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参数资料
| 型号： | LT3825EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 19/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO 16-TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 88% |
| 电源电压： | 11 V ~ 18 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
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LT3825
APPLICATIONS INFORMATION
R A =
R B =
? V IN(ON) ?
The bias current on this pin depends on the pin volt-
age and UVLO state. The change provides the user with
adjustable UVLO hysteresis. When the pin rises above
the UVLO threshold a small current is sourced out of the
pin, increasing the voltage on the pin. As the pin voltage
drops below this threshold, the current is stopped, further
dropping the voltage on UVLO. In this manner, hysteresis
is produced.
Referring to Figure 3, the voltage hysteresis at V IN is
equal to the change in bias current times R A . The design
procedure is to select the desired V IN referred voltage
hysteresis, V UVHYS . Then:
V UVHYS
I UVLO
where:
I UVLO = I UVLOL – I UVLOH is approximately 3.4μA
R B is then selected with the desired turn-on voltage:
R A
? – 1 ?
? V UVLO ?
If we wanted a V IN -referred trip point of 36V, with 1.8V
(5%) of hysteresis (on at 36V, off at 34.2V):
Even with good board layout, board noise may cause
problems with UVLO. You can filter the divider but keep
large capacitance off the UVLO node because it will slow
the hysteresis produced from the change in bias current.
Figure 3c shows an alternate method of filtering by split-
ting the R A resistor with the capacitor. The split should
put more of the resistance on the UVLO side.
Converter Start-Up
The standard topology for the LT3825 utilizes a third
transformer winding on the primary side that provides both
feedback information and local V CC power for the LT3825
(see Figure 4). This power “bootstrapping” improves
converter efficiency but is not inherently self-starting.
Start-up is affected with an external “trickle-charge” resis-
tor and the LT3825’s internal V CC undervoltage lockout
circuit. The V CC undervoltage lockout has wide hysteresis
to facilitate start-up.
In operation, the “trickle charge” resistor, R TR , is con-
nected to V IN and supplies a small current, typically on the
order of 1mA to charge C TR . Initially the LT3825 is off and
draws only its start-up current. When C TR reaches the V CC
turn-on threshold voltage the LT3825 turns on abruptly
and draws its normal supply current.
R A = 1.8V = 529k, use 523k
3.4 μ A
V IN
R TR
?
? 36V ?
? 1.23V
?
R B =
? – 1 ?
523k
= 18.5k, use 18.7k
+
C TR
V CC
I VCC
V IN
?
?
LT3825
PG
V IN
GND
I UVLO
I UVLO
R A1
V IN
R A
R B
UVLO
LT3825
V IN
R A
R B
UVLO
LT3825
C UVLO
R A2
UVLO
R B
V ON THRESHOLD
V VCC
I VCC
0
(3a) UV Turning ON
(3b) UV Turning OFF
3825 F03
(3c) UV Filtering
V PG
3825 F04
Figure 3
Figure 4. Typical Power Bootstrapping
3825fe
19
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT382B | 制造商:EDSYN 功能描述:TIP CONICAL 0.5X15.8MM |
| LT383 | 制造商:EDSYN 功能描述: |
| LT3837 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Low VIN, 8A DC/DC μModule Regulator |
| LT3837EFE | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 16-Pin TSSOP EP |
| LT3837EFE#PBF | 功能描述:IC REG CTRLR FLYBK ISO 16-TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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