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参数资料
| 型号： | LTC3709EUH#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 2,500 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 200kHz |
| 占空比： | 90% |
| 电源电压： | 5 V ~ 36 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： | 32-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
LTC3709
APPLICATIO S I FOR ATIO
Connecting the SENSE + and SENSE – Pins
The LTC3709 provides the user with an optional method to
sense current through a sense resistor instead of using the
R DS(ON) of the synchronous MOSFET. When using a sense
resistor, it is placed between the source of the synchro-
nous MOSFET and ground. To measure the voltage across
this resistor, connect the SENSE + pin to the source end of
the resistor and the SENSE – pin to the other end of the
2.0
1.5
1.0
0.5
resistor. The SENSE + and SENSE – pin connections pro-
0
– 50
0
50
100
150
D TOP =
= IN OUT
? I OUT ( MAX ) ?
? ?
( 0 . 5 ) ? V IN ? ? OUT ? ? C RSS ? f ?
? ?
+
R DS ( ON )_ DRV ?
?
? ( DRV CC GS ( TH ) ) V GS ( TH ) ?
?
vide the Kelvin connections, ensuring accurate voltage
measurement across the resistor. Using a sense resistor
provides a well-defined current limit, but adds cost and
reduces efficiency. Alternatively, one can use the synchro-
nous MOSFET as the current sense element by simply
connecting the SENSE + pin to the switch node SW and the
SENSE – pin to the source of the synchronous MOSFET,
eliminating the sense resistor. This improves efficiency,
but one must carefully choose the MOSFET on-resistance
as discussed in the Power MOSFET Selection section.
Power MOSFET Selection
The LTC3709 requires four external N-channel power
MOSFETs, two for the top (main) switches and two for the
bottom (synchronous) switches. Important parameters
for the power MOSFETs are the breakdown voltage
V (BR)DSS , threshold voltage V (GS)TH , on-resistance R DS(ON) ,
reverse transfer capacitance C RSS and maximum current
I DS(MAX) .
The gate drive voltage is set by the 5V DRV CC supply.
Consequently, logic-level threshold MOSFETs must be
used in LTC3709 applications. If the driver’s voltage is
expected to drop below 5V, then sub-logic level threshold
MOSFETs should be used.
When the bottom MOSFETs are used as the current sense
elements, particular attention must be paid to their on-
resistance. MOSFET on-resistance is typically specified
with a maximum value R DS(ON)(MAX) at 25 ° C. In this case
additional margin is required to accommodate the rise in
MOSFET on-resistance with temperature:
JUNCTION TEMPERATURE ( ° C)
3709 F01
Figure 1. R DS(ON) vs Temperature
The ρ T term is a normalization factor (unity at 25 ° C)
accounting for the significant variation in on-resistance
with temperature, typically about 0.4%/ ° C. Junction-to-
case temperature is about 20 ° C in most applications. For
a maximum junction temperature of 100 ° C, using a value
ρ 100 ° C = 1.3 is reasonable (Figure 1).
The power dissipated by the top and bottom MOSFETs
strongly depends upon their respective duty cycles and
the load current. When the LTC3709 is operating in
continuous mode, the duty cycles for the MOSFETs are:
V OUT
V IN
V – V
D BOT
V IN
The maximum power dissipation in the MOSFETs per
channel is:
2
P TOP = D TOP ? ? ? ? ρ T ( TOP ) ? R DS ( ON )( MAX ) +
2
2 ? I ?
? 2 ?
1 1
– V
? I OUT ( MAX ) ?
? ?
R DS ( ON )( MAX ) =
R SENSE
ρ T
2
2
P BOT = D BOT ? ? ? ? ρ T ( BOT ) ? R DS ( ON )( MAX )
3709fb
12
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC-3710 | 制造商:LITEON 制造商全称:Lite-On Technology Corporation 功能描述:0.3 FOUR LED CLOCK FREQUENCY DISPLAYS |
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| LTC-3710G | 功能描述:LED 显示器和配件 4 Digit, Green RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
| LTC-3710HR | 功能描述:LED 显示器和配件 4 Digit, Red RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
| LTC-3710P | 功能描述:LED 显示器和配件 4 Digit, Red RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
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