4
DEMO MANUAL DC195
NO-DESIGN SWITCHER
QUICK START GUIDE
This demonstration board is easily set up to evaluate the
performance of the LTC1627 IC. Please follow the proce-
dure outlined below for proper operation.
• Refer to Figure 6 for proper connection of monitoring
equipment to ensure correct measurement.
• Connect the input power supply to the V
IN
and GND
terminals on the left-hand side of the board. Do not
increase V
IN
over 10V or the Zener, D2, will be
damaged. Select the appropriate position of jumper
JP1 for the V
IN
voltage (position “V
IN
<5V” for V
IN
<4.5V only).
• Connect the load between the V
OUT
and GND
terminals on the right side of the board.
• The RUN/SS pin can be left unconnected. To shut
down the LTC1627, tie this pin to GND.
• Set the desired output voltage with jumper JP2, as
shown in Figure 2 and Table 1.
Table 1. Maximum Allowable Input Voltage vs Selected
Output Voltage and JP1 Position
MAXIMUM V
IN
FOR JP1 POSITION
“≥ 5V” “< 5V” (Note 1)
1.8V 8.5V 4.5V
2.5V 8.5V 4.5V
2.9V 8.5V 4.5V
3.3V 8.5V 4.5V
N/A
JP2 OUTPUT VOLTAGE
Note 1: The silkscreen label “<5V” on the demo board is a simplified
notation. The actual voltage should be ≤4.25V.
OPERATIO
U
The circuit in Figure 1 highlights the capabilities of the
LTC1627. The application circuit is set up for a variety of
output voltages. Output voltages from 1.8V to 3.3V or user
programmable voltages can be obtained by selecting the
appropriate jumper position.
The LTC1627 is a monolithic synchronous step-down
switching regulator using a fixed-frequency architecture.
Burst Mode operation provides high efficiency at low load
currents. Operating efficiencies typically exceed 90% over
two decades of load current range. 100% duty cycle
provides low dropout operation, which extends operating
time in battery-operated systems.
Do not use small spring-clip leads when testing this
circuit. Small spring-clip leads are very convenient for
small-signal bench testing and voltage measurements,
but should not be used with this circuit. Soldered wire
connections are required to properly ascertain the perfor-
mance of the PC board.
This demonstration board is intended for the evaluation of
the LTC1627 switching regulator IC and was not designed
for any other purpose.
The operating frequency of this demo circuit is 350kHz,
the frequency of the LTC1627’s internal oscillator. For
higher frequencies, SYNC/FCB (E1) can be synchronized
with an external clock. Burst Mode operation is automati-
cally disabled when the SYNC/FCB pin is externally driven.
Grounding SYNC/FCB also disables Burst Mode opera-
tion, potentially reducing noise and interference.
Soft start is provided by an external capacitor, C
SS
, which
can be used to properly sequence supplies. The maximum
operating current level is 0.5A.
This demo board is optimized for 3.3V outputs and 5V
input. Output voltages from 1.8V to 3.3V are available by
selecting the appropriate jumper position of JP2. For other
output voltages, select the OPEN (E) position and add an
1.8V 2.5V 2.9V 3.3V OPEN
JP2
DC195 • F02
Figure 2. Output Voltage Selection (JP2)
(3.3V Position Shown)
