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参数资料
| 型号： | LTC3838IFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 40/54页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 38TSSOP |
| 标准包装： | 50 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 2MHz |
| 电源电压： | 4.5 V ~ 38 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： | 38-TFSOP （0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 管件 |
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LTC3838
APPLICATIONS INFORMATION
Set the inductor value to give 40% ripple current at maxi-
mum V IN using the adjusted operating frequency:
while using an additional resistor in the DCR filter, as
discussed in DCR Inductor Current Sensing, to scale the
L = ?
? ? ? ? 1– 24V ? ? = 0.54μH
? 1.2V
? 350kHz ? 40% ? 15A
? ? 1.2V ?
V SENSE(MAX) down by a comfortable margin below the
lower limit of the LTC3838’s own V SENSE(MAX) specification,
so that the maximum output current can be guaranteed.
? ? ? ? 1– 24V ? ? = 5.8A
Δ I L = ?
R DCR =
=
= 3.1k Ω
V RNG =
= 28mV ? 20 = 0.56V
( 15A ) 2 ( 13m Ω ) ?? 1 + 0.4% ( 125 ° C – 25 ° C ) ??
P TOP = ?
( ) ? ? 5.3V – 3V + 1.2 3V Ω ? ? ( )
+ ( ) ?
2 ? 15A ? 2.5 Ω
? 2 ? ?
? ? ( 15A ) ( 3.9m Ω ) ?? 1 + 0.4% ( 125 ° C – 25 ° C ) ??
P BOT = ?
Select 0.56μH which is the nearest standard value.
The resulting maximum ripple current is:
? 1.2V ? ? 1.2V ?
? 350kHz ? 0.56μH
Often in a high power application, DCR current sensing is
preferred over R SENSE in order to maximize efficiency. In
order to determine the DCR filter values, first the inductor
manufacturer has to be chosen. For this design, the Vishay
IHLP-4040DZ-01 model is chosen with a value of 0.56μH
and a DCR MAX =1.8mΩ. This implies that:
V SENSE(MAX) = 1.8mΩ ? [1 + (100°C – 25°C) ? 0.4%/°C]
? (15A – 5.8A/2) = 28mV
The maximum sense voltage, V SENSE(MAX) , is within the
range that LTC3838 can handle without any additional
scaling. Therefore, the DCR filter can use a simple RC
filter across the inductor. If the C is chosen to be 0.1μF,
then the R can be calculated as:
L 0.56μH
DCR ? C DCR 1.8m Ω ? 0.1μF
The resulting V RNG pin voltage is:
V SENSE(MAX)
0.05
This voltage can be generated with a resistive divider from
the INTV CC pin to signal ground (SGND). To make sure that
the maximum load current of 15A can be supplied under
all conditions, such as lower INTV CC due to a lower V IN ,
and account for the range of LTC3838’s own V SENSE(MAX)
variation within specification, a higher V RNG should be
used to provide margin.
In this design example, a 3.57k and 15k resistor divider is
used. The previously calculated V SENSE(MAX) is scaled down
from 28mV to 22.6mV, which is close to the lower limit of
LTC3838’s V SENSE(MAX) specification at V RNG = 0.6V. Note
the equivalent R DCR = 3.57k//15k = 2.9k, slightly lower
than the 3.1k calculated above for a matched R DCR -C DCR
and L-DCR network. The resulted mismatch allows for a
slightly higher ripple in V SENSE .
Remember to check the peak inductor current, considering
the upper spec limit of V SENSE(MAX) and the DCR (MIN) at
lowest operating temperature, is not going to saturate the
inductor or exceed the rating of power MOSFETs.
For the external N-channel MOSFETs, Renesas
RJK0305DBP (R DS(ON) = 13mΩ max, C MILLER = 150pF, V GS
= 4.5V, θ JA = 40°C/W, T J(MAX) = 150°C) is chosen for the top
MOSFET (main switch). RJK0330DBP (R DS(ON) = 3.9mΩ
max, V GS = 4.5V, θ JA = 40°C/W, T J(MAX) = 150°C) is chosen for
the bottom MOSFET (synchronous switch). The power dis-
sipation for each MOSFET can be calculated for V IN = 24V and
typical T J = 125°C:
? 1.2V ?
? 24V ? ?
24V 150pF 350kHz
? ?
= 0.54W
? 24V – 1.2V ? 2
? 24V
= 1.2W
The resulted junction temperatures at an ambient tem-
perature T A = 75°C are:
T J(TOP) = 75°C + (0.54W)(40°C/W) = 97°C
T J(BOT) = 75°C + (1.2W)(40°C/W) = 123°C
A better and the recommended way to set V RNG is to simply
tie the V RNG pin to SGND for an equivalent of V RNG = 0.6V,
3838fa
40
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| LTC3838IUHF#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN 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:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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