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参数资料
| 型号： | LTC3109EGN#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 0.026 A SWITCHING REGULATOR, PDSO20 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-20 |
| 文件页数： | 9/24页 |
| 文件大小： | 329K |
| 代理商： | LTC3109EGN#PBF |
LTC3109
3109f
applicaTions inForMaTion
DESIGN EXAMPLE 1
This design example will explain how to calculate the
necessary reservoir capacitor value for VOUT in pulsed-
load applications, such as a wireless sensor/transmitter.
In these types of applications, the load is very small for a
majority of the time (while the circuitry is in a low power
sleep state), with pulses of load current occurring periodi-
cally during a transmit burst.
The reservoir capacitor on VOUT supports the load during
the transmit pulse; the long sleep time between pulses
allows the LTC3109 to accumulate energy and recharge
the capacitor (either from the input voltage source or the
storage capacitor). A method for calculating the maximum
rate at which the load pulses can occur for a given output
current from the LTC3109 will also be shown.
In this example, VOUT is set to 3.3V, and the maximum
allowed voltage droop during a transmit pulse is 10%, or
0.33V. The duration of a transmit pulse is 5ms, with a total
average current requirement of 20mA during the pulse.
Given these factors, the minimum required capacitance
on VOUT is:
C
F
mA ms
V
F
OUT (
)≥
=
20
5
0 33
303
.
Note that this equation neglects the effect of capacitor ESR
on output voltage droop. For ceramic capacitors and low
ESR tantalum capacitors, the ESR will have a negligible
effectattheseloadcurrents.However,bewareofthevoltage
coefficient of ceramic capacitors, especially those in small
case sizes. This greatly reduces the effective capacitance
when a DC bias is applied.
A standard value of 330F could be used for COUT in
this case. Note that the load current is the total current
draw on VOUT, VOUT2 and VLDO, since the current for all
of these outputs must come from VOUT during a pulse.
Current contribution from the capacitor on VSTORE is not
considered, since it may not be able to recharge between
pulses. Also, it is assumed that the harvested charge
current from the LTC3109 is negligible compared to the
magnitude of the load current during the pulse.
To calculate the maximum rate at which load pulses can
occur, you must know how much charge current is avail-
able from the LTC3109 VOUT pin given the input voltage
source being used. This number is best found empirically,
since there are many factors affecting the efficiency of the
converter. You must also know what the total load cur-
rent is on VOUT during the sleep state (between pulses).
Note that this must include any losses, such as storage
capacitor leakage.
Let’s assume that the charge current available from the
LTC3109 is 150A and the total current draw on VOUT and
VLDOinthesleepstateis17A,includingcapacitorleakage.
We’ll also use the value of 330F for the VOUT capacitor.
The maximum transmit rate (neglecting the duration of
the transmit pulse, which is very short compared to the
period) is then given by:
T
F
V
A
or f
Hz
MAX
=
330
0 33
150
17
0 82
1 2
.
–
. sec
.
Therefore, in this application example, the circuit can sup-
port a 5ms transmit pulse of 20mA every 0.82 seconds.
It can be seen that for systems that only need to transmit
every few seconds (or minutes or hours), the average
charge current required is extremely small, as long as
the sleep or standby current is low. Even if the available
charge current in the example above was only 21A, if the
sleep current was only 5A, it could still transmit a pulse
every seven seconds.
The following formula will allow you to calculate the time
it will take to charge the LDO output capacitor and the
VOUT capacitor the first time, from zero volts. Here again,
the charge current available from the LTC3109 must be
known. For this calculation, it is assumed that the LDO
output capacitor is 2.2F:
t
V
F
I
LDO
CHG
LDO
=
2 2 2 2
.
.
–
If there was 150A of charge current available and a 5A
load on the LDO (when the processor is sleeping), the time
for the LDO to reach regulation would be only 33ms.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3109EGN-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Auto-Polarity, Ultralow Voltage Step-Up Converter and Power Manager |
| LTC3109EUF#PBF | 功能描述:IC BOOST CONVERTER PMU 20QFN 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 |
| LTC3109EUF#TRPBF | 功能描述:IC BOOST CONVERTER PMU 20QFN 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 |
| LTC3109EUF-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Auto-Polarity, Ultralow Voltage Step-Up Converter and Power Manager |
| LTC3109EUF-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Auto-Polarity, Ultralow Voltage Step-Up Converter and Power Manager |
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