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参数资料
| 型号： | LT1765-1.8 |
| 厂商： | Linear Technology Corporation |
| 元件分类： | 基准电压源/电流源 |
| 英文描述： | Isolated Flyback Switching Regulator with 9V Output |
| 中文描述： | 隔离反激式开关稳压9V输出 |
| 文件页数： | 8/20页 |
| 文件大小： | 247K |
| 代理商： | LT1765-1.8 |
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
8
sn1765 1765fas
FB RESISTOR NETWORK
If an output voltage of 1.8V, 2.5V, 3.3V or 5V is required,
the respective fixed option part, -1.8, -2.5, -3.3 or -5,
should be used. The FB pin is tied directly to the output; the
necessary resistive divider is already included on the part.
For other voltage outputs, the adjustable part should be
used and an external resistor divider added. The sug-
gested resistor (R2) from FB to ground is 10k. This
reduces the contribution of FB input bias current to output
voltage to less than 0.25%. The formula for the resistor
(R1) from V
OUT
to FB is:
R
R V
2
1. –
R
A
OUT
20 25
( .
1
1 2
μ
=
(
– . )
)
–
+
1.2V
V
SW
V
C
GND
1765 F02
R1
R2
10k
OUTPUT
ERROR
AMPLIFIER
FB
LT1765 (ADJ)
+
Figure 2. Feedback Network
APPLICATIOU
W
U
U
rating and turn-on surge problems. Y5V or similar type
ceramics can be used since the absolute value of capaci-
tance is less important and has no significant effect on
loop stability. If operation is required close to the mini-
mum input required by the output or the LT1765, a larger
value may be required. This is to prevent excessive ripple
causing dips below the minimum operating voltage result-
ing in erratic operation.
If tantalum capacitors are used, values in the 22
μ
F to 470
μ
F
range are generally needed to minimize ESR and meet
ripple current and surge ratings. Care should be taken to
ensure the ripple and surge ratings are not exceeded. The
AVX TPS and Kemet T495 series tantalum capacitors are
surge rated. AVX recommends derating capacitor operat-
ing voltage by 2:1 for high surge applications.
OUTPUT CAPACITOR
Unlike the input capacitor, RMS ripple current in the
output capacitor is normally low enough that ripple cur-
rent rating is not an issue. The current waveform is
triangular, with an RMS value given by:
I
V
V
V
( )( )(
RIPPLE RMS
OUT
IN
OUT
IN
)
=
(
)
)
(
)
0 29
.
The LT1765 will operate with both ceramic and tantalum
output capacitors. Ceramic capacitors are generally cho-
sen for their small size, very low ESR (effective series
resistance), and good high frequency operation. Ceramic
output capacitors in the 1
μ
F to 10
μ
F range, X7R or X5R
type are recommended.
Tantalum capacitors are usually chosen for their bulk
capacitance properties, useful in high transient load appli-
cations. ESR rather than absolute value defines output
ripple at 1.25MHz. Typical LT1765 applications require a
tantalum capacitor with less than 0.3
ESR at 22
μ
F to
500
μ
F, see Table 2. This ESR provides a useful zero in the
frequency response. Ceramic output capacitors with low
ESR usually require a larger V
C
capacitor or an additional
series R to compensate for this.
INPUT CAPACITOR
Step-down regulators draw current from the input supply
in pulses. The rise and fall times of these pulses are very
fast. The input capacitor is required to reduce the voltage
ripple at the input of LT1765 and to force the switching
current into a tight local loop, thereby minimizing EMI. The
RMS ripple current can be calculated from:
I
I
V
V
V
V
RIPPLE RMS
OUT
OUT
IN
OUT
IN
)
=
(
)
/
2
Ceramic capacitors are ideal for input bypassing. At higher
switching frequency, the energy storage requirement of
the input capacitor is reduced so values in the range of 1
μ
F
to 4.7
μ
F are suitable for most applications. Their high
frequency capacitive nature removes most ripple current
相关PDF资料 |
PDF描述 |
|---|---|
| LT1765-3.3 | CONTACT |
| LT1765-5 | TERMINAL |
| LT1765 | Isolated Flyback Switching Regulator with 9V Output |
| LT1765-2.5 | Isolated Flyback Switching Regulator with 9V Output |
| LT1767-2.5 | Direct mounting on the PCB, Crimping connection, Discrete wire connectors; HRS No: 544-0063-6 00; No. of Positions: 15; Connector Type: Wire; Contact Gender: Male; Contact Spacing (mm): 2; Terminal Pitch (mm): 2; Termination Style: IDC; Current Rating(Amps)(Max.): 1; Contact Mating Area Plating: Tin; Operating Temperature Range (degrees C): -30 to 85; General Description: Housing; Straight; Direct PCB mounting; For AWG#26 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1765-2.5 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 3A, 1.25MHz Step-Down Switching Regulator |
| LT1765-3.3 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 3A, 1.25MHz Step-Down Switching Regulator |
| LT1765-5 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 3A, 1.25MHz Step-Down Switching Regulator |
| LT1765EFE | 功能描述:IC REG BUCK ADJ 3A 16TSSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1765EFE#PBF | 功能描述:IC REG BUCK ADJ 3A 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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