参数资料
型号: LTC3869IGN-2#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, PDSO28
封装: 0.150 INCH, LEAD FREE, PLASTIC, SSOP-28
文件页数: 25/40页
文件大小: 2705K
代理商: LTC3869IGN-2#TRPBF
LTC3869/LTC3869-2
31
3869f
For a 2mΩ sense resistor, a short-circuit to ground will
result in a folded back current of:
ISC =
1/ 3
(
)50mV
0.002Ω
1
2
90ns(20V)
0.56H
= 6.7A
A Renesas RJK0330DPB, RDS(ON) = 3.9m, is chosen for
the bottom FET. The resulting power loss is:
PSYNC =
20V – 1.8V
20V
15A
(
)
2
1+ 0.005
(
) 75°C – 25°C
(
)
0.0039Ω
PSYNC = 1W
CIN is chosen for an RMS current rating of at least 7.5A at
temperature assuming only channel 1 or 2 is on. COUT is
chosen with an equivalent ESR of 4.5m for low output
ripple.Theoutputrippleincontinuousmodewillbehighest
at the maximum input voltage. The output voltage ripple
due to ESR is approximately:
VORIPPLE = RESR (IL) = 0.0045 6.8A = 31mVP–P
Further reductions in output voltage ripple can be made
by placing a 100F ceramic across COUT.
APPLICATIONS INFORMATION
For each channel, 0.1F is selected for C1.
R1=
L
(DCRMAX at 25°C) C1
=
0.56H
1.8mΩ 0.1F
= 3.11k
Choose R1 = 3.09k
The power loss in R1 at the maximum input voltage is:
PLOSSR1=
(VIN(MAX) VOUT) VOUT
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 RSENSE 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 VOUT,
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: RDS(ON) = 13m (max), VMILLER =
2.6V, CMILLER 150pF. At maximum input voltage with TJ
(estimated) = 75°C:
PMAIN =
1.8V
20V
15A
(
)
2 1+(0.005)(75°C – 25°C)
[
]
0.013Ω
(
)+ 20V
(
)
2 15A
2
( ) 150pF
(
)
1
5V – 2.6V
+
1
2.6V
400kHz
(
)
= 329mW + 288mW
= 617mW
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