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参数资料
| 型号： | LTC3775EUD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/34页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 16-QFN |
| 标准包装： | 121 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 80% |
| 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 ~ 85°C |
| 封装/外壳： | 16-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3775
APPLICATIONS INFORMATION
The value of Q G should come from the plot of V GS vs
Q G in the Typical Performance Characteristics section of
the MOSFET data sheet. The value listed in the electrical
speci?cations may be measured at a higher V GS , such
as 10V, whereas the value of interest is at the 5V INTV CC
gate drive voltage.
Care must be taken to ensure that the maximum junction
temperature of the LTC3775 is never exceeded. The junc-
tion temperature can be estimated using the following
equations:
P DISS = V IN ? I INTVCC
T J = T A + P DISS ? R TH(JA)
As an example of the required thermal analysis, consider
a buck converter with a 24V input voltage and an output
voltage of 3.3V at 15A. The switching frequency is 500kHz
and the maximum ambient temperature is 70°C. The power
MOSFET used for this application is the Vishay Siliconix
Si7884DP, which has a typical R DS(ON) of 7.5mΩ at V GS
= 4.5V and 5.5mΩ at V GS = 10V. From the plot of V GS vs
Q G , the total gate charge at V GS = 5V is 18.5nC (the tem-
perature coef?cient of the gate charge is low). One power
MOSFET is used for the top side and one for the bottom
side. For the UD package:
I INTVCC = 3.5mA + 2 ? 18.5nC ? 500kHz = 22mA
P DISS = 24V ? 22mA = 528mW
T J = 70°C + 528mW ? 68°C/W = 105.9°C
Finally, it is important to verify the calculations by perform-
ing a thermal analysis of the ?nal PCB using an infrared
camera or thermal probe.
Operation at Low Supply Voltage
The LTC3775 has a minimum input voltage of 4.5V. The
gate driver for the LTC3775 consists of a PMOS pull-up
and an NMOS pull-down device, allowing the full INTV CC
voltage to be applied to the gates during power MOSFET
switching. Nonetheless, care should be taken to deter-
mine the minimum gate drive supply voltage (INTV CC ) in
order to choose the optimum power MOSFETs. Important
parameters that can affect the minimum gate drive volt-
age are the minimum input voltage (V IN(MIN) ), the LDO
dropout voltage, the Q G of the power MOSFETs, and the
operating frequency.
If the input voltage V IN is low enough for the INTV CC LDO
to be in dropout, then the minimum gate drive supply
voltage is:
V INTVCC = V IN(MIN) – V DROPOUT
The LDO dropout voltage is a function of the total gate
drive current and the quiescent current of the IC (typically
3.5mA). A curve of dropout voltage versus output cur-
rent for the LDO is shown in Figure 10. The temperature
coef?cient of the LDO dropout voltage is approximately
6000ppm/°C. See the INTV CC Regulator and Thermal
Considerations sections for information about calculating
the total quiescent current.
In this example, the junction temperature rise is 35.9°C.
These equations demonstrate how the gate charge cur-
rent typically dominates the quiescent current of the IC,
and how the choice of the operating frequency and board
heat sinking can have a signi?cant effect on the thermal
performance of the solution.
To prevent the maximum junction temperature from be-
ing exceeded, the input supply current of the IC should
be checked when operating in continuous mode (heavy
0
–0.2
–0.4
–0.6
–0.8
T A = 25°C
load) at maximum V IN . A trade-off between the operat-
ing frequency and the size of the power MOSFETs may
need to be made in order to maintain a reliable junction
–1.0
0
10 20 30 40
INTV CC LOAD CURRENT (mA)
50
3775 F10
temperature.
Figure 10. INTV CC LDO Dropout Voltage vs Current
3775fa
17
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| LTC3775IMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-MSOP 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:2,500 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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| LTC3775IUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-QFN 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:2,500 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) |
| LTC3776EGN | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Sync Step Down 2.75V to 9.8V Input 24-Pin SSOP N |
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