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参数资料
| 型号： | LTC4088EDE-1#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO14 |
| 封装： | 4 X 3 MM, 0.75 MM HEIGHT, PLASTIC, MO-229WGED-3, DFN-14 |
| 文件页数： | 8/24页 |
| 文件大小： | 906K |
| 代理商： | LTC4088EDE-1#TR |
LTC4088-1
40881fa
APPLICATIO S I FOR ATIO
W
U
CLPROG Resistor and Capacitor
As described in the Step-Down Input Regulator section,
the resistor on the CLPROG pin determines the average
input current limit in each of the six current limit modes.
The input current will be comprised of two components,
the current that is used to drive VOUT and the quiescent
current of the switching regulator. To ensure that the USB
specification is strictly met, both components of input cur-
rent should be considered. The Electrical Characteristics
table gives the typical values for quiescent currents in all
settings as well as current limit programming accuracy.
To get as close to the 500mA or 100mA specifications as
possible, a precision resistor should be used.
An averaging capacitor is required in parallel with the
resistor so that the switching regulator can determine
the average input current. This capacitor also provides
the dominant pole for the feedback loop when current
limit is reached. To ensure stability, the capacitor on
CLPROG should be 0.47F or larger. Alternatively, faster
transient response may be obtained with 0.1F in series
with 8.2
Ω.
Choosing the Inductor
Becausetheaverageinputcurrentcircuitdoesnotmeasure
reverse current (i.e., current from VOUT to VBUS), cur-
rent reversal in the inductor at light loads will contribute
an error to the VBUS current measurement. The error is
conservative in that if the current reverses, the voltage
at CLPROG will be higher than what would represent the
actual average input current drawn. The current available
for charging and the system load is thus reduced. The
USB specification will not be violated.
This reduction in available VBUS current will happen when
the peak-peak inductor ripple is greater than twice the
average current limit setting. For example, if the average
current limit is set to 100mA, the peak-peak ripple should
not exceed 200mA. If the input current is less than 100mA,
the measurement accuracy may be reduced, but it does
not affect the average current loop since it will not be in
regulation.
The LTC4088-1 includes a current-reversal compara-
tor which monitors inductor current and disables the
synchronous rectifier as current approaches zero. This
comparator will minimize the effect of current reversal
on the average input current measurement. For some
low inductance values, however, the inductor current
may reverse slightly. This value depends on the speed
of the comparator in relation to the slope of the cur-
rent waveform, given by VL/L, where VL is the voltage
across the inductor (approximately –VOUT) and L is the
inductance value.
An inductance value of 3.3H is a good starting value. The
ripple will be small enough for the regulator to remain in
continuousconductionat100mAaverageVBUScurrent.At
lighter loads the current-reversal comparator will disable
thesynchronousrectifieratacurrentslightlyabove0mA.As
theinductanceisreducedfromthisvalue,thepartwillenter
discontinuous conduction mode at progressively higher
loads. Ripple at VOUT will increase, directly proportionally
to the magnitude of inductor ripple. Transient response,
however, will be improved. The current mode controller
controls inductor current to exactly the amount required
by the load to keep VOUT in regulation. A transient load
step requires the inductor current to change to a new level.
Sinceinductorcurrentcannotchangeinstantaneously,the
capacitance on VOUT delivers or absorbs the difference in
current until the inductor current can change to meet the
new load demand. A smaller inductor changes its current
morequicklyforagivenvoltagedrivethanalargerinductor,
resultinginfastertransientresponse.Alargerinductorwill
reduce output ripple and current ripple, but at the expense
ofreducedtransientperformance(ormoreCVOUTrequired)
and a physically larger inductor package size.
The input regulator has an instantaneous peak current
clamp to prevent the inductor from saturating during tran-
sient load or start-up conditions. The clamp is designed
so that it does not interfere with normal operation at
highloadswithreasonableinductorripple.Itwillprevent
inductor current runaway in case of a shorted output.
The DC winding resistance and AC core losses of the
inductor will affect efficiency, and therefore available
output power. These effects are difficult to characterize
and vary by application. Some inductors which may be
suitable for this application are listed in Table 3.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4088EDE-1-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Effi ciency Battery Charger/USB Power Manager with Regulated Output Voltage |
| LTC4088EDE-2#PBF | 功能描述:IC CHRGR BATT HE 14-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电池管理 系列:- 标准包装:61 系列:- 功能:电源管理 电池化学:锂离子（Li-Ion）、锂聚合物（Li-Pol） 电源电压:4.35 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:22-WFDFN 裸露焊盘 供应商设备封装:22-DFN（6x3）裸露焊盘 包装:管件 |
| LTC4088EDE-2#TRPBF | 功能描述:IC CHRGR BATT HE 14-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电池管理 系列:- 标准包装:61 系列:- 功能:电源管理 电池化学:锂离子（Li-Ion）、锂聚合物（Li-Pol） 电源电压:4.35 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:22-WFDFN 裸露焊盘 供应商设备封装:22-DFN（6x3）裸露焊盘 包装:管件 |
| LTC4088EDE-2-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Effi ciency Battery Charger/USB Power Manager with Regulated Output Voltage |
| LTC4088EDE-2-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Effi ciency Battery Charger/USB Power Manager with Regulated Output Voltage |
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