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參數(shù)資料
| 型號(hào)： | LTC3445EUF#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 1800 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封裝： | 4 X 4 MM, LEAD FREE, PLASTIC, MO-220-WGGD, QFN-24 |
| 文件頁數(shù)： | 11/24頁 |
| 文件大?。?/td> | 470K |
| 代理商： | LTC3445EUF#TRPBF |
19
LTC3445
3445fa
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), where ESR is the effective series
resistance of COUT. ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steady-
state value. During this recovery time VOUT can be moni-
tored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
A second, more severe transient is caused by switching in
loads with large (>1
F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25 CLOAD).
Thus, a 10
F capacitor charging to 3.3V would require a
250
s rise time, limiting the charging current to about
130mA.
LDO REGULATORS
The LDOs in the LTC3445 are 50mA low dropout regula-
tors with low quiescent and shutdown currents. Each
device is capable of supplying 50mA at a dropout voltage
of 300mV. The LDOs are current limited to greater than
50mA but less than 75mA. The output voltages of the
LDOs are set with external resistive dividers according to
the following formula:
VLDOOUT1 = 0.6(1 + R1/R2)
(4)
VLDOOUT2 = 0.6(1 + R3/R4)
(5)
Output Capacitance and Transient Response
The LTC3445 LDOs are designed to be stable with a wide
range of output capacitors. A minimum output capacitor
of 2.2
F with an ESR of 3 or less is recommended to
internal power MOSFET switches. Each time the gate is
switched from high to low to high again, a packet of
charge, dQ, moves from VCC1 to ground. The resulting
dQ/dt is the current out of VCC1 that is typically larger
than the DC bias current. In continuous mode, IGATECHG
= f(QT + QB) where QT and QB are the gate charges of the
internal top and bottom switches. Both the DC bias and
gate charge losses are proportional to VCC1 and thus
their effects will be more pronounced at higher supply
voltages.
2. I2R losses are calculated from the resistances of the
internal switches, RSW, and external inductor RL. In
continuous mode, the average output current flowing
through inductor L is “chopped” between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
top and bottom MOSFET RDS(ON) and the duty cycle
(DC) as follows:
RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs can
be obtained from the Typical Performance Charateristics
curves. Thus, to obtain I2R losses, simply add RSW to
RL and multiply the result by the square of the average
output current.
Other losses including CIN and COUT ESR dissipative
losses and inductor core losses generally account for
less than 2% total additional loss.
APPLICATIO S I FOR ATIO
WU
UU
Figure 8. Power Loss vs Load Current, VCC1 = 3.6V
LOAD CURRENT (mA)
1
POWER
LOSS
(mW)
10
100
1000
0.1
10
100
1000
3445 F08
0.1
1
DAC MIN
DAC MAX
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| LTC3446 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic Buck Regulator with Dual VLDO Regulators |
| LTC3446EDE | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic Buck Regulator with Dual VLDO Regulators |
| LTC3446EDE#PBF | 功能描述:IC REG TRPL BCK/LINEAR 14-DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 + 切換式 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 拓?fù)?降壓（降壓）同步（3），線性（LDO）（2） 功能:任何功能 輸出數(shù):5 頻率 - 開關(guān):300kHz 電壓/電流 - 輸出 1:控制器 電壓/電流 - 輸出 2:控制器 電壓/電流 - 輸出 3:控制器 帶 LED 驅(qū)動(dòng)器:無 帶監(jiān)控器:無 帶序列發(fā)生器:是 電源電壓:5.6 V ~ 24 V 工作溫度:-40°C ~ 85°C 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* |
| LTC3446EDE#TRPBF | 功能描述:IC REG TRPL BCK/LINEAR 14-DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 + 切換式 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 拓?fù)?降壓（降壓）同步（3），線性（LDO）（2） 功能:任何功能 輸出數(shù):5 頻率 - 開關(guān):300kHz 電壓/電流 - 輸出 1:控制器 電壓/電流 - 輸出 2:控制器 電壓/電流 - 輸出 3:控制器 帶 LED 驅(qū)動(dòng)器:無 帶監(jiān)控器:無 帶序列發(fā)生器:是 電源電壓:5.6 V ~ 24 V 工作溫度:-40°C ~ 85°C 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* |
| LTC3446EDE-PBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic Buck Regulator with Dual VLDO Regulators |
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