DC289 Introduction
Description
Demonstration Circuit DC289 is a step-down (buck) regulator using the LTC®1701. The
combination of the LTC1701’s tiny SOT-23 package and high switching frequency
results in a highly efficient application in a small board space. It is ideal for cell phones
and other portable electronics operating from one Li-Ion cell or three to four NiCd or
NiMH cells. DC289 operates from a 2.5 to 5.5V input voltage range and is capable of
providing 0.5A with a jumper-selectable output voltage of 1.5/2.5/3.3V-ADJ.
This board highlights the capabilities of the LTC1701, which uses a current mode,
constant off-time architecture to control an internal P-channel power MOSFET at about
1MHz. This high performance power supply occupies less than 0.3 square inches and has
low output voltage ripple and fast transient response.
At low output currents, the LTC1701 automatically switches to Burst Mode™ operation
to maintain high operating efficiencies by minimizing supply current. The part can be
shut down by pulling the ITH/RUN pin low, further reducing the supply current to less
than 1µA.
In dropout, the P-channel MOSFET is turned on continuously (100% duty cycle),
providing low dropout operation with VOUT ≅ VIN, thereby maximizing battery life.
Quick Start Guide
Demonstration Board DC289 is easy to set up for evaluation of the LTC1701. Please
follow the procedure below for proper operation:
1.
2.
3.
4.
Move jumper JP1 to the appropriate position for the required output voltage. For
voltages other than the preset value, make sure you install the calculated resistor at
the pad provided for R7.
To shut down the circuit, connect the ITH/RUN terminal to ground. When the part is
not shut down, be careful not to add excessive capacitance to the ITH/RUN pin, since
it affects the transient response.
Connect the input power supply to the VIN and GND terminals.
Connect the load between the VOUT and GND terminals. Refer to the connection
diagram (Figure 1) for proper measurement equipment setup. XXXYYYY
'SCOPE
+
–
+
–
+–
+
–
LOAD
+
+
–
GND
V
OUT
GND
I
TH
/
RUN
V
IN
DC289A
0.5A, SOT-23, DC/DC CONVERTER
LTC1701
1.5
2.5
ADJ
JP1
Figure 1. DC289A Connection Diagram
