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參數(shù)資料
| 型號： | LTC3809EMS |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 825 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | PLASTIC, MSOP-10 |
| 文件頁數(shù)： | 11/24頁 |
| 文件大?。?/td> | 266K |
| 代理商： | LTC3809EMS |
19
LTC3809
3809f
Minimum On-Time Considerations
Minimum on-time, tON(MIN) is the smallest amount of time
that the LTC3809 is capable of turning the top P-channel
MOSFET on. It is determined by internal timing delays and
the gate charge required to turn on the top MOSFET. Low
duty cycle and high frequency applications may approach
the minimum on-time limit and care should be taken to
ensure that:
t
V
fV
ON MIN
OUT
OSC
IN
()
<
If the duty cycle falls below what can be accommodated by
the minimum on-time, the LTC3809 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 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 circuits: 1) LTC3809 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.
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) multi-
plied by duty cycle can be summed with the resistance 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
APPLICATIO S I FOR ATIO
WU
UU
Figure 9. Line Regulation of VREF and Maximum Sense Voltage
INPUT VOLTAGE (V)
75
NORMALIZED
VOLTAGE
OR
CURRENT
(%)
85
95
105
80
90
100
2.2
2.4
2.6
2.8
3809 F09
3.0
2.1
2.0
2.3
2.5
2.7
2.9
VREF
MAXIMUM
SENSE VOLTAGE
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參數(shù)描述 |
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| LTC3809EMSE | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3809EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3809EMSE#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3809EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3809EMSE-1 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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