参数资料
型号: LT3579EFE#PBF
厂商: Linear Technology
文件页数: 15/40页
文件大小: 0K
描述: IC REG MULTI CONFIG SYNC 20TSSOP
标准包装: 74
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-TSSOP(0.173",4.40mm 宽)裸露焊盘
包装: 管件
供应商设备封装: 20-TSSOP-EP
LT3579/LT3579-1
APPLICATIONS INFORMATION
DUAL INDUCTOR INVERTING CONVERTER COMPONENT
SELECTION – COUPLED OR UN-COUPLED INDUCTORS
Table 3. Dual Inductor Inverting Design Equations
PARAMETERS/EQUATIONS
| V OUT | + 0.5V
V IN + | V OUT | + 0.5V – 0.27V
( 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
5V
C IN
22μF
R T
72k
L1
3.3μH
V IN
SHDN
100k
FAULT
RT
SYNC
C1
4.7μF
SW1 SW2
FB
GATE
LT3579
CLKOUT
V C
GND SS
C SS
0.22μF
L2
3.3μH
D1
30V, 2A
C F
27pF
R FB
144k
R C
20k
C C
1nF
35791 F08
V OUT
–12V
1.2A
C OUT
10μF
× 2
Step 1: Inputs
Step 2: DC
Step 3: L
Pick V IN , V OUT , and f OSC to calculate equations belo w.
DC ?
(1)
f OSC ? 1.8A
L MIN = (2)
L MAX = (3)
f OSC ? 0.5A
? Solve equations 1, 2, and 3.
Figure 8. Dual Inductor Inverting Converter – The Component
Values Given Are Typical Values for a 1.2MHz, 5V to –12V Inverting
Topology Using Coupled Inductors
? 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.
( V IN – 0.27V ) ? DC
f OSC ? L
I OUT = ? 6A – RIPPLE ? ? ( 1 – DC )
C OUT =
C IN =
I RIPPLE 6A ? DC
8 ? f OSC ? 0.005 ? V IN
40 ? f OSC ? 0.005 ? V IN
| V OUT | + 9mV
R FB =
DuetoitsuniqueFBpin,theLT3579canworkinaDual
Inductor Inverting configuration as in Figure 8. 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 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 LT3579 when operating as a Dual
Inductor Inverting 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 3.
Variable Definitions:
Step 4: I RIPPLE
Step 5: I OUT
Step 6: D1
Step 7: C1
Step 8: C OUT
Step 9: C IN
Step 10: R FB
I RIPPLE =
? I ?
? 2 ?
V R > V IN + | V OUT | ; I AVG > I OUT
4.7μF (typical) ; V RATING > V IN + | V OUT |
I RIPPLE
8 ? f OSC ? 0.005 ? | V OUT |
C IN = C PWR + C VIN
+
83.3μA
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
87.6
Step 11: 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 and C IN may deviate
from the above equations in order to obtain desired load transient
performance for a particular application.
35791f
15
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