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| 型号： | LTC3125EDCB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/18页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST SYNC ADJ 1.2A 8DFN |
| 标准包装： | 2,500 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 2 V ~ 5.25 V |
| 输入电压： | 1.8 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1.6MHz |
| 电流 - 输出： | 1.2A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-DFN（3x2） |
LTC3125
APPLICATIONS INFORMATION
Burst Mode operation is inhibited during start-up and
soft-start and until V OUT is at least 0.38V greater than V IN .
GSM and GPRS modems have become a popular wire-
less data transfer solution for use in notebook PCs and
other mobile systems. GSM transmission requires large
bursts of current that exceed the maximum peak current
speci?cations for CompactFlash and PCMCIA bus power.
The GSM standard speci?es a 577μs, 2A (typical) trans-
mission burst within a 4.6ms period (12.5% duty cycle).
During the receive and standby periods the current con-
sumption drops to 70mA (typical), yielding an average
current requirement of 320mA.
Other standards (such as GPRS, Class 10) de?ne a higher
data rate. One popular requirement transmits two 2A bursts
(3A worst case) within a 4.6ms frame period (70mA standby
current) demanding an 800mA average input current. The
LTC3125 external current limit programming resistor can
be easily adjusted for this requirement.
Further, the GSM module is typically speci?ed to operate
over an input power range that is outside that allowed in
the PCMCIA or CompactFlash bus power speci?cation.
The LTC3125 is a high ef?ciency boost converter with
programmable input average current limit that provides
the needed ?exibility when designing a GSM/GPRS power
supply solution. The high ef?ciency of the converter maxi-
mizes the average output power without overloading the
bus. A bulk output capacitor is used to supply the energy
and maintain the output voltage during the high current
pulses.
short-circuit conditions; the peak switch current limit is
reduced to 800mA (typical).
SCHOTTKY DIODE
Although it is not necessary, adding a Schottky diode from
SW to V OUT will improve ef?ciency by about 4%. Note that
this defeats the output disconnect, short-circuit protection
and average input limiting during start-up.
PCB LAYOUT GUIDELINES
The high speed operation of the LTC3125 demands care-
ful attention to board layout. A careless layout will result
in reduced performance. A large ground pin copper area
will help to lower the die temperature. A multilayer board
with a separate ground plane is ideal, but not absolutely
necessary.
COMPONENT SELECTION
Inductor Selection
The LTC3125 can utilize small surface mount chip induc-
tors due to its fast 1.6MHz switching frequency. Inductor
values between 2.2μH and 4.7μH are suitable for most
applications. Larger values of inductance will allow slightly
greater output current capability (and lower the Burst Mode
threshold) by reducing the inductor ripple current. Increas-
ing the inductance above 10μH will increase size while
providing little improvement in output current capability.
The minimum inductance value is given by:
V IN > V OUT OPERATION
The LTC3125 will maintain voltage regulation even when
L>
V IN(MIN) ? ( V OUT(MAX) –V IN(MIN)
Ripple ?V OUT(MAX) ?f SW
)
the input voltage is above the desired output voltage.
Note that the ef?ciency and the maximum output current
capability are reduced. Refer to the Typical Performance
Characteristics for details.
SHORT-CIRCUIT PROTECTION
The LTC3125 output disconnect feature enables output
short circuit protection although input current limit func-
tionality is maintained. To reduce power dissipation under
where:
Ripple = Allowable inductor current ripple
(amps peak-peak)
V IN(MIN) = Minimum input voltage
V OUT(MAX) = Maximum output voltage
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
3125fa
10
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