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參數(shù)資料
| 型號(hào)： | TPS40077PWPRG4 |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 2 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | GREEN, PLASTIC, HTSSOP-16 |
| 文件頁(yè)數(shù)： | 22/43頁(yè) |
| 文件大小： | 847K |
| 代理商： | TPS40077PWPRG4 |
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t
START w 2p
LOUT
COUT
(36)
C
SS +
I
SS
V
FB
t
START
(37)
I
SCP w
COUT
V
OUT
t
START
) IPK
(38)
R
ILIM +
I
SCP
R
DS(on)MAX ) VILIM(Max)
I
LIM(Min)
(39)
I
SCP(MIN) +
I
ILIM(MIN)
R
ILIM(MIN) * VILIM(MAX)
R
DS(on)MAX
(40)
I
SCP(MAX) +
I
ILIM(MAX)
R
ILIM(MAX) * VILIM(MIN)
R
DS(on)MIN
(41)
C
ILIM(Max) +
V
OUT
0.2
V
IN
R
ILIM
f
S
(42)
www.ti.com ..................................................................................................................................................... SLUS714D – JANUARY 2007 – REVISED APRIL 2009
Soft-Start Capacitor, CSS
It is good practice to limit the rise time of the output voltage. This helps prevent output overshoot and possible
damage to the load. The selection of the soft-start time is arbitrary. It must meet one condition: it should be
greater than the time constant of the output filter, LOUT and COUT. This time is given by
The soft-start time must be greater than 0.23 ms. A time of 0.75 ms was chosen. This time also helps limit the
initial input current during start-up so that the peak current plus the capacitor start-up current is less than the
minimum short-circuit current. The value of CSS can be calculated using Equation 37.
A standard 15-nF MLCC capacitor was chosen. The calculated start time using this capacitor is 0.875 ms.
Short-Circuit Protection, RILIM and CILIM
Short-circuit protection is programmed using the RILIM resistor. Selection of this resistor depends on the RDS(on) of
the switching MOSFET selected and the required short-circuit current trip point, ISCP. The minimum ISCP is limited
by the inductor peak current, the output voltage, the output capacitor, and the soft-start time. Their relationship is
given by Equation 38. A short-circuit current trip point greater than that calculated by this equation should be
used.
The minimum short-circuit current trip point for this design is 12.25 A. This value is used in Equation 39 to
calculate the minimum RILIM value.
RILIM is calculated to be 1.17 k, and a 1.2-k resistor is used to verify that the short-circuit current requirements
are met. The minimum and maximum short-circuit current can be calculated using Equation 40 and Equation 41.
where: VILIM(MAX) and VILIM(MIN) are maximum and minimum voltages across the high side FET when it is turned
on, taking into account temperature variations.
The minimum ISCP is 12.25 A, and the maximum is 34 A.
It is also recommended to add a small capacitor, CILIM, across RILIM. The value of this capacitor should be about
half the value calculated in Equation 42.
This equation yields a maximum CILIM as 55 pF. A smaller value of 27 pF is chosen is chosen.
Boost Voltage, CBOOST and DBOOST (Optional)
To be able to drive an N-channel MOSFET in the switch location of a buck converter, a capacitor charge pump
or boost circuit is required. The TPS40077 contains the elements for this boost circuit. The designer must only
add a capacitor, CBOOST, from the switch node of the buck power stage to the BOOST pin of the IC. Selection
of this capacitor is based on the total gate charge of the switching MOSFET and the allowable ripple on the
boost voltage,
ΔVBOOST. A ripple of 0.2 V is assumed for this design. Using these two parameters and
Equation 43, the minimum value for CBOOST can be calculated.
Copyright 2007–2009, Texas Instruments Incorporated
29
Product Folder Link(s) :TPS40077
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| TPS40090 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:HIGH FREQUENCY MULTIPHASE CONTROLLER |
| TPS40090EVM-001 | 功能描述:電源管理IC開(kāi)發(fā)工具 TPS40090-001 Eval Mod RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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