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參數(shù)資料
| 型號： | LTC3773EUHF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PQCC38 |
| 封裝： | 5 X 7 MM, PLASTIC, MO-220WHKD, QFN-38 |
| 文件頁數(shù)： | 17/32頁 |
| 文件大小： | 461K |
| 代理商： | LTC3773EUHF |
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LTC3773
24
3773fa
DIGITAL
PHASE/
FREQUENCY
DETECTOR
VCC
RPLLFL2
CLP
3773 F07
PLLFLTR
RPLLFL1
PHASE
DETECTOR/
OSCILLATOR
PLLIN/FC
BG1
CLKOUT
OSCILLATOR
Figure 7. Fixed Frequency Adjustment
The LTC3773 can be congured to operate at any switch-
ing frequency within the synchronization range. Figure 7
shows a simple circuit to achieve this. The resistive divider
at the PLLFLTR pin programs the LTC3773 switching
frequency according to the transfer curve of Figure 6b. By
connecting the PLLIN/FC pin to the BG1 or the CLKOUT
(UHF package only) node, the pre-set frequency selection
is disengaged and the PLLFLTR pin potential determines
the switching frequency.
ripple current at light loads. If the duty cycle drops below
the minimum on-time limit in this situation, a signicant
amount of cycle skipping can occur with correspondingly
larger current and voltage ripple.
If an application can operate close to the minimum on-time
limit, an inductor must be chosen that is low enough in
value to provide sufcient ripple amplitude to meet the
minimum on-time requirement. As a general rule, keep
the inductor ripple current for each channel equal to or
greater than 30% of IOUT(MAX) at VIN(MAX).
Efciency Considerations
The percent efciency 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 efciency and which change would
produce the most improvement. Percent efciency can
be expressed as:
%Efciency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Checking Transient Response
The regulator loop response can be checked by look-
ing at the load transient response. Switching regulators
take several cycles to respond to a step in DC (resistive)
load current. When a load step occurs, VOUT shifts by an
amount equal to
ΔILOAD ESR, where ESR is the effective
series resistance of COUT. ΔILOAD also begins to charge or
discharge COUT, generating the feedback error signal that
forces the regulator to adapt to the current change and
return VOUT to its steady-state value. During this recovery
time, VOUT can be monitored for excessive overshoot or
ringing, which would indicate a stability problem. The
availability of the ITH pin not only allows optimization of
control loop behavior, but also provides a DC coupled and
AC ltered closed-loop response test point. The DC step,
rise time and settling at this test point truly reects the
closed-loop response. Assuming a predominantly second
order system, phase margin and/or damping factor can be
estimated using the percentage of overshoot seen at this
pin. The bandwidth can also be estimated by examining
the rise time at the pin.
Minimum On-Time Considerations
Minimum on-time, tON(MIN), is the smallest time duration
that the IC is capable of turning on the top MOSFET. It is
determined by internal timing delays and the gate charge
of the top MOSFET. Low duty cycle applications may
approach this minimum on-time limit and care should be
taken to ensure that:
t
V
Vf
ON MIN
OUT
IN
()
<
If the duty cycle falls below what can be accommodated
by the minimum on-time, the IC will begin to skip every
other cycle, resulting in half-frequency operation. The
output voltage will continue to be regulated, but the ripple
current and ripple voltage will increase.
The minimum on-time for the IC is generally about
130ns. However, as the peak sense voltage decreases,
the minimum on-time gradually increases. This is of par-
ticular concern in forced continuous applications with low
APPLICATIONS INFORMATION
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| LTC3773EUHF#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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 |
| LTC3773EUHF#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 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:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC3774EUHE#PBF | 制造商:Linear Technology 功能描述:SWITCHING REG, BUCK, ADJ, 2.2MHZ, DFN-36 |
| LTC3774IUHE#PBF | 制造商:Linear Technology 功能描述:SWITCHING REG, BUCK, ADJ, 2.2MHZ, DFN-36 |
| LTC3775EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-MSOP 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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