參數(shù)資料
型號(hào): LTC3851EMSE-1#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PDSO16
封裝: 0.150 INCH, LEAD FREE, PLASTIC, MSOP-16
文件頁數(shù): 17/28頁
文件大?。?/td> 337K
代理商: LTC3851EMSE-1#TRPBF
LTC3851-1
24
38511f
A 4.7μH inductor will produce 28% ripple current and
a 3.3μH will result in 40%. The peak inductor current
will be the maximum DC value plus one-half the ripple
current, or 6A, for the 3.3μH value. Increasing the ripple
current will also help ensure that the minimum on-time
of 90ns is not violated. The minimum on-time occurs at
maximum VIN:
t
V
Vf
V
VkHz
ON MIN
OUT
IN MAX
()
.
=
()
=
()
=
1 8
22
250
327
7ns
The RSENSE resistor value can be calculated by using the
maximum current sense voltage specication with some
accommodation for tolerances.
R
mV
A
SENSE ≤=
50
6
00083
.
Ω
Choosing 1% resistors: R1 = 25.5k and R2 = 32.4k yields
an output voltage of 1.816V.
The power dissipation on the topside MOSFET can be easily
estimated. Choosing a Fairchild FDS6982S dual MOSFET
results in: RDS(ON) = 0.035Ω/0.022Ω, CMILLER = 215pF. At
maximum input voltage with T (estimated) = 50°C:
P
V
CC
MAIN =
() +() ° °
()
1 8
22
5
1
0 005 50
25
0
2
.
..
.
035
22
5
2
215
1
52 3
2
ΩΩ
()+()
()(
)
+
V
A
pF
1
23
250
185
.
() =
kHz
mW
APPLICATIONS INFORMATION
A short-circuit to ground will result in a folded back cur-
rent of:
I
mV
ns
V
μH
SC =
()
=
29
0 0125
1
2
90
22
33
202
.
.
Ω
A
with a typical value of RDS(ON) and δ = (0.005/°C)(25°C)
= 0.125. The resulting power dissipated in the bottom
MOSFET is:
P
V
AmW
SYNC =
() (
)(
) =
22
2 02
1 125 0 022
101 0
2
..
.
Ω
which is less than under full-load conditions.
CIN is chosen for an RMS current rating of at least 3A at
temperature. COUT is chosen with an ESR of 0.02Ω for
low output ripple. The output ripple in continuous mode
will be highest at the maximum input voltage. The output
voltage ripple due to ESR is approximately:
VORIPPLE = RESR (ΔIL) = 0.02Ω (2A) = 40mVP-P
相關(guān)PDF資料
PDF描述
LTC3851EUD-1#TRPBF SWITCHING CONTROLLER, PQCC16
LTCEMSE-1#PBF SWITCHING CONTROLLER, PDSO16
LTC3851IUD-1#TRPBF SWITCHING CONTROLLER, PQCC16
LTC3859IUHF#TRPBF SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PQCC38
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