参数资料
型号: LT3579EUFD-1#TRPBF
厂商: Linear Technology
文件页数: 14/40页
文件大小: 0K
描述: IC REG MULTI CONFIG SYNC 20QFN
标准包装: 2,500
类型: 升压(升压),反相,回扫,Sepic
输出数: 1
输入电压: 2.5 V ~ 16 V
PWM 型: 电流模式
频率 - 开关: 200kHz ~ 2.5MHz
电流 - 输出: 6A
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 20-WFQFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 20-QFN 裸露焊盘(5x4)
LT3579/LT3579-1
APPLICATIONS INFORMATION
SEPIC CONVERTER COMPONENT SELECTION
– COUPLED OR UN-COUPLED INDUCTORS
Table 2. SEPIC Design Equations
PARAMETERS/EQUATIONS
V OUT + 0.5V
V OUT + 0.5V – 0.27V
V IN +
V PWR
9V TO 16V
L1
6.8μH
C PWR
4.7μF
C1
4.7μF
D1
60V, 3A
L2
6.8μH
R FB
130k
V OUT
12V
1.6A (V PWR >9V)
1.9A (V PWR >12V)
Step 1:
Inputs
Step 2: DC
Pick V IN , V OUT , and f OSC to calculate equations below.
DC ?
SW1 SW2 C OUT
V IN
V IN
3.3V
FB
100k
V C
RT
R C
R T
9.53k
86.6k C SS
C C
2.2nF
( V IN – 0.27V ) ? DC
L TYP =
( V IN – 0.27V ) ? ( 2 ? DC – 1 )
4A ? f OSC ? ( 1 – DC )
( V IN – 0.27V ) ? DC
( V IN – 0.27V ) ? DC
f OSC ? L
I OUT = ? 6A – RIPPLE ? ? ( 1 – DC )
C PWR =
C VIN =
10μF
TO 5V × 3
SHDN GATE
LT3579
C VIN FAULT CLKOUT
4.7μF
C F
SYNC GND SS 47pF
0.22μF
35791 F07
Figure 7. SEPIC Converter – The Component Values Given Are
Typical Values for a 1MHz, 9V–16V to 12V SEPIC Topology Using
Coupled Inductors
The LT3579 can also be configured as a SEPIC as in
Figure 7. This topology allows for positive output voltages
that are lower, equal, or higher than the input voltage. 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
SEPIC converter using coupled inductors. 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 2.
Variable Definitions:
Step 3: L
Step 4:
I RIPPLE
Step 5: I OUT
Step 6: D1
Step 7: C1
Step 8: C OUT
Step 9: C PWR
Step 10: C VIN
(1)
f OSC ? 1.8A
L MIN = (2)
L MAX = (3)
f OSC ? 0.5A
? Solve equations 1, 2, and 3.
? Choose the higher value between L TYP and L MIN for L.
L should never exceed L MAX .
? L = L1 = L2 for coupled inductors.
? L = L1 ?? L2 for un-coupled inductors.
I RIPPLE =
? I ?
? 2 ?
V R > V IN + V OUT ; I AVG > I OUT
4.7μF (typical) ; V RATING > V IN
I OUT ? DC
C OUT =
f OSC ? 0.005 ? V OUT
I RIPPLE
8 ? f OSC ? 0.005 ? V IN
6A ? DC
40 ? f OSC ? 0.005 ? V IN
R FB =
Step 11: R FB
R T =
– 1; f OSC in MHz and R T in k ?
f OSC
V IN =InputVoltage
V OUT = Output Voltage
DC = Power Switch Duty Cycle
f OSC = Switching Frequency
I OUT = Maximum Output Current
I RIPPLE = Inductor Ripple Current
V OUT – 1.215V
83.3μA
87.6
Step 12: R T
Note: The maximum design target for peak switch current is 6A and
is used in this table. The final values for C OUT , C PWR , and C VIN may
deviate from the above equations in order to obtain desired load
transient performance for a particular application.
35791f
14
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