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參數(shù)資料
| 型號(hào)： | LTC3856EFE#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO38 |
| 封裝： | 4.4 MM, LEAD FREE, PLASTIC, TSSOP-38 |
| 文件頁數(shù)： | 26/40頁 |
| 文件大?。?/td> | 2222K |
| 代理商： | LTC3856EFE#TRPBF |
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LTC3856
3856f
the topside MOSFET and the synchronous MOSFET. If
thetwoMOSFETshaveapproximatelythesameRDS(ON),
then the resistance of one MOSFET can simply be
summed with the resistances of L and RSENSE to ob-
tain I2R losses. For example, if each RDS(ON) = 10mΩ,
RL = 10mΩ, RSENSE = 5mΩ, then the total resistance is
25mΩ. This results in losses ranging from 2% to 8%
as the output current increases from 3A to 15A for a 5V
output, or a 3% to 12% loss for a 3.3V output.
Efficiency varies as the inverse square of VOUT for the
same external components and output power level. The
combined effects of increasingly lower output voltages
andhighercurrentsrequiredbyhighperformancedigital
systemsisnotdoublingbutquadruplingtheimportance
of loss terms in the switching regulator system!
4. Transition losses apply only to the topside MOSFET(s),
and become significant only when operating at high
input voltages (typically 15V or greater). Transition
losses can be estimated from:
Transition Loss = (1.7) VIN2 IO(MAX) CRSS f
Other hidden losses such as copper trace and internal
battery resistances can account for an additional 5%
to 10% efficiency degradation in portable systems. It
is very important to include these system level losses
during the design phase. The internal battery and fuse
resistance losses can be minimized by ensuring that
CIN has adequate charge storage and very low ESR at
the switching frequency. A 25W supply will typically
require a minimum of 20F to 40F of capacitance
having a maximum of 20mΩ to 50mΩ of ESR. Other
losses including Schottky conduction losses during
dead time 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 current 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
ILOAD (ESR), where ESR is the effective
series resistance of COUT. ILOAD 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-filtered closed-loop response test point. The DC step,
rise time and settling at this test point truly reflects 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.
TheITHexternalcomponentsshownintheTypicalApplica-
tion circuit will provide an adequate starting point for most
applications. The ITH series RC-CC filter sets the dominant
pole-zero loop compensation. The values can be modified
slightly (from 0.5 to 2 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 capacitors need to be
selected because the various types and values determine
the loop gain and phase. An output current pulse of 20%
to 80% of full-load current having a rise time of 1s to
10s will produce output voltage and ITH pin waveforms
that will give a sense of the overall loop stability without
breaking the feedback loop. Placing a power MOSFET
directly across the output capacitor and driving the gate
with an appropriate signal generator is a practical way to
produce a realistic load step condition. The initial output
voltage step resulting from the step change in output cur-
rent may not be within the bandwidth of the feedback loop,
so this signal cannot be used to determine phase margin.
This is why it is better to look at the ITH pin signal which
is in the feedback loop and is the filtered and compen-
sated control loop response. The gain of the loop will be
increased by increasing RC and the bandwidth of the loop
will be increased by decreasing CC. If RC is increased by
the same factor that CC is decreased, the zero frequency
will be kept the same, thereby keeping the phase shift the
same in the most critical frequency range of the feedback
loop. The output voltage settling behavior is related to the
stability of the closed-loop system and will demonstrate
the actual overall supply performance.
applicaTions inForMaTion
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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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| LTC3856EUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32WFQFN 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: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) |
| LTC3856EUH#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: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) |
| LTC3856IFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TFSOP 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 |
| LTC3856IFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TSSOP 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 |
| LTC3856IUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32WFQFN 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: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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