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参数资料
| 型号： | LTC3778EF#TR |
| 厂商： | Linear Technology |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 20TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 电源电压： | 4 V ~ 36 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 ~ 85°C |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC3778EFTR |
LTC3778
APPLICATIO S I FOR ATIO
The ρ T term is a normalization factor (unity at 25 ° C)
accounting for the significant variation in on-resistance
with temperature, typically about 0.4%/ ° C as shown in
Figure 2. For a maximum junction temperature of 100 ° C,
using a value ρ T = 1.3 is reasonable.
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.
2.0
The operating frequency of LTC3778 applications is deter-
1.5
1.0
mined 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:
t ON =
V VON
0.5
0
– 50
0 50 100
JUNCTION TEMPERATURE ( ° C)
150
( 10 pF )
I ION
Tying a resistor R ON from V IN to the I ON pin yields an on-
3778 F02
Figure 2. R DS(ON) vs. Temperature
time inversely proportional to V IN . For a step-down con-
verter, this results in approximately constant frequency
operation as the input supply varies:
The power dissipated by the top and bottom MOSFETs
strongly depends upon their respective duty cycles and
the load current. When the LTC3778 is operating in
f =
V OUT
( V VON ) R ON ( 10 pF )
[ Hz ]
D TOP =
= IN OUT
R ON 2 =
continuous mode, the duty cycles for the MOSFETs are:
V OUT
V IN
V – V
D BOT
V IN
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.
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. If output is above 2.4V, use a resistive divider from
V OUT to V ON pin.
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 stabilize the frequency.
5 V
R ON
0 . 7 V
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
3778f
11
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| LTC3780EG#PBF | 功能描述:IC REG CTRLR BST PWM CM 24-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 |
| LTC3780EG#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Synchronous Boost/Buck Controller 4V to 36V Input 24-Pin SSOP T/R |
| LTC3780EG#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 24-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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