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参数资料
| 型号： | LTC3851AEGN#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PDSO16 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-16 |
| 文件页数： | 17/30页 |
| 文件大小： | 430K |
| 代理商： | LTC3851AEGN#TRPBF |
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LTC3851A
24
3851afa
Design Example
As a design example, assume VIN = 12V (nominal), VIN =
22V (maximum), VOUT = 1.8V, IMAX = 5A, and f = 250kHz.
Refer to Figure 13.
The inductance value is chosen first based on a 30%
ripple current assumption. The highest value of ripple
current occurs at the maximum input voltage. Connect a
160k resistor between the FREQ/PLLFLTR and GND pins,
generating 250kHz operation. The minimum inductance
for 30% ripple current is:
ΔIL =
1
f
( ) L()
VOUT 1
VOUT
VIN
A 4.7H inductor will produce 28% ripple current and a
3.3H will result in 40%. The peak inductor current will be
the maximum DC value plus one-half the ripple current, or
6A, for the 3.3H value. Increasing the ripple current will
also help ensure that the minimum on-time of 90ns is not
violated. The minimum on-time occurs at maximum VIN:
tON(MIN) =
VOUT
VIN(MAX) f
( )
=
1.8V
22V 250kHz
(
)
= 327ns
The RSENSE resistor value can be calculated by connect-
ing ILIM to INTVCC and using the maximum current sense
voltage specification with some accommodation for toler-
ances. Tie ILIM to INTVCC.
RSENSE ≤
75mV
6A
= 0.0125Ω, so 0.01Ω is selected
Choosing 1% resistors: R1 = 25.5k and R2 = 32.4k yields
an output voltage of 1.816V.
applicaTions inForMaTion
ThepowerdissipationonthetopsideMOSFETcanbeeasily
estimated. Choosing a Fairchild FDS6982S dual MOSFET
results in: RDS(ON) = 0.035/0.022, CMILLER = 215pF. At
maximum input voltage with T (estimated) = 50°C:
PMAIN =
1.8V
22V
5
( )2 1+ 0.005
(
) 50°C25°C
(
)
0.035
Ω
(
)+ 22V
( )2
5A
2
2Ω
( ) 215pF
(
)
1
5
2.3
+
1
2.3
250kHz
(
) = 185mW
A short circuit to ground will result in a folded back cur-
rent of:
ISC =
29mV
0.0125
Ω
– 1
2
90ns 22V
( )
3.3H
= 2.02A
with a typical value of RDS(ON) and δ = (0.005/°C)(25°C)
= 0.125. The resulting power dissipated in the bottom
MOSFET is:
PSYNC =
22V
2.02A
(
)2 1.125
(
) 0.022Ω
(
)
= 101.0mW
which is less than under full-load conditions.
CIN is chosen for an RMS current rating of at least 3A at
temperature. COUT is chosen with an ESR of 0.02 for
low output ripple. The output ripple in continuous mode
will be highest at the maximum input voltage. The output
voltage ripple due to ESR is approximately:
VORIPPLE = RESR (IL) = 0.02 (2A) = 40mVP-P
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| LTC3851AEMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP 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) |
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