Linear Technology DC257 Demo Manual

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DESCRIPTIO
Demonstration circuit DC257 is a constant-frequency
step-down converter using an LTC
chronous regulator. It provides low input voltage, high
conversion efficiency for cell phones and other portable
electronics operating from one or two Li-Ion cells or three
to six NiCd cells. Constant 350kHz operation and up to
600mA output capability in an SO-8 package provide a low
noise, space-efficient solution for wireless applications.
The circuit highlights the capability of the LTC1707. De-
signed to work at low voltages, the input voltage (V
range from 2.85V to 8.5V. At V
shuts down and draws just a few microamperes, making
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PERFOR A CE SU
SYMBOL PARAMETER
V Input Voltage Range
IN
V Output Voltage
OUT
I Pulse Skipping Mode Supply Current
Q
Burst Mode Enabled Supply Current
Shutdown Current
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
LTC1707 Efficiency Curve
100
V = 3.3V
OUT
95
90
85
80
75
70
1 10
OUTPUT CURRENT (mA)
Synchronous Step-Down Regulator
®
1707 monolithic syn-
) can
IN
< 2.7V, the LTC1707
IN
W W
ARY
CONDITIONS
See Figure 2
V = 5V, SYNC/MODE = 0V, RUN/SS = 2V, I
IN
V = 5V, SYNC/MODE = 2V, RUN/SS = 2V, I
IN
V = 5V, RUN/SS = 0V, I
IN
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V = 3.6V
IN
V = 6V
IN
V = 8.4V
IN
100 1000
DC257 TA01
DEMO MANUAL DC257
NO-DESIGN SWITCHER
LTC1707 Monolithic
it ideal for single lithium-ion battery applications. DC257's
output voltage is programmable from 1.5V to 3.3V via a
jumper.
At low output currents, the LTC1707 automatically switches
TM
to Burst Mode operation to reduce switching losses and
maintain high operating efficiencies. In switching-noise
sensitive applications, Burst Mode operation can be inhib-
ited by grounding the SYNC/MODE pin or synchronizing it
with an external clock. Gerber files for this circuit board
are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
= 0mA
OUT
= 0mA
OUT
= 0mA
OUT
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Demo Board
JUMPER POSITION
2.85V to 8.5V
1.51V ±0.036V
JP1 = "1.5V"
1.82V ± 0.043V
JP1 = "1.8V"
2.52V ± 0.06V
JP1 = "2.5V"
2.94V ± 0.07V
JP1 = "2.9V"
3.33V ± 0.079V
JP1 = "3.3V"
JP1 = "OPEN"
JP1 = "3.3V"
JP1 = "3.3V"
JP1 = "3.3V"
VALUE
Note 1
300µA
200µA
15µA
1