LT1936
16
1936fd
APPLICATIONS INFORMATION
One method of damping the tank circuit is to add another
capacitor with a series resistor to the circuit. In Figure 8b
an aluminum electrolytic capacitor has been added. This
capacitor’s high equivalent series resistance damps the
circuit and eliminates the voltage overshoot. The extra
capacitor improves low frequency ripple fi ltering and
can slightly improve the effi ciency of the circuit, though
it is likely to be the largest component in the circuit. An
alternative solution is shown in Figure 8c. A 0.7Ω resistor
is added in series with the input to eliminate the voltage
overshoot (it also reduces the peak input current). A 0.1μF
capacitor improves high frequency fi ltering. This solution
is smaller and less expensive than the electrolytic capacitor.
For high input voltages its impact on effi ciency is minor,
reducing effi ciency by one percent for a 5V output at full
load operating from 24V.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
Outputs Greater Than 6V
For outputs greater than 6V, add a resistor of 1k to 2.5k
across the inductor to damp the discontinuous ringing
of the SW node, preventing unintended SW current. The
12V Step-Down Converter circuit in the Typical Applica-
tions section shows the location of this resistor. Also note
that for outputs above 6V, the input voltage range will be
limited by the maximum rating of the BOOST pin. The 12V
circuit shows how to overcome this limitation using an
additional Zener diode.
3.3V Step-Down Converter
TYPICAL APPLICATIONS
V
IN
4.5V TO 36V
ON OFF
D1
D2
L1
10μH
R1
17.4k
C2
47μF
1936 TA03
C1
4.7μF
C3
0.22μF
V
OUT
3.3V
1.2A
V
IN
BOOST
V
C
GND
COMP FB
LT1936
SHDN SW
R2
10k
