QUICK START GUIDE FOR DEMONSTRATION CIRCUIT
1260A-A/1260A-B
2A SYNCHRONOUS STEP-UP DC/DC CONVERTER
2
Demo # Part # Part Marking Frequency
1260A-A LTC3539EDCB LDCS 1 MHz
1260A-B LTC3539EDCB-2 LDPH 2 MHz
Table 1. Demonstration Circuit Board Information
QUICK START PROCEDURE
There is one demonstration circuit board for both
LTC3539 versions. The boards are identified by the
handwritten information on the top of the pc board.
The boost converter can be evaluated using the
setup shown in Figure 1. Select one of the three out-
put voltages using the voltage select jumpers. (With
no jumper installed, the output voltage is 5V.) With
jumper JP2 in the ON position and JP1 in BURST,
connect voltmeters and ammeters as shown on the
test setup. Connect a power supply to the +V
IN
and
GND terminals and a suitable load resistor between
VOUT and GND.
With a light load (1k resistor) at the output, begin
increasing the input power supply voltage. At ap-
proximately 650mV, the output will rise to the se-
lected regulated voltage. When the output voltage
exceeds the input voltage by at least 240mV, the
converter powers itself from the output instead of
the input. This feature allows the input voltage to
drop as low as 500mV (at light loads) and still main-
tain a regulated output voltage.
Increase the input voltage to approximately 1.5V and
increase the load current. The maximum load current
depends on the input and output voltage settings.
Refer to the data sheet curves for typical output cur-
rent for various input/output voltages.
The input voltage can exceed the output voltage and
still maintain regulation, although the load current is
less and efficiency is lower. It should be noted that
the output voltage ripple will increase as Vin ap-
proaches Vout. The increase will occur in a narrow
range when Vin is between 100 and 300mV below
Vout. The ripple voltage in this range can be from
30mV to 100mV pp.
When evaluating the circuit at very low input volt-
ages, it is important to monitor the input voltage di-
rectly at the input terminals of the circuit board. At
these low input voltages, any voltage drop in the
power supply wire, connections and Ammeter will
result in the input voltage at the input terminals
dropping below the minimum voltage required for
operation.
Additional pc board pads are provided for an optional
input bypass capacitor (C1). It maybe necessary
when using long wires between the power supply
and circuit board, or for adding a tantalum capacitor
to minimize input voltage transients that may occur
when the input is hot-switched. Additional pads di-
rectly above the output capacitor (C4) are provided if
additional output capacitance is needed.
When verifying output ripple, it is important to use
the scope probe connection as shown in figure 3.
Typical output voltage ripple with a 1k and 100-Ohm
load are shown in figure 2. The 1k load shows Burst
mode ripple, while the 100 Ohm load is fixed fre-
quency PWM mode.
See LTC3539/3539-2 Data Sheet for additional information
