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參數(shù)資料
| 型號： | TPS40055EVM |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | TPS40055 EVALUATION MODULE(TPS40055評估模塊) |
| 中文描述： | TPS40055評估模塊（TPS40055評估模塊） |
| 文件頁數(shù)： | 7/18頁 |
| 文件大小： | 350K |
| 代理商： | TPS40055EVM |
SLUU190 April 2004
7
Wide Range Input TPS40055 Converter Delivers 5 Volts at 2 Amps
4.3
UVLO circuitry
The user programmable UVLO built into the TPS4005X provides hysteresis for transients shorter than a total
count of seven cycles. If the input voltage to the converter can be slowly rising around the minimum V
IN
range,
external hysteresis can be incorporated to prevent multiple on/off cycles during startup or shutdown. These
on/off cycles are a result of line impedance external to the EVM causing V
IN
to the module to drop when under
load, causing the programmable UVLO threshold to be crossed repetitively.
In this converter, C16 and D2 are added to form a peak detector from the lower gate drive which is only active
when the converter is operating. This provides a bias source to deliver hysteresis current from the peak detector
voltage through R12 to the lower KFF voltage of 3.5 V, enabling one to alter the programmable UVLO shutdown
point. The bias is not present during startup, so the circuit starts as expected from the R
KFF
calculation.
In this application, R12 is selected to provide a hysteresis current of 20% I
KFF
and can be calculated from
R
HYS
R12
R
KFF
0.2
V
PD
3.5
V
IN(min)
3.5
where V
PD
is the voltage on the peak detector, and V
IN(min)
is the desired start voltage used in the determination
of R
KFF
. In our typical case, V
PD
= 8 V, and R12 is found to be 247 k
, and a standard value of 243 k
is selected.
Testing shows the startup voltage to be 9.2 V, and the shutdown voltage to be 8.5 V.
4.4
Inductance value
The output inductor value for a buck converter can be selected from equation (4).
L
V
OUT
I
RIPPLE
f
1
V
OUT
V
IN(min)
in which I
RIPPLE
is usually chosen to be in the range of 10% to 40% of I
OUT
. With I
RIPPLE
= 20% of I
OUT(max)
there
is a ripple current of 0.6 A, and the inductance value is found to be 24
μ
H for a maximum V
IN
of 40 V. In a wide
range V
IN
design the inductor value selection involves a lot of compromise. This design specifically targets the
higher voltage range of operation attainable with the TPS40055 controller, so a standard value 22-
μ
H inductor
is selected. With a 22-
μ
H inductor, the ripple current with V
IN
= 10 V is 0.38 A, and the ripple with V
IN
= 40 V
is 0.66 A. Using the larger inductor at lower voltages helps to reduce the number of output capacitors required
to meet the output noise specification, as discussed in a later section. If the input range was constrained to a
lower voltage range such as 10 V to 16 V a smaller inductor would be selected.
A ferrite drum core with a surface mount carrier provides a low-cost solution inductors in this inductance/current
range. Inductors rated 22
μ
H are available in a couple of sizes, with the larger versions generally rated to carry
higher saturation current, which is the current for 30% inductor value rolloff. In this example an inductor with a
inch diameter drum core is selected because the saturation current is rated 7.6 A. The next physically smaller
inductor has a saturation rating of 3.7 A, and does not allow sufficient margin for the tolerances in the current
limit circuitry.
(3)
(4)
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| TPS40055EVM-001 | 功能描述:電源管理IC開發(fā)工具 Eval Mod Converter RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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| TPS40055MPWPREPG4 | 功能描述:DC/DC 開關(guān)控制器 Synch Buck Cntrlr, source/sink RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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