wire should be
soldered to the output side of the GND terminal. The other end of the wire is looped around the ground side of the probe and should be kept
as short as possible. The tip of the probe is touched directly to VOUT (see Figure 3). Bandwidth is generally limited to 20MHz for ripple
measurements. Also, if multiple pieces of line-powered test equipment are used, be sure to use isolation transformers on their power lines
to prevent ground loops, which can cause erroneous results. Figure 4 shows the output voltage ripple with a steady-state load of 1A for the
LT1766.
Heat Dissipation Issues
Since the LT1766 includes a 1.5A onboard power switch, care must be taken not to exceed the 125c maximum operating junction temperature
for the part. A simple technique is to use the PC board as a heat sink. On the LT1766 demo board, the power IC is surrounded by ground plane
on both sides of the PC board. The two sides are connected through vias to better handle the power dissipation. If the LT1766 is laid out on a
multilayer board, there should be metal on the inner layers directly underneath the LT1766. This helps in spreading heat and improves the
power dissipation capability of the PCB.
Note: See 'Thermal Calculations' section in the Applications Information of the LT1766 datasheet.
