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| 型号： | LTC3879EUD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 18/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-QFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 2MHz |
| 占空比： | 90% |
| 电源电压： | 4 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 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3879
APPLICATIONS INFORMATION
So, which mode should be programmed? While either
mode in Figure 8 satis?es most practical applications,
the coincident mode offers better output regulation.
This can be better understood with the help of Figure 9.
At the input stage of the LTC3879’s error ampli?er, two
common anode diodes are used to clamp the equivalent
reference voltage and an additional diode is used to match
the shifted common mode voltage. The top two current
sources are of the same ampli?er. In the coincident mode,
the TRACK/SS voltage is substantially higher than 0.6V
at steady-state and effectively turns off D1. D2 and D3
will, therefore, conduct the same current, and offer tight
matching between V FB and the internal precision 0.6V
reference. In the ratiometric mode, however, TRACK/SS
equals 0.6V in steady-state. D1 will divert part of the bias
current to make V FB slightly lower than 0.6V.
Although this error is minimized by the exponential I-V
characteristics of the diode, it does impose a ?nite amount
of output voltage deviation. Furthermore, when the master
supply’s output experiences dynamic excursion (under
load transient, for example), the slave channel output will
be affected as well. For better output regulation, use the
coincident tracking mode instead of ratiometric.
INTV CC to 0V with a small internal NMOS switch. When the
INTV CC UVLO condition is removed, TRACK/SS is released,
beginning a normal soft-start. This feature is important
when regulator start-up is not initiated by applying a logic
drive to RUN.
Ef?ciency Considerations
The percent ef?ciency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the ef?ciency and which change would
produce the most improvement. Although all dissipative
elements in the circuit produce losses, four main sources
account for most of the losses in LTC3879 circuits.
1. DC I 2 R losses. These arise from the resistances of the
MOSFETs, inductor and PC board traces and cause the
ef?ciency to drop at high output currents. In continuous
mode the average output current ?ows though the inductor
L, but is chopped between the top and bottom MOSFETs.
If the two MOSFETs have approximately the same R DS(ON) ,
then the resistance of one MOSFET can simply by summed
with the resistances of L and the board traces to obtain
the DC I 2 R loss. For example, if R DS(ON) = 0.01Ω and
R L = 0.005Ω, the loss will range from 15mW to 1.5W as
the output current varies from 1A to 10A.
I
I
TRACK/SS
0.6V
V FB
D1
D2
3879 F09
D3
+
–
EA
2. Transition loss. This loss arises from the brief amount
of time the top MOSFET spends in the saturated region
during switch node transitions. It depends upon the
input voltage, load current, driver strength and MOSFET
capacitance, among other factors. The loss is signi?cant
at input voltages above 20V.
Figure 9. Equivalent Input Circuit of Error Ampli?er
INTV CC Undervoltage Lockout
Whenever INTV CC drops below approximately 3.4V, the
device enters undervoltage lockout (UVLO). In a UVLO
condition, the switching outputs TG and BG are disabled.
At the same time, the TRACK/SS pin is pulled down from
3. INTV CC current. This is the sum of the MOSFET driver
and control currents.
4. C IN loss. The input capacitor has the dif?cult job of ?lter-
ing the large RMS input current to the regulator. It must have
a very low ESR to minimize the AC I 2 R loss and suf?cient
capacitance to prevent the RMS current from causing ad-
ditional upstream losses in fuses or batteries.
3879f
18
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| LTC3879IMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 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) |
| LTC3879IMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 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) |
| LTC3879IUD#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 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) |
| LTC3879IUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 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) |
| LTC3880EUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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