參數(shù)資料
型號(hào): TPS40051PWPR
廠(chǎng)商: TEXAS INSTRUMENTS INC
元件分類(lèi): 穩(wěn)壓器
英文描述: 0.2 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封裝: GREEN, PLASTIC, HTSSOP-16
文件頁(yè)數(shù): 5/36頁(yè)
文件大?。?/td> 648K
代理商: TPS40051PWPR
TPS40050
TPS40051
TPS40053
SLUS540F DECEMBER 2002 REVISED JUNE 2004
www.ti.com
13
APPLICATION INFORMATION
Energy in the capacitor is described in equation (10).
E
C +
1
2
C
V2 (Joules)
where:
V2
+ V
f
2
* V
i
2
Volts2
where:
D Vf is the final peak capacitor voltage
D Vi is the initial capacitor voltage
Substituting equation (9) into equation (8), then substituting equation (11) into equation (10), then setting
equation (10) equal to equation (8), and then solving for CO yields the capacitance described in equation (12).
C
O +
L
I
OH
2
* I
OL
2
V
f
2
* V
i
2
(Farads)
PROGRAMMING SOFT START
TPS4005x uses a closed-loop approach to ensure a controlled ramp on the output during start-up. Soft-start
is programmed by charging an external capacitor (CSS) via an internally generated current source. The voltage
on CSS is fed into a separate non-inverting input to the error amplifier (in addition to FB and 0.7-V VREF). The
loop is closed on the lower of the CSS voltage or the internal reference voltage ( 0.7-V VREF). Once the CSS
voltage rises above the internal reference voltage, regulation is based on the internal reference. To ensure a
controlled ramp-up of the output voltage the soft-start time should be greater than the L-CO time constant as
described in equation (13).
t
START w 2p
L
C
O
(seconds)
There is a direct correlation between tSTART and the input current required during start-up. The faster tSTART,
the higher the input current required during start-up. This relationship is describe in more detail in the section
titled, Programming the Current Limit which follows. The soft-start capacitance, CSS, is described in
equation (14).
For applications in which the VIN supply ramps up slowly, (typically between 50 ms and 100 ms) it may be
necessary to increase the soft-start time to between approximately 2 ms and 5 ms to prevent nuisance UVLO
tripping. The soft-start time should be longer than the time that the VIN supply transitions between 6 V and 7 V.
C
SS +
2.3
mA
0.7 V
t
START
(Farads)
(10)
(11)
(12)
(13)
(14)
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