參數(shù)資料
型號: LT3782IFE
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 4 A SWITCHING CONTROLLER, 533 kHz SWITCHING FREQ-MAX, PDSO28
封裝: 4.40 MM, PLASTIC, TSSOP-28
文件頁數(shù): 3/20頁
文件大?。?/td> 223K
代理商: LT3782IFE
LT3782
11
3782fg
The Peak and Average Input Currents
The control circuit in the LT3782 measures the input current
by using a sense resistor in each MOSFET source, so the
output current needs to be reected back to the input in
order to dimension the power MOSFET properly. Based
on the fact that, ideally, the output power is equal to the
input power, the maximum average input current is:
I
IN(MAX) =
I
O(MAX)
1– D
MAX
The peak current is:
I
IN(PEAK) = 1.2
I
O(MAX)
1– D
MAX
The maximum duty cycle, DMAX, should be calculated at
minimum VIN.
Power Inductor Selection
In a boost circuit, a power inductor should be designed
to carry the maximum input DC current. The inductance
should be small enough to generate enough ripple current
to provide adequate signal to noise ratio to the LT3782.
An empirical starting of the inductor ripple current (per
phase) is about 40% of maximum DC current, which is
half of the input DC current in a 2-phase circuit:
ΔI
L 40%
I
OUT(MAX) VOUT
2V
IN
=20%
I
OUT(MAX) VOUT
V
IN
where VIN, VOUT and IOUT are the DC input voltage, output
voltage and output current, respectively.
And the inductance is estimated to be:
L
=
V
IN D
f
s ΔIL
where fs is the switching frequency per phase.
The saturation current level of inductor is estimated to
be:
I
SAT
ΔI
L
2
+
I
IN
2
70%
I
OUT(MAX) VOUT
V
IN(MIN)
Sense Resistor Selection
During the switch on-time, the control circuit limits the
maximum voltage drop across the sense resistor to about
60mV. The peak inductor current is therefore limited to
60mV/R. The relationship between the maximum load
current, duty cycle and the sense resistor RSENSE is:
R
≤ V
SENSE(MAX)
1– D
MAX
1.2
I
O(MAX)
2
Power MOSFET Selection
Important parameters for the power MOSFET include the
drain-to-source breakdown voltage (BVDSS), the threshold
voltage (VGS(TH)), the on-resistance (RDS(ON)) versus gate-
to-source voltage, the gate-to-source and gate-to-drain
charges (QGS and QGD, respectively), the maximum drain
current (ID(MAX)) and the MOSFET’s thermal resistances
(RTH(JC) and RTH(JA)).
APPLICATIONS INFORMATION
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