QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 476
1.25MHZ 3A PEAK SWITCH CURRENT MONOLITHIC STEP-DOWN CONVERTER
part in determining the minimum input voltage for a se-
lected output over the full current range of the applica-
tion. For this demonstration board, with up to 2A output
current, the minimum input voltages required to main-
tain regulated output voltages is listed below. Custom-
izable output voltages of 2.5V and 1.8V are very com-
mon and are thus additionally listed in the table (see
Customizing the Board below). If the input voltage falls
below the minimum input voltage listed below, the out-
put voltage can drop accordingly from the programmed
output voltage. This mode is called maximum duty cycle
drop-out.
Table 3.
Minimum Input Voltage vs Output Voltage
MINIMUM INPUT VOLTAGE VIN (V) OUTPUT VOLTAGE (V)
7 5
4.7 3.3
3.7 2.5
3 1.8
CUSTOMIZING THE BOARD
The components used in this demonstration circuit are
optimized for a wide input voltage range. Nevertheless,
the bandwidth can be increased for more specific input
voltages such as 12V±10% or 5V±10% if desired. Some
typical applications are shown in Figure 5 to Figure 11.
The adjustable feedback resistors allow the output volt-
age to be customized. For output voltages below 3.3V,
the boost diode should be moved from D2 to D3 to pro-
vide the minimum boost voltage required for the internal
power switch. Make sure that the boost capacitor (C8)
has a voltage rating greater than or equal to the output
voltage for applications where the boost diode is placed
in D2. However, the boost capacitor must have a voltage
rating greater than the input voltage whenever the boost
diode is placed in position D3.
+
–
LOAD
+
–
+
–
+
–
+
–
+
–
+
–
Figure 4.
Proper Measurement Equipment Setup
3
