Datasheet

LT3430/LT3430-1
26
34301fa
APPLICATIONS INFORMATION
value equal to the peak-to-peak triangular waveform of the
inductor. The low output ripple design in Figure 15 places
the input capacitor between V
IN
and the regulated negative
output. This placement of the input capacitor signifi cantly
reduces the size required for the output capacitor (versus
placing the input capacitor between V
IN
and ground).
The peak-to-peak ripple current in both the inductor and
output capacitor (assuming continuous mode) is:
I
P-P
P-P
=
==
+
++
=
DC V
fL
DC Duty Cycle
VV
VVV
I RMS
I
IN
OUT F
OUT IN F
COUT
•
•
()
12
The output ripple voltage for this confi guration is as low
as the typical buck regulator based predominantly on the
inductor’s triangular peak-to-peak ripple current and the
ESR of the chosen capacitor (see Output Ripple Voltage
in Applications Information).
Diode Current
Average diode current is equal to load current. Peak diode
current will be considerably higher.
Peak diode current:
Continuous Mode
I
VV
V
VV
LfV V
Discontinuous Mode
IV
Lf
OUT
IN OUT
IN
IN OUT
IN OUT
OUT OUT
=
+
+
+
=
()()()
()()( )
()( )
()()
2
2
Keep in mind that during start-up and output overloads,
average diode current may be much higher than with nor-
mal loads. Care should be used if diodes rated less than
1A are used, especially if continuous overload conditions
must be tolerated.
BOOST
V
IN
6
2, 5
10
12
30BQ060
20.5k
V
OUT
3.3V
2A
3, 4
15
14
11
220pF
0.022µF
*FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
1, 8, 9, 16
LT3430-1
SHDN
SYNC
SW
BIAS
FB
V
C
GND
1.5µF
100µF 10V
SOLID
TANTALUM
2 IN PARALLEL
68µH
MMSD914TI
12.1k
3430 F16
4.7µF
100V
ONOFF
V
IN
5.5V*
TO 60V
+
3.3k
3.3V, 2A Buck Converter
TYPICAL APPLICATION