参数资料
型号: LTC3869EUFD#PBF
厂商: Linear Technology
文件页数: 32/42页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 28-QFN
标准包装: 73
系列: PolyPhase®
PWM 型: 电流模式
输出数: 2
频率 - 最大: 850kHz
占空比: 95%
电源电压: 4 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: 28-WFQFN 裸露焊盘
包装: 管件
LTC3869/LTC3869-2
APPLICATIONS INFORMATION
R1 =
L 0.56μH
(DCR MAX
at 25 ° C) ? C1 1.8m Ω ? 0.1μF
Foreachchannel,0.1μFisselectedforC1.
=
Choose R1 = 3.09k
= 3.11k
For a 2mΩ sense resistor, a short-circuit to ground will
result in a folded back current of:
? ?
I SC = ( 1/ 3 ) 50mV – 1 ? 90ns(20V) ? = 6.7A
0.002 Ω 2 ? 0.56μH ?
(V IN(MAX) ? V OUT ) ? V OUT
P LOSS R1 =
( ) 2 ?
P SYNC =
15A
( 15A ) 2 [ 1 + (0.005)(75 ° C – 25 ° C) ] ?
P MAIN =
ThepowerlossinR1atthemaximuminputvoltageis:
R1
The resulting power loss for R1 is 11mW for channel 1
and 7mW for channel 2.
The sum of the sense resistor and DCR is 2.5mΩ (max)
for the R SENSE application whereas the inductor DCR for
the DCR sense application is 1.8mΩ (max). As a result
of the lower conduction losses from the switch node to
V OUT , the DCR sensing application has higher efficiency.
The power dissipation on the topside MOSFET can be
easily estimated. Choosing a Renesas RJK0305DPB
MOSFET results in: R DS(ON) = 13m? (max), V MILLER =
2.6V, C MILLER ? 150pF. At maximum input voltage with
T J (estimated) = 75°C:
1.8V
20V
A Renesas RJK0330DPB, R DS(ON) = 3.9m?, is chosen for
the bottom FET. The resulting power loss is:
20V – 1.8V
20V
?? 1 + ( 0.005 ) ? ( 75 ° C – 25 ° C ) ?? ? 0.0039 Ω
P SYNC = 1W
C IN is chosen for an RMS current rating of at least 7.5A at
temperature assuming only channel 1 or 2 is on. C OUT is
chosen with an equivalent ESR of 4.5m? 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:
V ORIPPLE = R ESR (?I L ) = 0.0045? ? 6.8 A = 31mV P–P
Further reductions in output voltage ripple can be made
by placing a 100μF ceramic across C OUT .
( 0.013 Ω ) + ( 20V ) 2 ?
? ( 2 Ω ) ( 150pF ) ?
? ? 5V – 2.6V + 2.6V ? ? ( 400kHz )
? 15A ?
? 2 ?
? 1 1 ?
= 329mW + 288mW
= 617mW
38692fa
32
For more information www.linear.com/LTC3869
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