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LT3581EMSE#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36
LT3581
13
3581fb
For more information www.linear.com/LT3581
APPLICATIONS INFORMATION
Figure 5. Boost Converter – The Component Values and Voltages
Given Are Typical Values for a 2MHz, 5V to 12V Boost
BOOST CONVERTER COMPONENT SELECTION
D1
20V, 2A
V
IN
5V
R
GATE
6.04k
R
FAULT
100k
R
FB
130k
R
T
43.2k
C
IN
4.7µF
L1
1.5µH
C
C
1nF
C
OUT2
4.7µF
3581 F05
C
SS
0.1µF
R
C
10.5k
C
OUT1
4.7µF
V
OUT
12V
I
OUT
< 0.83A
SW1 SW2
FB
CLKOUT
GATE
V
C
SS
V
IN
RT
GND
SYNC
FAULT
SHDN
LT3581
C
F
56pF
OPTIONAL
PMOS
The LT3581 can be configured as a Boost converter as
in Figure 5. This topology allows for positive output volt-
ages that are higher than the input voltage. An external
PMOS (optional) driven by the GA
TE pin of the L
T3581 can
achieve input or output disconnect during a fault event.
A single feedback resistor sets the output voltage. For
output voltages higher than 40V, see the Charge Pump
Aided Regulators section.
Table 1 is a step-by-step set of equations to calculate
component values for the LT3581 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.
V
ariable Definitions:
V
IN
= Input Voltage
V
OUT
= Output Voltage
DC = Power Switch Duty Cycle
f
OSC
= Switching Frequency
I
OUT
= Maximum Average Output Current
I
RIPPLE
= Inductor Ripple Current
R
DSON_PMOS
= R
DSON
of External PMOS (set to 0 if not
using PMOS)
Table 1. Boost Design Equations
PARAMETERS/EQUATIONS
Step 1:
Inputs
Pick 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
– 0.3V
( )
• DC
f
OSC
•1A
L
MIN
=
V
IN
– 0.3V
( )
• 2 • DC – 1
( )
2.2A • f
OSC
• 1– DC
( )
L
MAX
=
V
IN
– 0.3V
( )
• DC
f
OSC
• 0.35A
(1)
(2)
(3)
• Pick L1 out of a range of inductor values where the minimum
value of the range is set by L
TYP
or L
MIN
, whichever is higher.
The maximum value of the range is set by L
MAX
. See appendix
on how to choose current rating for inductor value chosen.
Step 4:
I
RIPPLE
I
RIPPLE
=
V
IN
– 0.3V
( )
•
DC
f
OSC
• L
1
Step 5:
I
OUT
I
OUT
= 3.3A –
I
RIPPLE
2
• 1– DC
( )
Step 6:
D1
V
R
> V
OUT
; I
AVG
> I
OUT
Step 7:
C
OUT1
,
C
OUT2
C
OUT1
= C
OUT2
≥
I
OUT
• DC
f
OSC
0.01• V
OUT
– 0.50• I
OUT
• R
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
≥ C
VIN
+ C
PWR
≥
3.3A •DC
45 • f
OSC
• 0.005 • V
IN
+
I
RIPPLE
8 • f
OSC
•0.005• V
IN
• Refer to Input Capacitor Selection in Appendix for definition of
C
VIN
and C
PWR
.
Step 9:
R
FB
R
FB
=
V
OUT
– 1.215V
83.3µA
Step 10:
R
T
R
T
=
87.6
f
OSC
–1; f
OSC
inMHz 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, R
GATE
and
picking appropriae UVLO components.
Note 1: The maximum design target for peak switch current is 3.3A and is
used in this table.
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.
LT3581
14
3581fb
For more information www.linear.com/LT3581
APPLICATIONS INFORMATION
Figure 6. SEPIC Converter – The Component Values and Voltages
Given Are Typical Values for a 700kHz, Wide Input Range (3V to
16V) SEPIC Converter with 5V Out
SEPIC CONVERTER COMPONENT SELECTION
(COUPLED OR UN-COUPLED INDUCTORS)
The LT3581 can also be configured as a SEPIC as shown in
Figure 6. This topology allows for positive output voltages
that are lower, equal, or higher than the input voltage. Out
-
put disconnect is inherently built into the SEPIC topology,
meaning no DC path exists between the input and output
due to capacitor C1. This implies that a PMOS controlled
by the GATE pin is not required in the power path.
