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| 型号： | LTC3714EG#TR |
| 厂商： | Linear Technology |
| 文件页数： | 13/28页 |
| 文件大小： | 0K |
| 描述： | IC STP-DWN CNTRLR W/OPAMP 28SSOP |
| 标准包装： | 2,000 |
| 应用： | 控制器，Intel Pentium? |
| 输入电压： | 4 V ~ 36 V |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 1.75 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 28-SSOP |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC3714EGTR |
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LTC3714
APPLICATIONS INFORMATION
2.0
1.5
Tying a resistor R ON from V IN to the I ON pin yields an
on-time inversely proportional to V IN . For a step-down
converter, this results in approximately constant frequency
operation as the input supply varies:
1.0
f =
V OUT
V VON R ON (10pF)
R ON2 =
R ON
0.5
0
– 50 0 50 100 150
JUNCTION TEMPERATURE (°C)
3714 F02
Figure 3. R DS(ON) vs Temperature
The resulting power dissipation in the MOSFETs at maxi-
mum output current are:
P TOP = D TOP I OUT(MAX)2 ρ T(TOP) R DS(ON)(MAX)
+ k V IN2 I OUT(MAX) C RSS f
P BOT = D BOT I OUT(MAX)2 ρ T(BOT) R DS(ON)(MAX)
Both MOSFETs have I 2 R losses and the top MOSFET
includes an additional term for transition losses, which
are largest at high input voltages. The constant k = 1.7A –1
can be used to estimate the amount of transition loss. The
bottom MOSFET losses are greatest when the bottom
duty cycle is near 100%, during a short-circuit or at high
input voltage.
Operating Frequency
The choice of operating frequency is a tradeoff between
efficiency and component size. Low frequency operation
improves efficiency by reducing MOSFET switching losses
but requires larger inductance and/or capacitance in order
to maintain low output ripple voltage.
The operating frequency of LTC3714 applications is de-
termined implicitly by the one-shot timer that controls the
on-time t ON of the top MOSFET switch. The on-time is set
by the current into the I ON pin and the voltage at the V ON
pin according to:
To hold frequency constant during output voltage changes,
tie the V ON pin to V OUT . The V ON pin has internal clamps
that limit its input to the one-shot timer. If the pin is tied
below 0.7V, the input to the one-shot is clamped at 0.7V.
Similarly, if the pin is tied above 2.4V, the input is clamped
at 2.4V.
Because the voltage at the I ON pin is about 0.7V, the current
into this pin is not exactly inversely proportional to V IN ,
especially in applications with lower input voltages. To
correct for this error, an additional resistor R ON2 connected
from the I ON pin to the 5V INTV CC supply will further help
to stabilize the frequency.
5V
0.7V
Changes in the load current magnitude will also cause
frequency shift. Parasitic resistance in the MOSFET
switches and inductor reduce the effective voltage across
the inductance, resulting in increased duty cycle as the
load current increases. By lengthening the on-time slightly
as current increases, constant frequency operation can be
maintained. This is accomplished with a resistive divider
from the I TH pin to the V ON pin and V OUT . The values
required will depend on the parasitic resistances in the
specific application. A good starting point is to feed about
25% of the voltage change at the I TH pin to the V ON pin
as shown in Figure 4a. Place capacitance on the V ON pin
to filter out the I TH variations at the switching frequency.
The resistor load on I TH reduces the DC gain of the error
amp and degrades load regulation, which can be avoided
by using the PNP emitter follower of Figure 4b.
t ON = VON (10pF)
V
I ION
3714f
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| LTC3716EG | 功能描述:IC REG CTRLR BUCK PWM CM 36-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:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3716EG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-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:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3716EG#TR | 功能描述:IC REG CTRLR BUCK PWM CM 36-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 |
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| LTC3717-1#PBF | 制造商:LINEAR 功能描述: 制造商:Linear Technology 功能描述: |
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