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参数资料
| 型号： | LT3507AIUHF#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PQCC38 |
| 封装： | 5 X 7 MM, LEAD FREE, PLASTIC, QFN-38 |
| 文件页数： | 5/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AIUHF#PBF |
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LT3507A
13
3507af
Electrolytic capacitors are also an option. The ESRs of
most aluminum electrolytic capacitors are too large to
deliver low output ripple. Tantalum, as well as newer,
lower-ESR organic electrolytic capacitors intended for
power supply use are suitable. Chose a capacitor with a
low enough ESR for the required output ripple. Because
the volume of the capacitor determines its ESR, both the
size and the value will be larger than a ceramic capacitor
that would give similar ripple performance. One benefit
is that the larger capacitance may give better transient
response for large changes in load current. Table 3 lists
several capacitor vendors.
Table 3. Low ESR Surface Mount Capacitors
MANUFACTURER TYPE
SERIES
Taiyo-Yuden
Ceramic
AVX
Ceramic
Tantalum
TPM, TPS
Kemet
Ceramic
Tantalum
Tantalum Organic Polymer
Aluminum Organic Polymer
T494, T495
T510, T520, T525, T530
A700
Sanyo
Tantalum Organic Polymer
Aluminum Organic Polymer
POSCAP
OS-CON
Panasonic
Ceramic
Aluminum Organic Polymer SP CAP
TDK
Ceramic
Diode Selection
The catch diode (D1 from Figure 1) conducts current only
during switch off time. Average forward current in normal
operation can be calculated from:
ID(AVG) =
IOUT VIN – VOUT
(
)
VIN
The only reason to consider a diode with a larger current
rating than necessary for nominal operation is for the
worst-case condition of shorted output. The diode current
will then increase to the typical peak switch current. Peak
reverse voltage is equal to the regulator input voltage.
Use a diode with a reverse voltage rating greater than the
input voltage. The programmable OVLO can protect the
diode from excessive reverse voltage by shutting down
the regulator if the input voltage exceeds the maximum
rating of the diode. Table 4 lists several Schottky diodes
and their manufacturers.
Table 4. Schottky Diodes
MANUFACTURER
PART
NUMBER CURRENT
VF AT
OUTLINE
On Semiconductor
MBRS240
2A
0.43V
SMB
On Semiconductor
MBRS340
3A
0.5V
SMC
On Semiconductor
MBRD340
3A
0.6V
DPAK
Diodes, Inc.
B240A
2A
0.5V
SMA
Diodes, Inc.
B340
3A
0.5V
SMC
Diodes, Inc.
SMB340
3A
0.5V
Powermite 3
Central Semiconductor CMSH3-40
3A
0.5V
SMC
Central Semiconductor CSHD3-40
3A
0.65V
DPAK
Boost Pin Considerations
The capacitor and diode tied to the BOOST pin generate
a voltage that is higher than the input voltage. In most
cases, a small ceramic capacitor and fast switching di-
ode (such as the CMDSH-3 or MMSD914LT1) will work
well. The capacitor value is a function of the switching
frequency, peak current, duty cycle and boost voltage;
in general a value of (0.1F 1MHz/fSW) works well.
Figure 3 shows three ways to arrange the boost circuit.
The BOOST pin must be more than 2.5V above the SW
pin for full efficiency. For outputs of 3.3V and higher, the
standard circuit (Figure 3a) is best. For outputs between
2.8V and 3.3V, use a small Schottky diode (such as the
BAT54). For lower output voltages, the boost diode can
be tied to the input (Figure 3b). The circuit in Figure 3a is
more efficient because the BOOST pin current comes from
a lower voltage source. Finally, as shown in Figure 3c, the
anode of the boost diode can be tied to another source
that is at least 3V. For example, if you are generating 3.3V
and 1.8V and the 3.3V is on whenever the 1.8V is on, the
1.8V boost diode can be connected to the 3.3V output. In
this case, the 3.3V output cannot be set to track the 1.8V
output (see Output Voltage Tracking).
In any case, be sure that the maximum voltage at the
BOOST pin is less than 55V and the voltage difference
between the BOOST and SW pins is less than 25V.
The minimum operating voltage of an LT3507A applica-
tion is limited by the internal undervoltage lockout and by
the maximum duty cycle. The boost circuit also limits the
minimum input voltage for proper start-up. If the input
voltage ramps slowly, or the LT3507A turns on when
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3507EUHF#2ESPBF | 制造商:Linear Technology 功能描述:TRIPLE MONOLITHIC STEP-DOWN REGULATOR WITH LDO |
| LT3507EUHF#PBF | 功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507EUHF#TRPBF | 功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507EUHFPBF | 制造商:Linear Technology 功能描述:Step Down Regulator with LDO |
| LT3507EUHF-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO |
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