Table 2 is a step-by-step set of equations to calculate
component values for the LT3581 when operating as a
SEPIC 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 2.
V
ariable Definitions:
V
IN
= Input Voltage
V
OUT
= Output Voltage
DC = Power Switch Duty Cycle
f
OSC
= Switching Frequency
I
OUT
= Maximum Average Output Current
I
RIPPLE
= Inductor Ripple Current
Table 2. SEPIC Design Equations
PARAMETERS/EQUATIONS
Step 1:
Inputs
Pick V
IN
, V
OUT
, and f
OSC
to calculate equations below.
Step 2:
DC
D
C ≅
V
OUT
+ 0.5V
V
IN
+V
OUT
+ 0.5V – 0.3V
Step 3:
L
L
TYP
=
V
IN
– 0.3V
( )
• DC
f
OSC
•1A
L
MIN
=
V
IN
– 0.3V
( )
• 2 • DC – 1
( )
2.2A • f
OSC
• 1– DC
( )
L
MAX
=
V
IN
– 0.3V
( )
• DC
f
OSC
• 0.35A
(1)
(2)
(3)
• Pick L out of a range of inductor values where the minimum
value of the range is set by L
TYP
or L
MIN
, whichever is higher.
The maximum value of the range is set by L
MAX
. See
Appendix on how to choose current rating for inductor value
chosen.
• Pick L1 = L2 = L for coupled inductors.
• Pick L1L2 = L for un-coupled inductors.
Step 4:
I
RIPPLE
I
RIPPLE
=
V
IN
– 0.3V
( )
• DC
f
OSC
• L
• L = L1 = L2 for coupled inductors.
• L = L1L2 for un-coupled inductors.
Step 5:
I
OUT
I
OUT
= 3.3A –
I
RIPPLE
2
• 1– DC
( )
Step 6:
D1
V
R
> V
IN
+V
OUT
; I
AVG
> I
OUT
Step 7:
C1
C1 ≥ 1µF; V
RATING
≥ V
IN
Step 8:
C
OUT
C
OUT
≥
I
OUT
• DC
f
OSC
•0.005• V
OUT
Step 9:
C
IN
C
IN
≥ C
VIN
+ C
PWR
≥
3.3A •DC
45 • f
OSC
• 0.005 • V
IN
+
I
RIPPLE
8 • f
OSC
•0.005• V
IN
• Refer to Input Capacitor Selection in Appendix for definition
of C
VIN
and C
PWR
.
Step 10:
R
FB
R
FB
=
V
OUT
– 1.215V
83.3µA
Step 11:
R
T
R
T
=
87.6
f
OSC
–1; f
OSC
inMHz andR
T
in kΩ
Note 1: The maximum design target for peak switch current is 3.3A and is
used in this table.
Note 2: The final values for C
OUT
, C
IN
and C1 may deviate from the above
equations in order to obtain desired load transient performance.
D1
30V, 2A
V
IN
3V TO 16V
R
FAULT
100k
R
T
124k
L1
3.3µH
3581 F06
C
SS
1µF
C
OUT
22µF
×2
L2
3.3µH
C
IN
22µF
V
OUT
5V
I
OUT
< 0.9A (V
IN
= 3V)
I
OUT
< 1.5A (V
IN
= 12V)
SW1 SW2
FB
CLKOUT
GATE
V
C
SS
V
IN
RT
GND
SYNC
FAULT
SHDN
ENABLE
LT3581
C
F
100pF
C1
1µF
R
FB
45.3k
•
•
C
C
2.2nF
R
C
7.87k
LT3581
15
3581fb
For more information www.linear.com/LT3581
Due to its unique FB pin, the LT3581 can work in a Dual
Inductor Inverting configuration as in Figure 7. Changing
the connections of L2 and the Schottky diode in the SEPIC
topology results in generating negative output voltages.
This solution results in very low output voltage ripple
due to inductor L2 being in series with the output. Output
disconnect is inherently built into this topology due to the
capacitor C1.
