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| 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： | 11/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AIUHF#PBF |
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LT3507A
19
3507af
voltageissubstantiallyhigherthan0.8Vatsteadystateand
effectively turns off D1. D2 and D3 will therefore conduct
the same current and offer tight matching between VFB2
andtheinternalprecision0.8Vreference.Intheratiometric
mode with R6 = R2, TRK/SS2 equals 0.8V at steady state.
D1willdivertpartofthebiascurrentandmakeVFB2slightly
lower than 0.8V. Although this error is minimized by the
exponentialI-Vcharacteristicofthediodes,itdoesimpose
a finite amount of output voltage deviation. Further, when
channel1’soutputexperiencesdynamicexcursions(under
load transient, for example), channel 2 will be affected as
well.SettingR6toavaluethatpushestheTRK/SS2voltage
to 1V at steady state will eliminate these problems while
providing near ratiometric tracking.
Theexampleshowschannel2trackingchannel1,however
any channel may be set up to track any other channel.
If a capacitor is tied from the TRK/SS pin to ground, then
the internal pull-up current will generate a voltage ramp on
this pin. This results in a ramp at the output, limiting the
inductorcurrentandthereforeinputcurrentduringstart-up.
A good value for the soft-start capacitor is COUT/10,000,
where COUT is the value of the output capacitor.
MULTIPLE INPUT SUPPLIES
VIN1, VIN2 and VIN3 are independent and can be powered
with different voltages provided VIN1 is present when VIN2
or VIN3 is present. Each supply must be bypassed as close
to the VIN pins as possible.
For applications requiring large inductors due to high VIN
to VOUT ratios, a 2-stage step-down approach may reduce
inductor size by allowing an increase in frequency. A dual
step-down application steps down the input voltage (VIN1)
to the highest output voltage, then uses that voltage to
power the other outputs (VIN2 and VIN3). VOUT1 must be
able to provide enough current for its output plus the
input current at VIN2 and VIN3 when VOUT2 and VOUT3 are
at maximum load. The Typical Applications section shows
a 36V to 15V, 1.8V and 1.2V 2-stage converter using this
approach.
For applications with multiple voltages, the LT3507A can
accommodate input voltages as low as 3V on VIN2 and
APPLICATIONS INFORMATION
VIN3. This can be useful in applications regulating outputs
from a PCI Express bus, where the 12V input is power
limited and the 3.3V input has power available to drive
other outputs. In this case, tie the 12V input to VIN1 and
the 3.3V input to VIN2 and VIN3.
LOW DROPOUT REGULATOR
The low dropout regulator comprises an error amp, loop
compensation and a base drive amp. It uses the same 0.8V
referenceastheswitchingregulators.Itrequiresanexternal
NPN pass transistor and 2.2F of output capacitance for
stability. The internal compensation is stable with loads
up to 300mA.
The dropout characteristics will be determined by the pass
transistor. The collector-emitter saturation characteristics
will limit the dropout voltage. Table 5 lists some suitable
NPN transistors with their saturation specifications.
The base drive voltage has a maximum voltage of 5V.
This will limit the maximum output of the regulator to
5V – VBESAT where VBESAT is the base-emitter saturation
voltage of the pass transistor.
Table 5. Low VCESAT Transistors
PART NUMBER
VCESAT AT
IC = 1A
OUTLINE
MANUFACTURER
ZXTN25012EZ
0.06
SOT89
Zetex
www.diodes.com
ZXTN25020DG
0.075
SOT223
NSS20201JT1G
0.22
SC-89
On Semiconductor
www.onsemi.com
NSS12201LT1G
0.08
SOT-23
CTLT3410-M621
0.28
1mm
× 2mm
TLM621
Central Semiconductor
www.central-semi.com
The LDO is always on when any of the switcher channels
is on. The LDO may be shut down if it is unused by pull-
ing the FB4 pin up with a 30A current source. The FB4
pin will clamp at about 1.25V and the LDO will shut off
reducingpowerconsumption.Thispull-upcanbesourced
from one of the LT3507A outputs provided that channel is
always on when the other channels are on.
The output stage of the LDO will drive the NPN base from
the BIAS voltage if it is at least 0.8V above the LDO DRIVE
voltage.
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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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