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参数资料
| 型号： | LT1683 |
| 厂商： | Linear Technology Corporation |
| 英文描述： | Ultralow Noise Push-Pull DC/DC Controller |
| 中文描述： | 超低噪声推挽式DC / DC控制器 |
| 文件页数： | 17/24页 |
| 文件大小： | 237K |
| 代理商： | LT1683 |
17
LT1683
1683f
APPLICATIU
The soft-start current will be initiated as soon as the part
turns on. Soft-start will be reinititated after a short-circuit
fault.
W
U
U
Thermal Considerations
Most of the IC power dissipation is derived from the V
IN
pin. The V
IN
current depends on a number of factors
including: oscillator frequency; loads on V5; slew settings;
gate charge current. Additional power is dissipated if V5
sinks current and during the MOSFET gate discharge.
The power dissipation in the IC will be the sum of:
1) The RMS V
IN
current times V
IN
2) V5 RMS sink current times 5V
3) The gate drive’s RMS discharge current times voltage
Because of the strong V
IN
component it is advantageous
to operate the LT1683 at as low a V
IN
as possible.
It is always recommended that package temperature be
measured in each application. The part has an internal
thermal shutdown to minimize the chance of IC destruc-
tion but this should not replace careful thermal design.
The thermal shutdown feature does not protect the exter-
nal MOSFETs. A separate analysis must be done for those
devices to insure that they are operating within safe limits.
Once IC power dissipation, P
DIS
, is determined die junc-
tion temperature is then computed as:
T
J
= T
AMB
+ P
DIS
θ
JA
where T
AMB
is ambient temperature and
θ
JA
is the package
thermal resistance. For the 20-pin SSOP,
θ
JA
is 100
°
C/W.
Magnetics
Design of magnetics is dependent on topology. The fol-
lowing details the design of the magnetics for a push-pull
converter. In this converter the transformer usually stores
little energy. The following equations should be consid-
ered as the starting point to building a prototype.
The following definitions will be used:
V
IN
= Input supply voltage
R
ON
= Switch-on resistance
I
SW
= Maximum switch current
V
OUT
= Desired output voltage
I
OUT
= Output current
f = Oscillator frequency
V
F
= Forward drop of the rectifier
Duty cycle is the major defining equation for this topology.
Note that the output L and C basically filter the chopped
voltage so duty cycle controls output voltage. N is the
turns ratio of the transformer. The turns ratio must be
large enough to ensure that the transformer can put out a
voltage equal to the output voltage plus the diode under
minimum input conditions. Note the transformer operates
at half the oscillator frequency (f).
N
V
V
DC
V
I
R
(
R
OUT
F
MAX
IN MIN
(
SW
ON
SENSE
=
+
(
)
+
)
[
]
2
)
DC
MAX
is the maximum duty cycle of each driver with
respect to the entire cycle, which consists of two periods
(A on and B on). So the effective duty cycle is 2 DC
MAX
.
The controller, in general, determines maximum duty
cycle. A 44% maximum duty cycle is a guaranteed value
for this part.
Remember to add sufficient margin in the turns ratio to
account for IR drops in the transformer windings, worst-
case diode forward drops and switch on voltage. Also at
very slow slew rates the effective DC may be reduced.
There are a number of ways to choose the inductance
value for L. We suggest as a starting point that L be
selected such that the converter is continuous at
I
OUT(MAX)
/4. If your minimum I
OUT
is higher than this or
your components can handle higher peak currents then
use a higher number.
D1
Figure 7. Push-Pull Topology
1:N
L
PRI
D2
L
C
R
OUT
R
SENSE
V
OUT
V
IN
1683 F07
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| LT1683EG | 功能描述:IC REG CTRLR PWM CM 20-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1683EG#PBF | 功能描述:IC REG CTRLR PWM CM 20-SSOP 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 |
| LT1683EG#TR | 功能描述:IC REG CTRLR PWM CM 20-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1683EG#TRPBF | 功能描述:IC REG CTRLR PWM CM 20-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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