参数资料
型号: LTC4352HDD#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO12
封装: 3 X 3 MM, LEAD FREE, PLASTIC, DFN-12
文件页数: 3/16页
文件大小: 218K
代理商: LTC4352HDD#TRPBF
LTC4352
11
4352fa
SOURCE
LTC4352
TO LOAD
5V
Q1
Si7336ADP
4352 F07
VIN
GATE
OUT
C2
0.1F
R7
1k
GND
12V
CPO
Figure 7. 5V Ideal Diode with External 12V Powering CPO for
Faster Start-up and Refresh
applicaTions inForMaTion
External CPO Supply
The internal charge pump takes milliseconds to charge
up the CPO pin capacitor especially during device power
up. This time can be shortened by connecting an external
supply to the CPO pin. A series resistor is needed to limit
the current into the internal clamp between the CPO and
SOURCE pins. The CPO supply should also be higher than
the main input supply to meet the gate drive requirements
of the MOSFET. Figure 7 shows such a 5V ideal diode ap-
plication, where a 12V supply is connected to the CPO pin
through a 1k resistor. The 1k limits the current into the
CPO pin to 5.3mA, when the SOURCE pin is grounded.
Input Transient Protection
When the capacitances at the input and output are very
small, rapid changes in current can cause transients that
exceed the 24V Absolute Maximum Rating of the VIN and
OUTpins.InORingapplicationsusingasingleMOSFET,one
surge suppressor connected from OUT to ground clamps
all the inputs. In the absence of a surge suppressor, an
outputcapacitanceof10μFissufficientinmostapplications
to prevent the transient from exceeding 24V. Back-to-back
MOSFET applications, depending on voltage levels, may
require a surge suppressor on each supply input.
Design Example
The following design example demonstrates the calcula-
tions involved for selecting components in a 12V system
with 10A maximum load current (see Figure 1).
First, calculate the RDS(ON) of the MOSFET to achieve the
desired forward drop at full load. Assuming a VFWD of
50mV (which is comfortably below the 200mV minimum
open MOSFET fault threshold):
RDS ON
( ) ≤
VFWD
ILOAD
=
50mV
10A
=5m
The Si7336ADP offers a good solution, in a SO-8 sized
package, with a maximum RDS(ON) of 4mΩ and BVDSS of
30V. The maximum power dissipation in the MOSFET is:
P = I2LOAD RDS(ON) = (10A)2 4mΩ = 0.4W
With a maximum steady-state thermal resistance,
θJA,
of 65°C/W, 0.4W causes a modest 26°C rise in junction
temperature of the Si7336ADP above the ambient.
The input capacitance, CISS, of the Si7336ADP is about
6500pF. Slightly exceeding the 10x recommendation, a
0.1F capacitor is selected for C2.
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