LT3430_15 Datasheet, PDF (26/28 Pages) Linear Technology – High Voltage, 3A, 200kHz/100kHz Step-Down Switching Regulators

LT3430/LT3430-1
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 significantly
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
=
DC
f
• V_IN
•L
DC = Duty Cycle = ^{VOUT + VF}
V_OUT + V_IN + V_F
I_COUT
(RMS) =
I_P-P
12
The output ripple voltage for this configuration 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_OUT
(V_IN
+ V_OUT
V_IN
)
+
(V_IN)(V_OUT )
2(L)(f)(V_IN + V_OUT
)
Discontinuous Mode = ^{2(IOUT )(VOUT )}
(L)(f)
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.
TYPICAL APPLICATION
V_IN
5.5V*
TO 60V
3.3V, 2A Buck Converter
MMSD914TI
6
BOOST
3, 4
2, 5
V_IN
SW
4.7µF
100V
LT3430-1
15
OFF ON
SHDN
10
BIAS
14
SYNC
GND
1, 8, 9, 16
12
FB
V_C
11
220pF
3.3k
1.5µF
68µH
30BQ060
+
20.5k
12.1k
V_OUT
3.3V
2A
100µF 10V
SOLID
TANTALUM
2 IN PARALLEL
0.022µF
3430 F16
*FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
34301fa
26