Datasheet

LT8582
13
8582f
Boost Converter Component Selection
Table 1. Boost Converter Design Equations
PARAMETERS/EQUATIONS
Step 1: Inputs Choose V
IN
, V
OUT
and f
OSC
to calculate equations
below.
Step 2: DC
DC ≅
V
OUT
–V
IN
+ 0.5V
V
OUT
+ 0.5V– 0.3V
Step 3: L1
L
TYP
=
(V
IN
– 0.3) •DC
f
OSC
•1A
(1)
L
MIN
=
(V
IN
–0.3V)•(2•DC–1)
1.7A • f
OSC
•(1–DC)
(2)
L
MAX
=
(V
IN
–0.3V)•DC
f
OSC
•0.18A
(3)
• Solve equations 1, 2 and 3 for a range of L
values
• The minimum of the L value range is the
higher of L
TYP
and L
MIN
• The maximum of the L value range is L
MAX
Step 4: I
RIPPLE
I
RIPPLE
=
(V
IN
– 0.3V) •DC
f
OSC
•L
1
Step 5: I
OUT
I
OUT
=
3A–
I
RIPPLE
2
⎛
⎝
⎜
⎞
⎠
⎟
•
(1– DC)
Step 6: D1 V
R
≥ V
OUT
; I
AVG
≥ I
OUT
Step 7: C
OUT
C
OUT1
" C
OUT2
v
I
OUT
tDC
f
OSC
(0.01t V
OUT
–0.5t I
OUT
tR
DSON_PMOS
)
• If PMOS is not used, then use just one
capacitor where C
OUT
= C
OUT1
+ C
OUT2
Step 8: C
IN
C
IN
v C
VIN
 C
PWR
v
3AtDC
50
t
f
OSC
t
0.005
t
V
IN
8
t
f
OSC
t
0.005
t
V
IN

I
RIPPLE
Step 9: R
FBX
R
FBX
=
V
OUT
– 1.204V
83.3µA
⎛
⎝
⎜
⎞
⎠
⎟
Step 10: R
T
R
T
=
81.6
f
OSC
–1; f
OSC
in MHz andR
T
in kΩ
Step 11: PMOS Only needed for input or output disconnect. See
PMOS Selection in the Appendix for information
on sizing the PMOS and the biasing resistor,
R
GATE
and picking appropriate UVLO components.
Note 1: Above equations use numbers good for many applications but
for more exact results use the equations from the appendix with numbers
from the Electrical Characteristics.
Note 2: The final values for C
OUT1
, C
OUT2
and C
IN
may deviate from the
above equations in order to obtain desired load transient performance.
APPLICATIONS INFORMATION
Figure 5. Boost Converter – The Component Values Given
Are Typical Values for a 1.5MHz, 5V to 12V Boost
Each channel of the LT8582 can be configured as a boost
converter as in Figure 5. This topology allows for positive
output voltages that are higher than the input voltage. An
external PMOS (optional) driven by the GATE pin of the
LT8582 can achieve input or output disconnect during a
FAULT event, SHDN < 1.31V, or V
IN
< 2.3V. Figure 5 shows
the configuration for output disconnect. A single feedback
resistor sets the output voltage. For output voltages higher
than 40V, see the Charge Pump Topology in the Charge
Pump Aided Regulators section.
Table 1 is a step-by-step set of equations to calculate
component values for the LT8582 when operating as a
boost converter. Input parameters are input and output
voltage and switching frequency (V
IN
, V
OUT
and f
OSC
re-
spectively). Refer to the Appendix for further information
on the design equations presented in Table 1.
Variable Definitions:
V
IN
= Input Voltage
V
OUT
= Output Voltage
DC = Power Switch Duty Cycle
f
OSC
= Switching Frequency
I
OUT
= Maximum Output Current
I
RIPPLE
= Inductor Ripple Current
R
DSON_PMOS
= R
DSON
of External Output PMOS (set to 0
if not using PMOS)
SS
GNDSYNC
SWB
D1
30V, 2A
M1
SWA
LT8582
CHx
8582 F05
PG
RT
215k
V
IN
SHDN
CLKOUT
V
C
FBX
GATE
V
OUT
12V
0.8A
V
IN
5V
100k
R
T
53.6k
C
OUT1
10µF
6.04k
6.49k
L1
4.7µH
OPTIONAL
R
FBX
130k
C
IN
4.7µF
0.1µF 4.7nF
47pF
C
OUT2
10µF