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参数资料
| 型号： | LTC3786EMSE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 14/34页 |
| 文件大小： | 397K |
| 代理商： | LTC3786EMSE#TRPBF |
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LTC3786
21
3786fa
applicaTions inForMaTion
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 load current.
When a load step occurs, VOUT shifts by an amount equal
to
ILOAD(ESR),whereESRistheeffectiveseriesresistance
of COUT. ILOAD also begins to charge or discharge COUT
generatingthefeedbackerrorsignalthatforcestheregula-
tor 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. OPTI-LOOP compen-
sation allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
availability of the ITH pin not only allows optimization of
control loop behavior, but it also provides a DC-coupled
and AC-filtered closed-loop response test point. The DC
step,risetimeandsettlingatthistestpointtrulyreflectsthe
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.Thebandwidthcanalsobeestimatedbyexaminingthe
rise time at the pin. The ITH external components shown
in the Figure 8 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
to optimize transient response once the final PCB layout
is complete and the particular output capacitor type and
value have been determined. The output capacitors must
beselectedbecausethevarioustypesandvaluesdetermine
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 and load resistor directly
across the output capacitor and driving the gate with an
appropriate pulse generator is a practical way to produce
a realistic load step condition. The initial output voltage
step resulting from the step change in output current
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 compensated
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-loopsystemandwilldemonstratetheactualoverall
supply performance.
A second, more severe transient is caused by switching
in loads with large (>1F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
alter its delivery of current quickly enough to prevent this
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
CLOAD to COUT is greater than 1:50, the switch rise time
should be controlled so that the load rise time is limited to
approximately 25 CLOAD. Thus, a 10F capacitor would
require a 250s rise time, limiting the charging current
to about 200mA.
Design Example
As a design example, assume VIN = 12V(nominal),
VIN=22V(max),VOUT=24V,IOUT(MAX)=4A,VSENSE(MAX)
= 75mV and f = 350kHz.
The inductance value is chosen first based on a 30% ripple
current assumption. Tie the MODE/PLLIN pin to GND,
generating 350kHz operation. The minimum inductance
for 30% ripple current is:
IL =
VIN
f L
1– VIN
VOUT
The largest ripple happens when VIN = 1/2VOUT = 12V,
where the average maximum inductor is IMAX = IOUT(MAX)
(VOUT/VIN) = 8A. A 6.8H inductor will produce a 31%
ripple current. The peak inductor current will be the maxi-
mum DC value plus one-half the ripple current, or 9.25A.
相关PDF资料 |
PDF描述 |
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| LTC3786EMSE#PBF | SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PDSO16 |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3786EUD#PBF | 功能描述:IC REG CTRLR BST PWM CM 16-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3786EUD#PBF | 制造商:Linear Technology 功能描述:IC, DC-DC CONV, 550kHz, QFN16 |
| LTC3786EUD#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 16-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3786IMSE#PBF | 功能描述:IC REG CTRLR BST PWM CM 16-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3786IMSE#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 16-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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