参数资料
型号: LTC3866EFE#TRPBF
厂商: Linear Technology
文件页数: 29/36页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 24TSSOP
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 850kHz
占空比: 95%
电源电压: 4.5 V ~ 38 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 24-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
LTC3866
APPLICATIONS INFORMATION
V OUT ? V OUT ?
f ? L ? ?
V IN(NOM) ? ?
t ON(MIN) =
V OUT 1.5V
= = 187ns
( 30A ) 2 [ 1 + (0.005)(75 ° C – 25 ° C) ] ?
P MAIN =
( 0.0071 ? ) + ( 20V ) 2 ?
? ( 2 ? ) ( 35pF ) ?
? ? 5.5V – 2.8V + 2.8V ? ? ( 400kHz )
Thisdesignwillrequire0.33μH.TheWürth744301033,
0.32μH inductor is chosen. At the nominal input voltage
(12V), the ripple current will be:
? I L(NOM) = ? 1 ? ?
It will have 10A (33%) ripple. The peak inductor current
will be the maximum DC value plus one-half the ripple
current, or 35A.
The minimum on-time occurs at the maximum V IN , and
should not be less than 90ns:
V IN(MAX) f 20V(400kHz)
MOSFET results in: R DS(ON) = 7.1m? (max), V MILLER =
2.8V, C MILLER ? 35pF. At maximum input voltage with T J
(estimated) = 75°C:
1.5V
20V
? 30A ?
? 2 ?
? 1 1 ?
= 599mW + 122mW
= 721mW
For a 0.32mΩ DCR, a short-circuit to ground will result
in a folded back current of:
DCR sensing is used in this circuit. If C1 and C2 are chosen
to be 220nF, based on the chosen 0.33μH inductor with
0.32mΩ DCR, R1 and R2 can be calculated as:
I SC =
? ?
( 1/ 3 ) 15mV – 1 ? 90ns(20V) ? = 12.9A
0.0032 ? 2 ? 0.33μH ?
R1 =
L
DCR ? C1
= 4.69k
An Infineon BSC010NE2LS, R DS(ON) = 1.1m?, is chosen
for the bottom FET. The resulting power loss is:
R2 =
= 937 ?
( 30A ) 2 ?
P SYNC =
L
DCR ? C2 ? 5
Choose R1 = 4.64k and R2 = 931Ω.
The maximum DCR of the inductor is 0.34Ω. The
V SENSE(MAX) is calculated as:
V SENSE(MAX) = I PEAK ? DCR MAX = 12mV
The current limit is chosen to be 15mV. If temperature
variation is considered, please refer to Inductor DCR
Sensing Temperature Compensation with NTC Thermistor.
The power dissipation on the topside MOSFET can be
easily estimated. Choosing an Infineon BSC050NE2LS
20V – 1.5V
20V
?? 1 + ( 0.005 ) ? ( 75 ° C – 25 ° C ) ?? ? 0.0011 ?
P SYNC = 1.14W
C IN is chosen for an equivalent RMS current rating of at
least 13.7A. C OUT is chosen with an equivalent ESR of
4.5m? for low output ripple. The output ripple in continu-
ous mode will be highest at the maximum input voltage.
The output voltage ripple due to ESR is approximately:
V ORIPPLE = R ESR (?I L ) = 0.0045? ? 10 A = 45mV P-P
Further reductions in output voltage ripple can be made
by placing a 100μF ceramic capacitor across C OUT .
3866fb
29
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