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| 型号： | LTC1438XCG |
| 厂商： | Linear Technology |
| 文件页数： | 22/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-SSOP |
| 标准包装： | 47 |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 138kHz |
| 占空比： | 99% |
| 电源电压： | 3.5 V ~ 30 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： | 0°C ~ 70°C |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 包装： | 管件 |
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LTC1438/LTC1439
APPLICATIO N S I N FOR M ATIO N
? I L = OUT ? 1 – OUT ?
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
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 :
V ? V ?
( f )( L ) ? V IN ?
The highest value of the ripple current occurs at the
maximum input voltage:
? 1 –
? = 1 . 12 A
cablebreaksconnection,thefieldcollapseinthealternator
can cause a positive spike as high as 60V which takes
several hundred milliseconds to decay. Reverse battery is
? I L =
3 . 3 V ?
250 kHz ( 10 μ H ) ?
3 . 3 V ?
22 V ?
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
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:
[
]
( ) 3 1 + ( ) ( ) ( )
0 . 005 50 ° C ? 25 ° C
0 . 042 ?
ravages of an automotive battery line. The series diode
prevents current from flowing during reverse battery,
P MAIN =
3 .3V
22 V
2
+ 2 . 5 ( 22 V )
while the transient suppressor clamps the input voltage
during load dump. Note that the transient suppressor
1 . 85
( 3 A )( 100 pF )( 250 kHz ) = 122 mW
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 .
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)
12V
50A IPK RATING
V IN
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.
TRANSIENT VOLTAGE
SUPPRESSOR
GENERAL INSTRUMENT
1.5KA24A
LTC1438
LTC1439
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
1438 F12
Figure 12. Automotive Application Protection
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
14389fb
22
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参数描述 |
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| LTC1438XCG#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:- 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 |
| LTC1438XCG#TR | 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:- 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 |
| LTC1438XCG#TRPBF | 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:- 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 |
| LTC1439CG | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC1439CG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
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