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参数资料
| 型号： | LT3640EUFD#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封装： | 5 X 4 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件页数： | 4/24页 |
| 文件大小： | 506K |
| 代理商： | LT3640EUFD#PBF |
LT3640
3640f
Setting the Output Voltages
The internal reference voltage is 1.265V for the high volt-
age channel, and 600mV for the low voltage channel. The
output voltages are set by resistor dividers according to
the following formulas:
R
V
R
V
OUT
2
1
1 265
1
4
3
0 6
1
2
=
=
.
.
Use 1% resistors in the resistor dividers. To avoid noise
problems, R1 should be 100k or less, and R3 should
be 50k or less. Reference designators refer to the Block
Diagram.
Switching Frequency
The LT3640 uses a constant-frequency PWM architecture
that can be programmed to switch from 350kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. Table
1 shows the necessary RT value for a desired switching
frequency.
Table 1. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz)
RT (k)
0.35
267
0.5
182
1
82.5
2
32.4
2.2
27.4
Selection of the operating frequency is mainly a trade-off
between efficiency and component size. The advantage
of high frequency operation is that smaller inductor and
capacitor values may be used. The disadvantage is lower
efficiency.
The high switching frequency also decreases the duty
cycle range. The reason is that the LT3640 switches have
finite minimum on- and off-times independent of the
switching frequency. The top switch in the high voltage
channel can turn on for a minimum of ~60ns and turn off
for a minimum of ~70ns. The top switch in the low voltage
channel can turn on for a minimum of ~110ns and turn
applicaTions inForMaTion
off for a minimum of ~70ns. The minimum and maximum
duty cycles are:
DCMIN = fS tON(MIN)
DCMAX = 1 – fS tOFF(MIN)
where fS is the switching frequency, tON(MIN) is the mini-
mum switch on-time, and tOFF(MIN) is the minimum switch
off-time. These equations illustrate how duty cycle range
increases when switching frequency decreases.
The internal oscillator of the LT3640 can be synchronized
to an external 350kHz to 2.5MHz positive clock signal on
the SYNC pin. The RT value should be chosen such that
the internal oscillator’s frequency is 20% lower than the
lowest SYNC clock frequency (refer to Table 1). To avoid
erratic operation, the LT3640 ignores the SYNC signal
until the FB1 pin voltage is above 1.165V. When applying
a SYNC signal, the rising edges reset the LT3640’s internal
clock and initiate a switch cycle. The amplitude of the
SYNC signal must be at least 2V. The SYNC pulse width
must be at least 40ns.
VIN Voltage Range
The LT3640’s minimum operating voltage is 3.6V typical.
A higher minimum operating voltage can be accurately
programmed with a resistor divider between the VIN pin
and the EN/UVLO pin. The EN/UVLO threshold is 1.26V.
When the LT3640 is enabled, a 2A current flows out of the
EN/UVLO pin generating hysteresis to prevent the switch-
ing action from falsely disabling the LT3640. Choose the
divider resistances for appropriate hysteresis voltage.
The high voltage nonsynchronous channel operates from
the VIN pin. The minimum VIN voltage to regulate output
voltage is:
V
DC
V
IN MIN
OUT
D
MAX
D
CE
(
) =
+
+
1
WhereVDistheforwardvoltagedropofthecatchdiode,VCE
is the voltage drop of the internal NPN power switch, and
DCMAX is the maximum duty cycle (refer to the Switching
Frequencysection).IfVINisbelowthecalculatedminimum
voltage, output will lose regulation.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3640EUFDTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer |
| LT3640IFE | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer |
| LT3640IFE#PBF | 功能描述:IC REG BUCK FIX/ADJ DL 28TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 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:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT3640IFE#TRPBF | 功能描述:IC REG BUCK FIX/ADJ DL 28TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 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:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT3640IFEPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer |
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