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| 型号： | LTC3809EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-DFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 825kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 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： | 10-WFDFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
LTC3809
APPLICATIONS INFORMATION
The typical LTC3809 application circuit is shown in Fig-
ure 10. External component selection for the controller
is driven by the load requirement and begins with the
selection of the inductor and the power MOSFETs.
where I RIPPLE is the inductor peak-to-peak ripple current
(see Inductor Value Calculation).
A reasonable starting point is setting ripple current I RIPPLE
to be 40% of I OUT(MAX) . Rearranging the above equation
Power MOSFET Selection
The LTC3809’s controller requires two external power
MOSFETs: a P-channel MOSFET for the topside (main)
yields:
R DS ( ON ) MAX =
5 Δ V SENSE(MAX )
?
6 I OUT ( MAX )
for Duty Cycle < 20 %
R DS ( ON ) MAX =
switchandaN-channelMOSFETforthebottom(synchro-
nous) switch. The main selection criteria 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 , turn-off delay t D(OFF) and the total gate
charge Q G .
The gate drive voltage is the input supply voltage. Since
the LTC3809 is designed for operation down to low input
voltages, a sublogic level MOSFET (R DS(ON) guaranteed at
V GS = 2.5V) is required for applications that work close to
this voltage. When these MOSFETs are used, make sure that
the input supply to the LTC3809 is less than the absolute
maximum MOSFET V GS rating, which is typically 8V.
The P-channel MOSFET’s on-resistance is chosen based
on the required load current. The maximum average load
current I OUT(MAX) is equal to the peak inductor current
However, for operation above 20% duty cycle, slope
compensation has to be taken into consideration to select
the appropriate value of R DS(ON) to provide the required
amount of load current:
5 Δ V SENSE(MAX )
? SF ?
6 I OUT ( MAX )
where SF is a scale factor whose value is obtained from
the curve in Figure 1.
These must be further derated to take into account the
signi?cant variation in on-resistance with temperature.
The following equation is a good guide for determining the
required R DS(ON)MAX at 25°C (manufacturer’s speci?ca-
tion), allowing some margin for variations in the LTC3809
and external component values:
minus half the peak-to-peak ripple current I RIPPLE . The
LTC3809’s current comparator monitors the drain-to-
source voltage V DS of the top P-channel MOSFET, which
R DS ( ON ) MAX =
5
6
? 0 . 9 ? SF ?
Δ V SENSE(MAX )
I OUT ( MAX ) ? ρ T
is sensed between the V IN and SW pins. The peak induc-
tor current is limited by the current threshold, set by the
voltage on the I TH pin, of the current comparator. The
voltage on the I TH pin is internally clamped, which limits
the maximum current sense threshold Δ V SENSE(MAX) to
approximately 125mV when IPRG is ?oating (85mV when
IPRG is tied low; 204mV when IPRG is tied high).
The output current that the LTC3809 can provide is given
by:
The ρ T is a normalizing term accounting for the temperature
variation in on-resistance, which is typically about 0.4%/°C,
as shown in Figure 2. Junction-to-case temperature T JC is
about 10°C in most applications. For a maximum ambi-
ent temperature of 70°C, using ρ 80°C ~ 1.3 in the above
equation is a reasonable choice.
The N-channel MOSFET’s on resistance is chosen based
on the short-circuit current limit (I SC ). The LTC3809’s
short-circuit current limit comparator monitors the drain-
– RIPPLE
I OUT ( MAX ) =
Δ V SENSE(MAX )
R DS ( ON )
I
2
to-source voltage V DS of the bottom N-channel MOSFET,
which is sensed between the GND and SW pins. The
3809fc
12
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| LTC3809EMSE | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 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) |
| LTC3809EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-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) |
| LTC3809EMSE#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 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) |
| LTC3809EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-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) |
| LTC3809EMSE-1 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 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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