参数资料
型号: LT3579EFE-1#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: SWITCHING REGULATOR, PDSO20
封装: 4.40 MM, LEAD FREE, PLASTIC, TSSOP-20
文件页数: 6/40页
文件大小: 503K
代理商: LT3579EFE-1#PBF
LT3579/LT3579-1
14
35791f
applicaTions inForMaTion
Figure 7. SEPIC Converter – The Component Values Given Are
Typical Values for a 1MHz, 9V–16V to 12V SEPIC Topology Using
Coupled Inductors
SEPIC CONVERTER COMPONENT SELECTION
– COUPLED OR UN-COUPLED INDUCTORS
The LT3579 can also be configured as a SEPIC as in
Figure 7. This topology allows for positive output voltages
thatarelower,equal,orhigherthantheinputvoltage.Output
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 LT3579 when operating as a
SEPICconverterusingcoupledinductors.Inputparameters
are input and output voltage, and switching frequency
(VIN, VOUT and fOSC respectively). Refer to the Appendix
for further information on the design equations presented
in Table 2.
Variable Definitions:
VIN = Input Voltage
VOUT = Output Voltage
DC = Power Switch Duty Cycle
fOSC = Switching Frequency
IOUT = Maximum Output Current
IRIPPLE = Inductor Ripple Current
Table 2. SEPIC Design Equations
PARAMETERS/EQUATIONS
Step 1:
Inputs
Pick VIN, VOUT, and fOSC to calculate equations below.
Step 2: DC
DC
VOUT + 0.5V
VIN + VOUT + 0.5V – 0.27V
Step 3: L
LTYP =
VIN – 0.27V
(
) DC
fOSC 1.8A
LMIN =
VIN – 0.27V
(
) 2 DC – 1
(
)
4A
fOSC 1 – DC
(
)
LMAX =
VIN – 0.27V
(
) DC
fOSC 0.5A
(1)
(2)
(3)
Solve equations 1, 2, and 3.
Choose the higher value between LTYP and LMIN for L.
L should never exceed LMAX.
L = L1 = L2 for coupled inductors.
L = L1
L2 for un-coupled inductors.
Step 4:
IRIPPLE
IRIPPLE =
VIN – 0.27V
(
)DC
fOSC L
Step 5: IOUT
IOUT = 6A –
IRIPPLE
2
1– DC
(
)
Step 6: D1
VR > VIN + VOUT ;IAVG > IOUT
Step 7: C1
4.7F (typical) ; VRATING > VIN
Step 8: COUT
COUT =
IOUT DC
fOSC 0.005 VOUT
Step 9: CPWR
CPWR =
IRIPPLE
8
fOSC 0.005 VIN
Step 10: CVIN
CVIN =
6A
DC
40
fOSC 0.005 VIN
Step 11: RFB
RFB =
VOUT – 1.215V
83.3A
Step 12: RT
RT =
87.6
fOSC
–1; fOSC in MHz andRT in k
Note: The maximum design target for peak switch current is 6A and
is used in this table. The final values for COUT, CPWR, and CVIN may
deviate from the above equations in order to obtain desired load
transient performance for a particular application.
VPWR
9V TO 16V
RT
86.6k
100k
COUT
10F
×3
CPWR
4.7F
RFB
130k
CF
47pF
CSS
0.22F
CVIN
4.7F
L1
6.8H
D1
60V, 3A
C1
4.7F
SW1 SW2
GATE
VIN
RT
VC
CC
2.2nF
RC
9.53k
FAULT
SHDN
FB
SS
GND
SYNC
CLKOUT
LT3579
35791 F07
VOUT
12V
1.6A (VPWR >9V)
1.9A (VPWR >12V)
L2
6.8H
VIN
3.3V
TO 5V
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