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參數(shù)資料
| 型號(hào)： | LT1107CS8-5#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | 1.5 A SWITCHING REGULATOR, 88 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁(yè)數(shù)： | 16/16頁(yè) |
| 文件大?。?/td> | 207K |
| 代理商： | LT1107CS8-5#TR |
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9
LT1107
1107fa
U
S
A
O
PPLICATI
WU
U
I FOR ATIO
I
V
L
t
PEAK
IN
ON
=( )
20
The usual step-up configuration for the LT1107 is shown
in Figure 1. The LT1107 first pulls SW1 low causing VIN –
VCESAT to appear across L1. A current then builds up in L1.
At the end of the switch ON time the current in L1 is1:
Figure 2. Step-Down Mode Hookup
D1
L1
R3
ILIM
VIN
FB
SW1
SW2
GND
C1
LT1107
1107 F01
VIN
VOUT
R2
R1
+
D1
1N5818
L1
R3
100
ILIM
VIN
FB
SW2
GND
C1
LT1107
1107 F02
VIN
VOUT
R2
R1
SW1
C2
+
Immediately after switch turn-off, the SW1 voltage pin
starts to rise because current cannot instantaneously stop
flowing in L1. When the voltage reaches VOUT + VD, the
inductor current flows through D1 into C1, increasing
VOUT. This action is repeated as needed by the LT1107 to
keep VFB at the internal reference voltage of 1.25V. R1 and
R2 set the output voltage according to the formula:
Step-Down (Buck Mode) Operation
A step-down DC/DC converter converts a higher voltage to
a lower voltage. The usual hookup for an LT1107 based
step-down converter is shown in Figure 2.
When the switch turns on, SW2 pulls up to VIN – VSW. This
puts a voltage across L1 equal to VIN – VSW – VOUT,
causing a current to build up in L1. At the end of the switch
ON time, the current in L1 is equal to:
Figure 1. Step-Up Mode Hookup
V
R
V
OUT =+
()
1
2
1
125
21
.( )
I
V
VV
L
t
PEAK
IN
SW
OUT
ON
=
()
22
When the switch turns off, the SW2 pin falls rapidly and
actually goes below ground. D1 turns on when SW2
reaches 0.4V below ground.
D1 MUST BE A SCHOTTKY
DIODE. The voltage at SW2 must never be allowed to go
below –0.5V. A silicon diode such as the 1N4933 will allow
SW2 to go to –0.8V, causing potentially destructive power
dissipation inside the LT1107. Output voltage is deter-
mined by:
R3 programs switch current limit. This is especially im-
portant in applications where the input varies over a wide
range. Without R3, the switch stays on for a fixed time
each cycle. Under certain conditions the current in L1 can
build up to excessive levels, exceeding the switch rating
and/or saturating the inductor. The 100
resistor pro-
grams the switch to turn off when the current reaches
approximately 700mA. When using the LT1107 in step-
down mode, output voltage should be limited to 6.2V or
less. Higher output voltages can be accommodated by
inserting a 1N5818 diode in series with the SW2 pin
(anode connected to SW2).
Inverting Configurations
The LT1107 can be configured as a positive-to-negative
converter (Figure 3), or a negative-to-positive converter
(Figure 4). In Figure 3, the arrangement is very similar to
a step-down, except that the high side of the feedback is
referred to ground. This level shifts the output negative. As
in the step-down mode, D1 must be a Schottky diode, and
V
R
V
OUT =+
()
1
2
1
125
23
.( )
Note 1: This simple expression neglects the effects of switch and coil
resistance. This is taken into account in the “Inductor Selection” section.
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| LT1107IS8 | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC RoHS:否 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類(lèi)型:降壓（降壓） 輸出類(lèi)型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開(kāi)關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類(lèi)型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤(pán) 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤(pán) |
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