1
DEMO MANUAL DC257
NO-DESIGN SWITCHER
LTC1707 Monolithic
Synchronous Step-Down Regulator
Demonstration circuit DC257 is a constant-frequency
step-down converter using an LTC
®
1707 monolithic syn-
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
IN
) can
range from 2.85V to 8.5V. At V
IN
< 2.7V, the LTC1707
shuts down and draws just a few microamperes, making
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
to Burst Mode
TM
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.
SYMBOL
PARAMETER
CONDITIONS
JUMPER POSITION
VALUE
V
IN
Input Voltage Range
2.85V to 8.5V
V
OUT
Output Voltage
See Figure 2
JP1 = “1.5V”
1.51V
±
0.036V
JP1 = “1.8V”
1.82V
±
0.043V
JP1 = “2.5V”
2.52V
±
0.06V
JP1 = “2.9V”
2.94V
±
0.07V
JP1 = “3.3V”
3.33V
±
0.079V
JP1 = “OPEN”
Note 1
I
Q
Pulse Skipping Mode Supply Current
V
IN
= 5V, SYNC/MODE = 0V, RUN/SS = 2V, I
OUT
= 0mA
JP1 = “3.3V”
300
µ
A
Burst Mode Enabled Supply Current
V
IN
= 5V, SYNC/MODE = 2V, RUN/SS = 2V, I
OUT
= 0mA
JP1 = “3.3V”
200
µ
A
Shutdown Current
V
IN
= 5V, RUN/SS = 0V, I
OUT
= 0mA
JP1 = “3.3V”
15
µ
A
LTC1707 Efficiency Curve
OUTPUT CURRENT (mA)
1
70
EFFICIENCY (%)
90
95
100
10
100
1000
DC257 TA01
85
80
75
V
OUT
= 3.3V
V
IN
= 6V
V
IN
= 3.6V
V
IN
= 8.4V
Demo Board
Burst Mode is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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