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參數(shù)資料
| 型號(hào)： | LTC1772BES6 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Constant Frequency Current Mode Step-Down DC/DC Controller in SOT-23 |
| 中文描述： | 1 A SWITCHING CONTROLLER, 650 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封裝： | PLASTIC, MO-193, SOT-23, 6 PIN |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 196K |
| 代理商： | LTC1772BES6 |
9
LTC1772B
Setting Output Voltage
The regulated output voltage is determined by:
V
R
R
OUT
=
+
0.
2
1
For most applications, an 80k resistor is suggested for R1.
To prevent stray pickup, locate resistors R1 and R2 close
to LTC1772B.
APPLICATIO
S I
N
FOR
ATIO
U
W
U
1. The V
IN
current is the DC supply current, given in the
electrical characteristics, that excludes MOSFET driver
and control currents. V
IN
current results in a small loss
which increases with V
IN
.
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 V
IN
to ground.
The resulting dQ/dt is a current out of V
IN
which is
typically much larger than the DC supply current. In
continuous mode, I
GATECHG
= f(Qp).
3. I
2
R losses are predicted from the DC resistances of the
MOSFET, inductor and current shunt. In continuous
mode the average output current flows through L but
is “chopped” between the P-channel MOSFET (in se-
ries with R
SENSE)
and the output diode. The MOSFET
R
DS(ON)
plus R
SENSE
multiplied by duty cycle can be
summed with the resistances of L and R
SENSE
to obtain
I
2
R losses.
4. The output diode is a major source of power loss at
high currents and gets worse at high input voltages.
The diode loss is calculated by multiplying the forward
voltage times the diode duty cycle multiplied by the
load current. For example, assuming a duty cycle of
50% with a Schottky diode forward voltage drop of
0.4V, the loss increases from 0.5% to 8% as the load
current increases from 0.5A to 2A.
5. Transition losses apply to the external MOSFET and
increase at higher operating frequencies and input
voltages. Transition losses can be estimated from:
Transition Loss = 2(V
IN
)
2
I
O(MAX)
C
RSS
(f)
Other losses including C
IN
and C
OUT
ESR dissipative
losses, and inductor core losses, generally account for
less than 2% total additional loss.
Figure 5. Setting Output Voltage
3
V
FB
V
OUT
LTC1772B
R1
1772 F04
R2
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 the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
Efficiency = 100% – (
η
1 +
η
2 +
η
3 + ...)
where
η
1,
η
2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC1772B circuits: 1) LTC1772B DC bias cur-
rent, 2) MOSFET gate charge current, 3) I
2
R losses and 4)
voltage drop of the output diode.
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| LTC1772BES6#TRM | 功能描述:IC REG CTRLR BUCK PWM CM SOT23-6 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) |
| LTC1772BES6#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM CM SOT23-6 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
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