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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： | 7/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AIUHF#PBF |
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LT3507A
15
3507af
if the system can tolerate a few mA of load in this state.
With all three RUN pins grounded, the LT3507A enters
shutdown mode and the SW pin current drops to <50A.
However, if the VIN pin is grounded while the output is held
high, then parasitic diodes inside the LT3507A can pull
large currents from the output through the SW pin and the
VIN pin. A Schottky diode in series with the input to the
LT3507A, as shown in Figure 5, will protect the LT3507A
and the system from a shorted or reversed input.
and is largest when VIN = 2VOUT (50% duty cycle). As
the second, lower power channel draws input current,
the input capacitor’s RMS current actually decreases as
the out-of-phase current cancels the current drawn by the
higherpowerchannel.Consideringthatthemaximumload
current from a single phase (if SW2 and SW3 are both
at maximum current) is ~3.6A, RMS ripple current will
always be less than 1.8A.
The high frequency of the LT3507A reduces the energy
storage requirements of the input capacitor, so that the
capacitance required is often less than 10F. The combi-
nation of small size and low impedance (low equivalent
series resistance or ESR) of ceramic capacitors makes
them the preferred choice. The low ESR results in very
low voltage ripple. Ceramic capacitors can handle larger
magnitudes of ripple current than other capacitor types
of the same value. Use X5R and X7R types.
An alternative to a high value ceramic capacitor is a lower
value along with a larger electrolytic capacitor, for example
a 1F ceramic capacitor in parallel with a low ESR tantalum
capacitor. For the electrolytic capacitor, a value larger than
10F will be required to meet the ESR and ripple current
requirements. Because the input capacitor is likely to see
high surge currents when the input source is applied, tan-
talum capacitors should be surge rated. The manufacturer
may also recommend operation below the rated voltage
of the capacitor. Be sure to place the 1F ceramic as close
as possible to the VIN and GND pins on the IC for optimal
noise immunity.
A final caution is in order regarding the use of ceramic
capacitors at the input. A ceramic input capacitor can
combine with stray inductance to form a resonant tank
circuit.Ifpowerisappliedquickly(forexamplebyplugging
the circuit into a live power source), this tank can ring,
doublingtheinputvoltageanddamagingtheLT3507A.The
solution is to either clamp the input voltage or dampen the
tank circuit by adding a lossy capacitor in parallel with the
ceramic capacitor. For details, see Application Note 88.
APPLICATIONS INFORMATION
Figure 5. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output
VIN
VOUT
SW
LT3507A
D4
PARASITIC DIODE
3507A F05
Input Capacitor Selection
Bypass the input of the LT3507A circuit with a 10F or
higherceramiccapacitorofX7RorX5Rtype.Thefollowing
paragraphs describe the input capacitor considerations
in more detail.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
at the LT3507A input and to force this switching current
into a tight local loop, minimizing EMI. The input capaci-
tor must have low impedance at the switching frequency
to do this effectively and it must have an adequate ripple
current rating. With three switchers operating at the same
frequency but with different phases and duty cycles, cal-
culating the input capacitor RMS current is not simple;
however, a conservative value is the RMS input current
for the phase delivering the most power (VOUT IOUT):
IIN(RMS) = IOUT
VOUT VIN – VOUT
(
)
VIN
<
IOUT
2
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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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