- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄377683 > LT1111M (Linear Technology Corporation) Dual 4-Input Positive-NAND Gates 14-SO 0 to 70 PDF資料下載
參數(shù)資料
| 型號： | LT1111M |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Dual 4-Input Positive-NAND Gates 14-SO 0 to 70 |
| 中文描述： | 微功率DC / DC轉(zhuǎn)換可調(diào)和固定5V，12V的 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大小： | 337K |
| 代理商： | LT1111M |
12
LT1111
U
S
A
O
PPLICATI
IU
U
L1
LT1111 F08
GND
SW2
FB
SW1
LIM
I
IN
V
D1
A0
V
OUT
R2
V
OUT
= R1
R1
2N3906
–V
IN
+
C1
LT1111
+
C2
Figure 8. Negative-to-Positive Converter
Using the I
LIM
Pin
The LT1111 switch can be programmed to turn off at a set
switch current, a feature not found on competing devices.
This enables the input to vary over a wide range without
exceeding the maximum switch rating or saturating the
inductor. Consider the case wh ere analysis shows the
LT1111 must operate at an 800mA peak switch current
with a 2V input. If V
IN
rises to 4V, the peak switch current
will rise to 1.6A, exceeding the maximum switch current
rating. With the proper resistor selected (see the “Maxi-
mum Switch
Current vs I
LIM
” characteristic), the switch
current will be limited to 800mA, even if the input voltage
increases.
Another situation where the I
LIM
feature is useful occurs
when the device goes into continuous mode operation.
This occurs in step-up mode when:
V
V
V
V
DC
OUT
DIODE
IN
SW
+
<
1
1
25
(
)
When the input and output voltages satisfy this relation-
ship, inductor current does not go to zero during the
switch OFF time. When the switch turns on again, the
current ramp starts from the non-zero current level in the
inductor just prior to switch turn-on. As shown in Figure
9, the inductor current increases to a high level before the
comparator turns off the oscillator. This high current can
cause excessive output ripple and requires oversizing the
output capacitor and inductor. With the I
LIM
feature,
however, the switch current turns off at a programmed
level as shown in Figure 10, keeping output ripple to a
minimum.
LT1111 F09
I
OFF
L
ON
SWITCH
Figure 9. No Current Limit Causes Large Inductor
Current Build-Up
LT1111 F10
I
ON
OFF
L
SWITCH
PROGRAMMED CURRENT LIMIT
Figure 10. Current Limit Keeps Inductor Current Under Control
Figure 11 details current limit circuitry. Sense transistor
Q1, whose base and emitter are paralleled with power
switch Q2, is ratioed such that approximately 0.5% of
Q2’s collector current flows in Q1’s collector. This current
is passed through internal 80
resistor R1 and out
through the I
LIM
pin. The value of the external resistor
connected between I
LIM
and V
IN
sets the current limit.
When sufficient switch current flows to develop a V
BE
across R1 + R
LIM
, Q3 turns on and injects current into the
oscillator, turning off the switch. Delay through this cir-
cuitry is approximately 1
μ
s. The current trip point be-
comes less accurate for switch ON times less than 3
μ
s.
Resistor values programming switch ON time for 1
μ
s or
less will cause spurious response in the switch circuitry
although the device will still maintain output regulation.
LT1111 F11
SW2
SW1
DRIVER
OSCILLATOR
V
IN
I
LIM
R1
80
(INTERNAL)
R
(EXTERNAL)
Q1
Q2
Q3
Figure 11. LT1111 Current Limit Circuitry
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LT1111MJ8-5 | Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| LT1113ACN8 | Dual Low Noise, Precision, JFET Input Op Amps |
| LT1113 | Dual Low Noise, Precision, JFET Input Op Amps |
| LT1113AC | Dual Low Noise, Precision, JFET Input Op Amps |
| LT1113AM | Dual Low Noise, Precision, JFET Input Op Amps |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT1111MJ8 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| LT1111MJ8-12 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| LT1111MJ8-5 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| LT1112 | 制造商:LINEAR 制造商全稱:LINEAR 功能描述:Dual/Quad Low Power Precision, Picoamp Input Op Amps |
| LT1112_1 | 制造商:LINEAR 制造商全稱:LINEAR 功能描述:Dual/Quad Low Power Precision, Picoamp Input Op Amps |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。