参数资料
| 型号： | LT1938IDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2.2A 10DFN |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.27 V ~ 20 V |
| 输入电压： | 3.6 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 300kHz ~ 2.8MHz |
| 电流 - 输出： | 2.2A |
| 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： | 10-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-DFN（3x3） |
LT1938
APPLICATIONS INFORMATION
L = ? OUT
? V + V D ? ? V + V D ?
? ? ?
V IN ( MIN ) =
V OUT + V D
1– f SW t OFF ( MIN )
frequencywillbenecessarytoachievesafeoperationat
high input voltages.
If the output is in regulation and no short-circuit or start-up
events are expected, then input voltage transients of up to
25V are acceptable regardless of the switching frequency.
In this mode, the LT1938 may enter pulse skipping opera-
tion where some switching pulses are skipped to maintain
output regulation. In this mode the output voltage ripple
and inductor current ripple will be higher than in normal
operation.
The minimum input voltage is determined by either the
LT1938’s minimum operating voltage of ~3.6V or by its
maximum duty cycle (see equation in previous section).
The minimum input voltage due to duty cycle is:
– V D + V SW
where V IN(MIN) is the minimum input voltage, and t OFF(MIN)
is the minimum switch off time (150ns). Note that higher
switching frequency will increase the minimum input
voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current ? I L increases with higher V IN or V OUT
and decreases with higher inductance and faster switch-
ing frequency. A reasonable starting point for selecting
the ripple current is:
? I L = 0.4(I OUT(MAX) )
where I OUT(MAX) is the maximum output load current. To
guarantee sufficient output current, peak inductor current
must be lower than the LT1938’s switch current limit (I LIM ).
The peak inductor current is:
I L(PEAK) = I OUT(MAX) + ? I L /2
at least 3.5A at low duty cycles and decreases linearly to
2.5A at DC = 0.8. The maximum output current is a func-
tion of the inductor ripple current:
I OUT(MAX) = I LIM – ? I L /2
Be sure to pick an inductor ripple current that provides
sufficient maximum output current (I OUT(MAX) ).
The largest inductor ripple current occurs at the highest
V IN . To guarantee that the ripple current stays below the
specified maximum, the inductor value should be chosen
according to the following equation:
?
? 1– OUT ?
? f Δ I L ? V IN ( MAX ) ?
where V D is the voltage drop of the catch diode (~0.4V),
V IN(MAX) is the maximum input voltage, V OUT is the output
voltage, f SW is the switching frequency (set by R T ), and L
is in the inductor value.
The inductor’s RMS current rating must be greater than the
maximum load current and its saturation current should be
about 30% higher. For robust operation in fault conditions
(start-up or short circuit) and high input voltage (>30V),
the saturation current should be above 3A. To keep the
efficiency high, the series resistance (DCR) should be less
than 0.1Ω, and the core material should be intended for
high frequency applications. Table 1 lists several vendors
and suitable types.
Table 1. Inductor Vendors
VENDOR URL PART SERIES TYPE
Murata www.murata.com LQH55D Open
TDK www.componenttdk.com SLF7045 Shielded
SLF10145 Shielded
Toko www.toko.com D62CB Shielded
D63CB Shielded
D75C Shielded
D75F Open
Sumida www.sumida.com CR54 Open
where I L(PEAK) is the peak inductor current, I OUT(MAX) is
the maximum output load current, and ? I L is the inductor
ripple current. The LT1938’s switch current limit (I LIM ) is
CDRH74
CDRH6D38
CR75
Shielded
Shielded
Open
1938fa
11
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| LT1939EDD#PBF | 功能描述:IC REG DL BUCK/LINEAR 12DFN 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:* |
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