參數(shù)資料
型號(hào)： LTC1438
廠商： Linear Technology Corporation
元件分類： 基準(zhǔn)電壓源/電流源
英文描述： Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators
中文描述： 雙通道高效率，低噪聲，同步降壓型開關(guān)穩(wěn)壓器
文件頁(yè)數(shù)： 22/32頁(yè)
文件大?。?/td> 596K
代理商： LTC1438
22
LTC1438/LTC1439
Design Example
As a design example, assume V
IN
= 12V(nominal), V
IN
=
22V(max), V
OUT
= 3.3V, I
MAX
= 3A and f = 250kHz, R
SENSE
and C
OSC
can immediately be calculated:
R
SENSE
= 100mV/3A = 0.033
C
OSC
= [1.37(10
4
)/250] – 11
≈
43pF
Refering to Figure 3, a 10
μ
H inductor falls within the
recommended range. To check the actual value of the
ripple current the following equation is used :
I
V
( )( )
f L
V
V
L
OUT
OUT
IN
=
–
1
The highest value of the ripple current occurs at the
maximum input voltage:
I
V
10
(
kHz
H
V
V
A
L
=
μ
=
3 3
.
250
1
3 3
22
1 12
.
)
–
.
The power dissipation on the topside MOSFET can be
easily estimated. Using a Siliconix Si4412DY for example;
R
DS(ON)
= 0.042
, C
RSS
= 100pF. At maximum input
voltage with T(estimated) = 50
°
C:
P
V
V
C
C
V
A
pF
kHz
mW
MAIN
=
( )
3
+
(
(
3
°
°
)
[
]
(
)
+
)
)(
)(
)
=
3 3
22
2 5 22
.
1
0 005 50
.
25
0 042
.
100
250
122
2
1 85
.
.
The most stringent requirement for the synchronous
N-channel MOSFET is with V
OUT
= 0V (i.e. short circuit).
During a continuous short circuit, the worst-case dissipa-
tion rises to:
P
SYNC
= [I
SC(AVG)
]
2
(1 +
δ
)R
DS(ON)
With the 0.033
sense resistor I
SC(AVG)
= 4A will result,
increasing the Si4412DY dissipation to 950mW at a die
temperature of 105
°
C.
C
IN
will require an RMS current rating of at least 1.5A at
temperature and C
OUT
will require an ESR of 0.03
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:
V
ORIPPLE
= R
ESR
(
I
L
) = 0.03
(1.12A) = 34mV
P-P
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25)(C
LOAD
).
Thus a 10
μ
F capacitor would require a 250
μ
s rise time,
limiting the charging current to about 200mA.
Automotive Considerations: Plugging into the
Cigarette Lighter
As battery-powered devices go mobile, there is a natural
interest in plugging into the cigarette lighter in order to
conserve or even recharge battery packs during operation.
But before you connect, be advised: you are plugging into
the supply from hell. The main battery line in an automo-
bile 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 field collapse in the alternator
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 finding that a 24V jump start cranks
cold engines faster than 12V.
The network shown in Figure 12 is the most straightfor-
ward approach to protect a DC/DC converter from the
ravages of an automotive battery line. The series diode
prevents current from flowing 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 LT1438/LT1439 has a maximum
input voltage of 36V, most applications will be limited to
30V by the MOSFET BV
DSS
.
APPLICATIO
S I
N
FOR
ATIO
U
W
U
1438 F12
50A IPK RATING
LTC1438
LTC1439
TRANSIENT VOLTAGE
SUPPRESSOR
GENERAL INSTRUMENT
1.5KA24A
V
IN
12V
Figure 12. Automotive Application Protection
相關(guān)PDF資料
PDF描述
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參數(shù)描述
LTC1438CG 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1438CG#PBF 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1438CG#TR 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
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