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| 型号： | LTC3839EUH#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 37/50页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 73 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 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： | 32-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3839
APPLICATIONS INFORMATION
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 LTC3839 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,
for details). 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 individual channel’s 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
R DCR =
=
then the R can be calculated as:
L 0.56μH
DCR ? C DCR 1.8m Ω ? 0.1μF
= 3.1k Ω
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
V RNG =
= 28mV ? 20 = 0.56V
( 15A ) 2 ( 13m Ω ) ?? 1 + 0.4% ( 125 ° C – 25 ° C ) ??
P TOP = ?
+ ( 24V ) ?
? ? ( 150pF ) ? 5.3V – 3V + 3V ? ( 350kHz )
? ? ( 15A ) ( 3.9m Ω ) ?? 1 + 0.4% ( 125 ° C – 25 ° C ) ??
P BOT = ?
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 (5.3V) or RT pin (1.2V) to signal ground
(SGND). To make sure that the maximum load current can
be supplied under all conditions, such as lower INTV CC
due to a lower V IN , and account for the range of IC’s own
V SENSE(MAX) variation within specification, a higher V RNG
should be used to provide margin.
A better and the recommended way to set V RNG is to sim-
ply tie the V RNG pin to SGND for an equivalent of V RNG =
0.6V, while using an additional resistor in the DCR filter,
as discussed in DCR Inductor Current Sensing, to scale
the V SENSE(MAX) down by a comfortable margin below
the lower limit of the IC’s own V SENSE(MAX) specification,
so that the maximum output current can be guaranteed.
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 less than half of the lower
limit of LTC3839’s statistical 2-channel-sum V SENSE(MAX)
typical T J = 125°C:
? 1.2V ?
? 24V ? ?
2 ? 15A ? ? 2.5 Ω 1.2 Ω ?
? 2 ? ?
= 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
These numbers show that careful attention should be paid
to proper heat sinking when operating at higher ambient
temperatures. For higher frequency, higher input voltage,
and/or higher load current applications, the LTC3839 IC’s
junction temperature should be estimated to make sure
the maximum junction temperature rating is not exceeded,
as discussed in the DRV CC Regulator and EXTV CC Power
section.
at V RNG = 0.6V (see Current Limit Programming section
3839fa
37
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| LTC3839IUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-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) |
| LTC3839IUH#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-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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| LTC3850EGN#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: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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