参数资料
型号: LT1375CS8-5#TR
厂商: Linear Technology
文件页数: 15/28页
文件大小: 0K
描述: IC REG BUCK 5V 1.5A 8SOIC
标准包装: 2,500
类型: 降压(降压)
输出类型: 固定
输出数: 1
输出电压: 5V
输入电压: 5 V ~ 25 V
PWM 型: 电流模式
频率 - 开关: 500kHz
电流 - 输出: 1.5A
同步整流器:
工作温度: 0°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
包装: 带卷 (TR)
供应商设备封装: 8-SOIC
LT1375/LT1376
APPLICATIO N S I N FOR M ATIO N
R FB
LT1375/LT1376
INPUT
IN
2.38V
+
V SW
OUTPUT
STANDBY
R HI
SHDN
3.5 μ A
+
TOTAL
SHUTDOWN
+
C1
R LO
0.37V
GND
1375/76 F04
Figure 4. Undervoltage Lockout
R LO [ IN ( OUT + 1 ) + ? V
(
)
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where these problems might occur.
Threshold voltage for lockout is about 2.38V, slightly less
than the internal 2.42V reference voltage. A 3.5 μ A bias
R HI =
V ? 2 . 38 ? V / V
2 . 38 ? R 2 3 . 5 μ A
R FB = ( R HI )( V OUT / ? V )
]
R LO ( IN ? 2 . 38 V )
(
)
[ ( ) ]
2 . 38 ? 25 k ( )
(
)
current flows out  of the pin at threshold. This internally
generated current is used to force a default high state on
the shutdown pin if the pin is left open. When low shut-
down current is not an issue, the error due to this current
can be minimized by making R LO 10k or less. If shutdown
current is an issue, R LO can be raised to 100k, but the error
due to initial bias current and changes with temperature
should be considered.
R LO = 10 k to 100k ( 25k suggested )
V
R HI =
2 . 38 V ? R LO 3 . 5 μ A
V IN = Minimum input voltage
Keep the connections from the resistors to the shutdown
pin short and make sure that interplane or surface capaci-
tance to the switching nodes are minimized. If high resis-
tor values are used, the shutdown pin should be bypassed
with a 1000pF capacitor to prevent coupling problems
from the switch node. If hysteresis is desired in the
undervoltage lockout point, a resistor R FB can be added to
the output node. Resistor values can be calculated from:
25k suggested for R LO
V IN = Input voltage at which switching stops as input
voltage descends to trip level
? V = Hysteresis in input voltage level
Example: output voltage is 5V, switching is to stop if input
voltage drops below 12V and should not restart unless
input rises back to 13.5V. ? V is therefore 1.5V and V IN =
12V. Let R LO = 25k.
25 k 12 ? 2 . 38 1 . 5 / 5 + 1 + 1 . 5
R HI =
3 . 5 μ A
= 25 k ( 10 . 41 ) = 114 k
2 . 29
R FB = 114 k 5 / 1 . 5 = 380 k
SWITCH NODE CONSIDERATIONS
For maximum efficiency, switch rise and fall times are
made as short as possible. To prevent radiation and high
frequency resonance problems, proper layout of the com-
ponents connected to the switch node is essential. B field
13756fd
15
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