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参数资料
| 型号： | LT3501EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/30页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A DL 20TSSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 23.8 V |
| 输入电压： | 3.1 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 250kHz ~ 1.5MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 20-TSSOP-EP |
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LT3501
APPLICATIONS INFORMATION
DC MAX =
1 +
V IN(MIN) = OUT
– V D + V SW
DC MAX =
= 98%
1 +
V IN(MIN) =
– 0.4 + 0.1 = 3.48V
V IN(MAX) =
– 0.4 + 0.1 = 18.2V
dutycycle.Thedutycycleisthefractionoftimethatthe
internal switch is on during a clock cycle. Unlike most
fixed frequency regulators, the LT3501 will not switch off
at the end of each clock cycle if there is sufficient voltage
across the boost capacitor (C3 in Figure 1) to fully satu-
rate 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 cycle and lower
minimum input voltage. The resultant duty cycle depends
on the charging times of the boost capacitor and can be
approximated by the following equation:
1
1
B
where B is 3A divided by the typical boost current from
the Electrical Characteristics table.
This leads to a minimum input voltage of:
V + V D
DC MAX
where V SW is the voltage drop of the internal switch.
Figure 3 shows a typical graph of minimum input voltage
vs load current for the 3.3V and 1.8V application on the
first page of this data sheet. The maximum input voltage
is determined by the absolute maximum ratings of the V IN
and BST pins and by the frequency and minimum duty
cycle. The minimum duty cycle is defined as :
DC MIN = t ON(MIN) ? Frequency
Maximum input voltage as:
6.0
V OUT = 3.3V
5.5
5.0
START-UP
4.5
4.0
3.5
RUNNING
3.0
1 10 100 1000 10000
CURRENT (mA)
3501 F03
Figure 3. Minimum Input Voltage vs Load Current
Example:
V OUT = 3.3V, I OUT = 1A, Frequency = 1MHz, Temperature
= 25°C
V SW = 0.1V, B = 50 (from from boost characteristics
specification), V D = 0.4V, t ON(MIN) = 200ns
1
1
50
3.3 + 0.4
0.98
DC MIN = t MIN(ON) ? f = 0.200
3.3 + 0.4
0.200
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
V IN(MAX) =
V OUT + V D
DC MIN
– V D + V SW
L =
( V IN – V OUT ) ? V OUT
V IN ? f
Note that the LT3501 will regulate if the input voltage is
taken above the calculated maximum voltage as long as
maximum ratings of the V IN and BST pins are not violated.
However operation in this region of input voltage will exhibit
pulse skipping behavior.
where f is frequency in MHz and L is in μH.
With this value the maximum load current will be ~3A,
independent of input voltage. The inductor’s RMS current
rating must be greater than your maximum load current
3501fd
13
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