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参数资料
| 型号： | LTC1778EGN |
| 厂商： | Linear Technology |
| 文件页数： | 17/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SSOP |
| 标准包装： | 100 |
| 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： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
LTC1778/LTC1778-1
APPLICATIO S I FOR ATIO
? 1 – ? = 5 . 1 A
(
) (
)
( 1 . 5 ) ( 0 . 010 ? ) ( )
Otherlosses,includingC OUT ESRloss,SchottkydiodeD1
conduction loss during dead time and inductor core loss
generally account for less than 2% additional loss.
When making adjustments to improve efficiency, the
input current is the best indicator of changes in efficiency.
If you make a change and the input current decreases, then
the efficiency has increased. If there is no change in input
current, then there is no change in efficiency.
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V OUT immediately shifts by an amount
equal to ? I LOAD (ESR), where ESR is the effective series
resistance of C OUT . ? I LOAD also begins to charge or
discharge C OUT generating a feedback error signal used by
the regulator to return V OUT to its steady-state value.
During this recovery time, V OUT can be monitored for
overshoot or ringing that would indicate a stability prob-
Selecting a standard value of 1.8 μ H results in a maximum
ripple current of:
2 . 5 V ? 2 . 5 V ?
? I L =
250 kHz 1 . 8 μ H ? 28 V ?
Next, choose the synchronous MOSFET switch. Choosing
a Si4874 (R DS(ON) = 0.0083 ? (NOM) 0.010 ? (MAX),
θ JA = 40 ° C/W) yields a nominal sense voltage of:
V SNS(NOM) = (10A)(1.3)(0.0083 ? ) = 108mV
Tying V RNG to 1.1V will set the current sense voltage range
for a nominal value of 110mV with current limit occurring
at 146mV. To check if the current limit is acceptable,
assume a junction temperature of about 80 ° C above a
70 ° C ambient with ρ 150 ° C = 1.5:
146 mV 1
I LIMIT ≥ + 5 . 1 A = 12 A
2
and double check the assumed T J in the MOSFET:
( ) ( ) . 1 5 ( ) ? = 1 . 97 W
lem. The I TH pin external components shown in Figure 9
will provide adequate compensation for most applica-
tions. For a detailed explanation of switching control loop
P BOT =
28 V – 2 .5V
28 V
2
12 A 0 . 010
( 0 . 7 V )( 250 kHz )( 10 pF )
( ) ( 1 . 4 ) ( 0 . 0165 ? ) +
( )( ) ( )( )( )
theory see Application Note 76.
Design Example
As a design example, take a supply with the following
specifications: V IN = 7V to 28V (15V nominal), V OUT = 2.5V
± 5%, I OUT(MAX) = 10A, f = 250kHz. First, calculate the
timing resistor with V ON = V OUT :
2 . 5 V
R ON = = 1 . 42 M ?
and choose the inductor for about 40% ripple current at
the maximum V IN :
T J = 70 ° C + (1.97W)(40 ° C/W) = 149 ° C
Because the top MOSFET is on for such a short time, an
Si4884 R DS(ON)(MAX) = 0.0165 ? , C RSS = 100pF, θ JA =
40 ° C/W will be sufficient. Checking its power dissipation
at current limit with ρ 100 ° C = 1.4:
2. 5V 2
P TOP = 12 A
28 V
2
1 . 7 28 V 12 A 100 pF 250 kHz
= 0 . 30 W + 0 . 40 W = 0 . 7 W
)( )( )
? 1 ?
? = 2 . 3 μ H
L =
(
2 . 5 V ?
250 kHz 0 . 4 10 A ?
2 . 5 V ?
28 V ?
T J = 70 ° C + (0.7W)(40 ° C/W) = 98 ° C
The junction temperatures will be significantly less at
nominal current, but this analysis shows that careful
attention to heat sinking will be necessary in this circuit.
1778fb
17
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| LTC1778EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC1778EGN#TR | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC1778EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC1778EGN-1 | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC1778EGN-1#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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 |
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