Table 3 is a step-by-step set of equations to calculate
component values for the LT3581 when operating as a
dual inductor inverting converter. Input parameters are
input and output voltage, and switching frequency (V
IN
,
V
OUT
and f
OSC
respectively). Refer to the Appendix for
further information on the design equations presented
in Table 3.
Variable Definitions:
V
IN
= Input Voltage
V
OUT
= Output Voltage
DC = Power Switch Duty Cycle
f
OSC
= Switching Frequency
I
OUT
= Maximum Average Output Current
I
RIPPLE
= Inductor Ripple Current
APPLICATIONS INFORMATION
Figure 7. Dual Inductor Inverting Converter – The Component
Values and Voltages Given Are Typical Values for a 2MHz, 5V to
–12V Inverting Topology Using Coupled Inductors
DUAL INDUCTOR INVERTING CONVERTER COMPONENT
SELECTION (COUPLED OR UN-COUPLED INDUCTORS)
Table 3. Dual Inductor Inverting Design Equations
PARAMETERS/EQUATIONS
Step 1: Inputs Pick V
IN
, V
OUT
, and f
OSC
to calculate equations below.
Step 2: DC
D
C ≅
|V
OUT
| + 0.5V
V
IN
+| V
OUT
|+0.5V – 0.3V
Step 3: L
L
TYP
=
V
IN
– 0.3V
( )
• DC
f
OSC
•1A
L
MIN
=
V
IN
– 0.3V
( )
• 2 • DC – 1
( )
2.2A • f
OSC
• 1– DC
( )
L
MAX
=
V
IN
– 0.3V
( )
• DC
f
OSC
• 0.35A
(1)
(2)
(3)
• Pick L out of a range of inductor values where the
minimum value of the range is set by L
TYP
or L
MIN
,
whichever is higher. The maximum value of the range
is set by L
MAX
. See Appendix on how to choose current
rating for inductor value chosen.
• Pick L1 = L2 = L for coupled inductors.
• Pick L1L2 = L for un-coupled inductors.
Step 4: I
RIPPLE
I
RIPPLE
=
V
IN
– 0.3V
( )
• DC
f
OSC
• L
• L = L1 = L2 for coupled inductors.
• L = L1L2 for un-coupled inductors.
Step 5: I
OUT
I
OUT
= 3.3A –
I
RIPPLE
2
• 1– DC
( )
Step 6: D1
V
R
> V
IN
+ |V
OUT
|; I
AVG
> I
OUT
Step 7: C1
C1
≥
1µF; V
RATING
≥
V
IN
+
|V
OUT
|
Step 8: C
OUT
C
OUT
≥
I
RIPPLE
8 • f
OSC
0.005 • | V
OUT
|
( )
Step 9: C
IN
C
IN
≥ C
VIN
+ C
PWR
≥
3.3A •DC
45 • f
OSC
• 0.005 • V
IN
+
I
RIPPLE
8 • f
OSC
•0.005• V
IN
• Refer to Input Capacitor Selection in Appendix for
definition of C
VIN
and C
PWR
.
Step 10: R
FB
R
FB
=
|V
OUT
| + 5mV
83.3µA
Step 11: R
T
R
T
=
87.6
f
OSC
–1; f
OSC
inMHz andR
T
in kΩ
Note 1: The maximum design target for peak switch current is 3.3A and is
used in this table.
Note 2: The final values for C
OUT
, C
IN
and C1 may deviate from the above
equations in order to obtain desired load transient performance.
L2
3.3µH
D1
20V
1A
V
IN
5V
R
FAULT
100k
R
T
43.2k
L1
3.3µH
3581 F07
C
SS
100nF
C
OUT
4.7µF
C
IN
3.3µF
V
OUT
–12V
I
OUT
< 625mA
SW1 SW2
FB
CLKOUT
GATE
V
C
SS
V
IN
RT
GND
SYNC
FAULT
SHDN
ENABLE
LT3581
C
F
47pF
R
FB
143k
•
•
C
C
1nF
R
C
11k
C1
1µF
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36

LT3581EMSE#TRPBF

Mfr. #:
Buy LT3581EMSE#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 3A Boost/Inverting DC/DC Converter with Fault Protection
Lifecycle:
New from this manufacturer.
Delivery:
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