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参数资料
| 型号： | LTC4425EDD#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO12 |
| 封装： | 3 X 3 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, DFN-12 |
| 文件页数： | 4/20页 |
| 文件大小： | 239K |
| 代理商： | LTC4425EDD#PBF |
LTC4425
12
4425f
Programming the Output Voltage
In LDO mode, the LTC4425 output voltage can be pro-
grammed for any voltage between 2.7V and VIN by using
a resistor divider from VOUT pin to GND via the FB pin
such that:
VOUT = VFB (1 + RFB1/RFB2)
where VFB is 1.2V. See Figure 3.
Typical values for RFB are in the range of 40k to 1M. Too
small a resistor will result in a large quiescent current
whereas too large a resistor coupled with FB pin capaci-
tance will create an additional pole and may cause loop
instability.
APPLICATIONS INFORMATION
PROG pin. The program resistor and the charge current
are calculated using the following equations:
RPROG = 1000 (1V/ICHRG), ICHRG = 1000 (1V/RPROG)
where ICHRG is the charge current out of the VOUT pin. The
charge current out of the VOUT pin can be determined at
any time by monitoring the PROG pin voltage and using
the following equation:
ICHRG = 1000 (VPROG/RPROG)
Stability Considerations
In LDO mode, the LTC4425 supercapacitor charger
has two principal control loops: constant-voltage and
constant-current. The constant-voltage loop is stable
when connected to a supercap of at least 0.2F. However,
when disconnected from the supercap, the voltage loop
requires at least 10μF capacitance in series with 500Ω
resistance for stability.
In constant-current mode, the PROG pin voltage is in
the feedback loop, not the VOUT pin voltage. Because of
the additional pole created by the PROG pin capacitance,
capacitance on this pin must be kept to a minimum. With
no additional capacitance on the PROG pin, the charger is
stable with a program resistor as high as 100k. However,
any additional capacitance on this node reduces the
maximum allowed program resistor. The pole frequency
at the PROG pin should be kept above 100kHz. Therefore,
if the PROG pin is loaded with a capacitance, CPROG,
the following equation should be used to calculate the
maximum resistance value for RPROG:
RPROG ≤ 1/(2π 100kHz CPROG)
Board Layout Considerations
To be able to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on
the backside of the LTC4425’s two packages have a good
thermal contact to the PC board ground. Correctly soldered
to a 2500mm2 double-sided 1 oz. copper board, the DFN
package has a thermal resistance of approximately 43°C/W.
Failure to make thermal contact between the exposed pad
on the backside of the package and the copper board will
result in a thermal resistance far greater than 43°C/W.
4425 F03
LTC4425
PFI
FB
PFI_RET
RPF1
RPF2
RFB1
RFB2
VIN
VOUT
Figure 3. Programming Output Voltage and Input
Threshold for Power Fail Comparator.
Programming the Input Voltage Threshold for Power
Fail Status Indicator
The input voltage below which the power fail status pin
PFO indicates a power-fail condition is programmed by
using a resistor divider from the VIN pin to the PFI_RET
pin via the PFI pin such that:
VIN, PFO = VPFI (1 + RPF1/RPF2)
where VPFI is 1.2V. See Figure 3.
Typical values for RPF are in the range of 40k to 1M. In
shutdown mode, this divider network is disconnected from
ground via the PFI_RET pin to save the quiescent current
drawn by the network.
Programming the Charge Current
The LTC4425 charge current is programmed using a single
resistor from the PROG pin to ground. The charge current
out of the VOUT pin is 1000 times the current out of the
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| LTC4425EMSE#PBF | 功能描述:IC SUPERCAP CHARGER 12-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:50 系列:- 应用:热电冷却器 电流 - 电源:- 电源电压:3 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:28-SOIC（0.173"，4.40mm 宽）裸露焊盘 供应商设备封装:28-TSSOP 裸露焊盘 包装:管件 产品目录页面:1410 (CN2011-ZH PDF) |
| LTC4425EMSE#TRPBF | 功能描述:IC SUPERCAP CHRGR DIO/MON 12MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 标准包装:1 系列:- 应用:手持/移动设备 电流 - 电源:- 电源电压:3 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:14-WFDFN 裸露焊盘 供应商设备封装:14-LLP-EP（4x4） 包装:Digi-Reel® 配用:LP3905SD-30EV-ND - BOARD EVALUATION LP3905SD-30 其它名称:LP3905SD-30DKR |
| LTC4425IDD#PBF | 功能描述:IC SUPERCAP CHARGER 12-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 标准包装:1 系列:- 应用:手持/移动设备 电流 - 电源:- 电源电压:3 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:14-WFDFN 裸露焊盘 供应商设备封装:14-LLP-EP（4x4） 包装:Digi-Reel® 配用:LP3905SD-30EV-ND - BOARD EVALUATION LP3905SD-30 其它名称:LP3905SD-30DKR |
| LTC4425IDD#TRPBF | 功能描述:IC SUPERCAP CHRGR DIO/MON 12DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 标准包装:1 系列:- 应用:手持/移动设备 电流 - 电源:- 电源电压:3 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:14-WFDFN 裸露焊盘 供应商设备封装:14-LLP-EP（4x4） 包装:Digi-Reel® 配用:LP3905SD-30EV-ND - BOARD EVALUATION LP3905SD-30 其它名称:LP3905SD-30DKR |
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