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| 型号： | LTC3727AIG-1#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 5.30 MM, LEAD FREE, PLASTIC, SSOP-28 |
| 文件页数： | 17/32页 |
| 文件大小： | 328K |
| 代理商： | LTC3727AIG-1#TRPBF |
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LTC3727A-1
24
3727a1fa
automobile is the source of a number of nasty potential
transients, including load-dump, reverse-battery, and
double-battery.
Load-dump is the result of a loose battery cable. When the
cable breaks connection, the eld collapse in the alterna-
tor can cause a positive spike as high as 60V which takes
several hundred milliseconds to decay. Reverse-battery is
just what it says, while double-battery is a consequence of
tow-truck operators nding that a 24V jump start cranks
cold engines faster than 12V.
The network shown in Figure 9 is the most straight for-
ward approach to protect a DC/DC converter from the
ravages of an automotive power line. The series diode
prevents current from owing during reverse-battery,
while the transient suppressor clamps the input voltage
during load-dump. Note that the transient suppressor
should not conduct during double-battery operation, but
must still clamp the input voltage below breakdown of
the converter. Although the LTC3727A-1 has a maximum
input voltage of 36V, most applications will be limited to
30V by the MOSFET BVDSS.
Design Example
As a design example for one channel, assume VIN =
24V(nominal), VIN = 30V(max), VOUT = 12V, IMAX = 5A
and f = 250kHz.
The inductance value is chosen rst based on a 40% ripple
current assumption. The highest value of ripple current
occurs at the maximum input voltage. Tie the PLLFLTR
pin to the SGND pin for 250kHz operation. The minimum
inductance for 40% ripple current is:
ΔI
V
fL
V
L
OUT
IN
=
()( )
–
1
A 14μH inductor will result in 40% ripple current. The peak
inductor current will be the maximum DC value plus one
half the ripple current, or 6A, for the 14μH value.
APPLICATIONS INFORMATION
The RSENSE resistor value can be calculated by using the
maximum current sense voltage specication with some
accommodation for tolerances:
R
mV
A
SENSE
≤≈
Ω
90
6
0 015
.
Choosing 1% resistors; R1 = 20k and R2 = 280k yields
an output voltage of 12V.
The power dissipation on the top side MOSFET can be
easily estimated. Choosing a Siliconix Si4412DY results
in: RDS(ON) = 0.042Ω, CRSS = 100pF. At maximum input
voltage with T(estimated) = 50°C:
P
V
CC
MAIN =
() +°
°
[]
12
30
5
1
0 005 50
25
0 042
2
(.
)(
–
)
.
Ω
()+ () ( )(
)(
)
=
1 7 30
5
100
250
664
2
.V
A
pF
kHz
mW
A short-circuit to ground will result in a folded back
current of:
I
mV
ns
V
μH
A
SC =
Ω
+
=
45
0 015
1
2
200
30
14
32
.
()
.
with a typical value of RDS(ON) and δ = (0.005/°C)(20) = 0.1.
The resulting power dissipated in the bottom MOSFET is:
P
VV
V
A
mW
SYNC =
() ( )
Ω
()
=
30
12
30
32
11 0042
284
2
–
..
.
which is less than under full-load conditions.
Figure 9. Automotive Application Protection
VIN
3727 F09
LTC3727A-1
TRANSIENT VOLTAGE
SUPPRESSOR
GENERAL INSTRUMENT
1.5KA24A
50A IPK RATING
12V
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| LTC3727AIG-1#PBF | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO28 |
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| LTC3727EG | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3727EG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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