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| 型号： | LTC3809EMS-1 |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 11/24页 |
| 文件大小： | 318K |
| 代理商： | LTC3809EMS-1 |
38091f
LTC3809-1
19
If the duty cycle falls below what can be accommodated by
the minimum on-time, the LTC3809-1 will begin to skip
cycles (unless forced continuous mode is selected). The
output voltage will continue to be regulated, but the ripple
current and ripple voltage will increase. The minimum on-
time for the LTC3809-1 is typically about 210ns. However,
as the peak sense voltage (IL(PEAK) RDS(ON)) decreases,
the minimum on-time gradually increases up to about
260ns. This is of particular concern in forced continuous
applications with low ripple current at light loads. If forced
continuous mode is selected and the duty cycle falls below
the minimum on time requirement, the output will be
regulated by overvoltage protection.
Efficiency Considerations
The efficiency 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 efficiency and which change would produce the
most improvement. Efficiency can be expressed as:
Efficiency = 100% – (L1 + L2 + L3 + …)
where L1, L2, etc. are the individual losses as a percentage
of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3809-1 circuits: 1) LTC3809-1 DC bias
current, 2) MOSFET gate charge current, 3) I2R losses
and 4) transition losses.
1) The VIN (pin) current is the DC supply current, given in
the Electrical Characteristics, which excludes MOSFET
driver currents. VIN current results in a small loss that
increases with VIN.
2) MOSFET gate charge current results from switching the
gate capacitance of the power MOSFET. Each time a
MOSFET gate is switched from low to high to low again, a
packet of charge dQ moves from VIN to ground. The
resulting dQ/dt is a current out of VIN, which is typically
much larger than the DC supply current. In continuous
mode, IGATECHG = f QP.
APPLICATIO S I FOR ATIO
WU
UU
3) I2R losses are calculated from the DC resistances of the
MOSFETs, inductor and/or sense resistor. In continuous
mode, the average output current flows through L but is
“chopped” between the top P-channel MOSFET and the
bottom N-channel MOSFET. The MOSFET RDS(ON)
multiplied by duty cycle can be summed with the resis-
tance of L to obtain I2R losses.
4) Transition losses apply to the external MOSFET and
increase with higher operating frequencies and input
voltages. Transition losses can be estimated from:
Transition Loss = 2 VIN2 IO(MAX) CRSS f
Other losses, including CIN and COUT ESR dissipative
losses and inductor core losses, generally account for less
than 2% total additional loss.
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to (
ILOAD)(ESR),whereESRistheeffectiveseries
resistance of COUT. ILOAD also begins to charge or
discharge COUT generating a feedback error signal used by
the regulator to return VOUT to its steady-state value.
During this recovery time, VOUT can be monitored for
overshoot or ringing that would indicate a stability prob-
lem. OPTI-LOOP compensation allows the transient re-
sponse to be optimized over a wide range of output
capacitance and ESR values.
The ITH series RC-CC filter (see Functional Diagram) sets
the dominant pole-zero loop compensation.
The ITH external components showed in the figure on the
first page of this data sheet will provide adequate compen-
sation for most applications. The values can be modified
slightly (from 0.2 to 5 times their suggested values) to
optimize transient response once the final PC layout is
done and the particular output capacitor type and value
have been determined. The output capacitor needs to be
decided upon because the various types and values deter-
mine the loop feedback factor gain and phase. An output
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相关代理商/技术参数 |
参数描述 |
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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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