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參數(shù)資料
| 型號(hào)： | LTC1147CS8-3.3 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | SWITCHING CONTROLLER, 400 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大小： | 204K |
| 代理商： | LTC1147CS8-3.3 |
12
LTC1147-3.3
LTC1147-5/LTC 1147L
APPLICATIU
W
U
U
f
MIN
=
3.3
4.5
)
)
1 –
1
2.61
μ
s
= 102kHz
P
P
= 3.3(0.125
)(1A)
2
(1.27)
4.5
= 116mW
This last step is necessary to assure that the power
dissipation and junction temperature of the P-channel are
not exceeded.
Troubleshooting Hints
Since efficiency is critical to LTC1147 series applications,
it is very important to verify that the circuit is functioning
correctly in both continuous and Burst Mode
operation.
The waveform to monitor is the voltage on the timing
capacitor Pin 2.
In continuous mode (I
LOAD
> I
BURST
) the voltage on the C
T
pin should be a sawtooth with a 0.9V
P-P
swing. This
voltage should never dip below 2V as shown in Figure 6a.
When load currents are low (I
LOAD
< I
BURST
) Burst Mode
operation occurs. The voltage on the C
T
pin now falls to
ground for periods of time as shown in Figure 6b. During
this time the LTC1147 series are in sleep mode with the
quiescent current reduced to 160
μ
A.
The inductor current should also be monitored. Look to
verify that the peak-to-peak ripple current in continuous
mode operation is approximately the same as in Burst
Mode
operation.
Other losses including C
IN
and C
OUT
ESR dissipative
losses, MOSFET switching losses, and inductor core losses,
generally account for less than 2% total additional loss.
Design Example
As a design example, assume V
IN
= 5V (nominal), V
OUT
=
3.3V, I
MAX
= 1A, and f = 130kHz; R
SENSE
, C
T
and L can
immediately be calculated:
R
SENSE
= 100mV/1A = 0.1
t
OFF
= (1/130kHz)[1 – (3.3/5)] = 2.61
μ
s
C
T
= 2.61
μ
s/(1.3)(10
4
) = 220pF
L = (5.1)(10
5
)(0.1
)(220pF)(3.3V) = 33
μ
H
Assume that the MOSFET dissipation is to be limited to
P
P
= 250mW.
If T
A
= 50
°
C and the thermal resistance of the MOSFET is
50
°
C/W, then the junction temperatures will be 63
°
C and
δ
P
= 0.007(63 – 25) = 0.27. The required R
DS(ON)
for the
MOSFET can now be calculated:
P-Ch R
DS(ON)
=
5(0.25)
3.3(1)
2
(1.27)= 0.3
The P-channel requirement can be met by a Si9430DY.
Note that the most stringent requirement for the Schottky
diode is with V
OUT
= 0 (i.e., short circuit). During a
continuous short circuit, the worst-case Schottky diode
dissipation rises to:
P
D
= I
SC(AVG)
(V
D
)
With the 0.1
sense resistor I
SC(AVG)
= 1A will result,
increasing the 0.4V Schottky diode dissipation to 0.4W.
C
IN
will require an RMS current rating of at least 0.5A at
temperature, and C
OUT
will require an ESR of 0.1
for
optimum efficiency.
Now allow V
IN
to drop to its minimum value. At lower input
voltages the operating frequency will decrease and the
P-channel will be conducting most of the time, causing the
power dissipation to increase. At V
IN(MIN)
= 4.5V, the
frequency will decrease and the P-channel will be con-
ducting most of the time causing its power dissipation to
increase. At V
IN(MIN)
= 4.5V:
If Pin 2 is observed falling to ground at high output
currents, it indicates poor decoupling or improper ground-
ing. Refer to the Board Layout Checklist.
3.3V
0V
LTC1147 F06
Figure 6b. Burst Mode Operation C
T
Waveform
3.3V
0V
Figure 6a. Continuous Mode Operation C
T
Waveform
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| LTC1147CS8-5 | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC1147CS8-5#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,000 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:50% 電源電壓:9 V ~ 10 V 降壓:無 升壓:是 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:8-TSSOP（0.173"，4.40mm 寬） 包裝:帶卷 (TR) |
| LTC1147CS8-5#TR | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC1147CS8-5#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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