参数资料
型号: TPS2391DGKRG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8
封装: GREEN, PLASTIC, MSOP-8
文件页数: 6/20页
文件大小: 497K
代理商: TPS2391DGKRG4
TPS2390
TPS2391
SLUS471D JUNE 2002 REVISED JANUARY 2008
14
www.ti.com
APPLICATION INFORMATION
setting the fault timing capacitor
The fault timeout period is established by the value of the capacitor connected to the FLTTIME pin, CFLT. The
timeout period permits riding out spurious current glitches and surges that may occur during operation of the
system, and prevents indefinite sourcing into faulted loads swapped into a live system. However, to ensure
smooth voltage ramping under all conditions of load capacitance and input supply potential, the minimum
timeout should be set to accommodate these system variables. To do this, a rough estimate of the maximum
voltage ramp time for a completely discharged plug-in card provides a good basis for setting the minimum timer
delay.
Due to the three-phase nature of the load current at turn-on, the load voltage ramp potentially has three distinct
phases ( compare Figures 1 and 2). This profile depends on the relative values of load capacitance, input dc
potential, maximum current limit and other factors. The first two phases are characterized by the two different
slopes of the current ramp; the third phase, if required for bulk capacitance charging, is the constant-current
charging at IMAX. Considering the two current ramp phases to be one period at an average di/dt simplifies
calculation of the required timing capacitor.
For the TPS2390 and TPS2391, the typical duration of the soft-start ramp period, tSS, is given by equation (3).
t
SS + 1183
C
IRAMP
where:
t
SS is the soft-start period in ms, and
C
IRAMP is given in F
During this current ramp period, the load voltage magnitude which is attained is estimated by equation (4).
V
LSS +
i
AVG
2
C
L
C
IRAMP
100
R
SENSE
t
SS
2
where:
V
LSS is the load voltage reached during soft-start,
i
AVG is 3.38 A for the TPS2390 and TPS2391,
C
L is the amount of the load capacitance, and
t
SS is the soft-start period, in seconds
The quantity iAVG in equation (4) is a weighted average of the two charge currents applied to CIRAMP during
turn-on, considering the typical output values.
(3)
(4)
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