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参数资料
| 型号： | LTC3404MPMS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.6A 8MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.8 V ~ 6 V |
| 输入电压： | 2.65 V ~ 6 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1.4MHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 是 |
| 工作温度： | -55°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-MSOP |
LTC3404
APPLICATIO S I FOR ATIO
very low load currents can be misleading since the actual
power lost is of no consequence as illustrated in Figure 6.
1. The V IN quiescent current is due to two components:
the DC bias current as given in the electrical character-
istics and the internal main switch and synchronous
switch gate charge currents. The gate charge current
results from switching the gate capacitance of the
internal power MOSFET switches. Each time the gate is
switched from high to low to high again, a packet of
1
0.1
0.01
0.001
0.0001
V IN = 4.2V
L = 4.7 μ H
V OUT = 1.5V
V OUT = 2.5V
V OUT = 3.3V
Burst Mode OPERATION
charge dQ moves from V IN to ground. The resulting
0.00001
0.1
1
10 100
1000
dQ/dt is the current out of V IN that is typically larger than
the DC bias current. In continuous mode, I GATECHG =
f(Q T + Q B ) where Q T and Q B are the gate charges of the
internal top and bottom switches. Both the DC bias and
gate charge losses are proportional to V IN and thus
their effects will be more pronounced at higher supply
voltages.
2. I 2 R losses are calculated from the resistances of the
internal switches, R SW , and external inductor R L . In
continuous mode the average output current flowing
through inductor L is “chopped” between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
top and bottom MOSFET R DS(ON) and the duty cycle
(DC) as follows:
R SW = (R DS(ON)TOP )(DC) + (R DS(ON)BOT )(1 – DC)
The R DS(ON) for both the top and bottom MOSFETs can
be obtained from the Typical Performance Charateristics
curves. Thus, to obtain I 2 R losses, simply add R SW to
R L and multiply the result by the square of the average
output current.
Other losses including C IN and C OUT ESR dissipative
losses and inductor core losses generally account for less
than 2% total additional loss.
Thermal Considerations
In most applications the LTC3404 does not dissipate
much heat due to its high efficiency. But, in applications
where the LTC3404 is running at high ambient tempera-
ture with low supply voltage and high duty cycles, such
as in dropout, the heat dissipated may exceed the maxi-
mum junction temperature of the part. If the junction
LOAD CURRENT (mA)
3404 F06
Figure 6. Power Lost vs Load Current
temperature reaches approximately 175 ° C, both power
switches will be turned off and the SW node will become
high impedance.
To avoid the LTC3404 from exceeding the maximum
junction temperature, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated exceeds the
maximum junction temperature of the part. The tempera-
ture rise is given by:
T R = (P D )( θ JA )
where P D is the power dissipated by the regulator and q JA
is the thermal resistance from the junction of the die to the
ambient temperature.
The junction temperature, T J , is given by:
T J = T A + T R
where T A is the ambient temperature.
As an example, consider the LTC3404 in dropout at an
input voltage of 3V, a load current of 500mA, and an
ambient temperature of 70 ° C. From the typical perfor-
mance graph of switch resistance, the R DS(ON) of the
P-channel switch at 70 ° C is approximately 0.7 Ω . There-
fore, power dissipated by the part is:
P D = I LOAD2 ? R DS(ON) = 0.175W
For the MSOP package, the θ JA is 150 ° C/ W. Thus, the
junction temperature of the regulator is:
T J = 70 ° C + (0.175)(150) = 96 ° C
3404fb
12
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相关代理商/技术参数 |
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| LTC3405 | 制造商:LINEAR 制造商全称:LINEAR 功能描述:Standalone 250mA Li-Ion Battery Charger in 2 × 2 DFN |
| LTC3405A | 制造商:LINER 制造商全称:Linear Technology 功能描述:1.5MHz, 300mA Synchronous Step-Down Regulator in ThinSOT |
| LTC3405A-1.375 | 制造商:LINER 制造商全称:Linear Technology 功能描述:1.375V, 1.5MHz, 300mA Synchronous Step-Down Regulators in ThinSOT |
| LTC3405A-1.5 | 制造商:LINER 制造商全称:Linear Technology 功能描述:1.5V, 1.8V, 1.5MHz, 300mA Synchronous Step-Down Regulators in ThinSOT |
| LTC3405A-1.8 | 制造商:LINER 制造商全称:Linear Technology 功能描述:1.5V, 1.8V, 1.5MHz, 300mA Synchronous Step-Down Regulators in ThinSOT |
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