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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： | 2/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AIUHF#PBF |
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LT3507A
10
3507af
APPLICATIONS INFORMATION
STEP-DOWN CONSIDERATIONS
FB Resistor Network
The output voltage is programmed with a resistor divider
(refer to the Block Diagram) between the output and the
FB pin. Choose the resistors according to:
R1
=R2
VOUT
800mV
– 1
The parallel combination of R1 and R2 should be 10k or
less to avoid bias current errors.
Input Voltage Range
The minimum operating voltage is determined either by
the LT3507A’s internal undervoltage lockout (4V on VIN1,
3V on VIN2 and VIN3) or by its maximum duty cycle. The
duty cycle is the fraction of time that the internal switch
is on and is determined by the input and output voltages:
DC
=
VOUT + VF
VIN – VSW + VF
where VF is the forward voltage drop of the catch diode
(~0.4V) and VSW is the voltage drop of the internal switch
(~0.3V at maximum load). This leads to a minimum input
voltage of:
VIN(MIN) =
VOUT + VF
DCMAX
– VF + VSW
Thedutycycleisthefractionoftimethattheinternalswitch
is on during a clock cycle. The maximum duty cycle is
generally given by DCMAX = 1– tOFF(MIN) fSW. However,
unlike most fixed frequency regulators, the LT3507A will
not switch off at the end of each clock cycle if there is suf-
ficient voltage across the boost capacitor (C3 in Figure 1)
to fully saturate the output switch. Forced switch off for
a minimum time will only occur at the end of a clock
cycle when the boost capacitor needs to be recharged.
This operation has the same effect as lowering the clock
frequency for a fixed off time, resulting in a higher duty
cycleandlowerminimuminputvoltage.Theresultantduty
cycle depends on the charging times of the boost capaci-
tor and can be approximated by the following equation:
DCMAX =
1
+
1
B
where B is the output current capacity divided by the typi-
cal boost current from the BOOST pin current vs switch
currentintheTypicalPerformanceCharacteristicssection.
The maximum operating voltage without pulse-skipping
is determined by the minimum duty cycle DCMIN:
VIN(PS) =
VOUT + VF
DCMIN
– VF + VSW
with DCMIN = tON(MIN) fSW.
Thus both the maximum and minimum input voltages are
a function of the switching frequency and output voltages.
Therefore the maximum switching frequency must be set
to a value that accommodates all the input and output
voltage parameters and must meet both of the following
criteria for each channel:
fMAX1=
VOUT + VF
VIN(PS) – VSW + VF
1
tON(MIN)
fMAX2 = 1–
VOUT + VF
VIN(MIN) – VSW + VF
1
tOFF(MIN)
The values of tON(MIN) and tOFF(MIN) are functions of ISW
and temperature (see chart in the Typical Performance
Characteristics section). Worst-case values for switch
currents greater than 0.5A are tON(MIN) = 130ns (for TJ >
125°C tON(MIN) = 155ns) and tOFF(MIN) = 170ns.
fMAX1 is the frequency at which the minimum duty cycle
is exceeded. The regulator will skip ON pulses in order to
reduce the overall duty cycle at frequencies above fMAX1.
It will continue to regulate but with increased inductor
current and greatly increased output ripple. The increased
peak inductor current in pulse-skipping will also stress
the switch transistor at high voltages and high switching
frequency. If the LT3507A is allowed to pulse-skip and
the input voltage is greater than 20V, then the switching
frequency must be kept below 1.1MHz to prevent damage
to the LT3507A.
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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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