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参数资料
| 型号： | TPS61085DGKT |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 2 A SWITCHING REGULATOR, 1500 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | GREEN, PLASTIC, MSOP-8 |
| 文件页数： | 25/25页 |
| 文件大小： | 781K |
| 代理商： | TPS61085DGKT |
Design Procedure
1. Duty Cycle:
1
IN
S
V
D
V
h
=
-
2. Maximum output current:
(
)
1
2
L
swpeak
I
Iout
I
D
D
=
-
-
÷
è
3. Peak switch current:
D
I
out
L
swpeak
-
+
D
=
1
2
with
IN
L
V
D
I
fs L
D
=
Soft-start
Inductor Selection
www.ti.com ...................................................................................................................................................................................................... SLVS859 – JUNE 2008
The first step in the design procedure is to verify that the maximum possible output current of the boost converter
supports the specific application requirements. A simple approach is to estimate the converter efficiency, by
taking the efficiency numbers from the provided efficiency curves or to use a worst case assumption for the
expected efficiency, e.g. 90%.
and
Iswpeak = converter switch current (minimum switch current limit = 2.0 A)
fs = Converter switching frequency (typically 1.2 MHz)
L = Selected inductor value
η = Estimated converter efficiency (please use the number from the efficiency plots or 90% as an estimation)
ΔIL = Inductor peak-to-peak ripple current
The peak switch current is the steady state peak switch current that the integrated switch, inductor and external
Schottky diode has to be able to handle. The calculation must be done for the minimum input voltage where the
peak switch current is the highest.
The boost converter has an adjustable soft-start to prevent high inrush current during start-up. To minimize the
inrush current during start-up an external capacitor connected to the soft-start pin SS is used to slowly ramp up
the internal current limit of the boost converter when charged with a constant current. When the EN pin is pulled
high, the soft-start capacitor CSS) is immediately charged to 0.3 V. The capacitor is then charged at a constant
current of 10
A typically until the output of the boost converter V
S has reached its Power Good threshold (90%
of VS nominal value). During this time, the SS voltage directly controls the peak inductor current, starting with 0 A
at VSS = 0.3 V up to the full current limit at VSS ≈ 800 mV. The maximum load current is available after the
soft-start is completed. The larger the capacitor the slower the ramp of the current limit and the longer the
soft-start time. A 100 nF capacitor is usually sufficient for most of the applications. When the EN pin is pulled
low, the soft-start capacitor is discharged to ground.
The TPS61085 is designed to work with a wide range of inductors. The main parameter for the inductor selection
is the saturation current of the inductor which should be higher than the peak switch current as calculated in the
Design Procedure section with additional margin to cover for heavy load transients. An alternative, more
conservative, is to choose an inductor with a saturation current at least as high as the maximum switch current
limit of 3.2 A. The other important parameter is the inductor dc resistance. Usually, the lower the dc resistance
the higher the efficiency. It is important to note that the inductor dc resistance is not the only parameter
determining the efficiency. Especially for a boost converter where the inductor is the energy storage element, the
type and core material of the inductor influences the efficiency as well. At high switching frequencies of 1.2 MHz
inductor core losses, proximity effects and skin effects become more important. Usually, an inductor with a larger
form factor gives higher efficiency. The efficiency difference between different inductors can vary between 2% to
10%. For the TPS61085, inductor values between 3
H and 6 H are a good choice with a switching frequency
of 1.2 MHz, typically 3.3
H. At 650 kHz we recommend inductors between 6 H and 13 H, typically 6.8 H.
Possible inductors are shown in Table 1.
Copyright 2008, Texas Instruments Incorporated
9
Product Folder Link(s): TPS61085
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| TPS61085PWG4 | 功能描述:直流/直流开关调节器 650kHz 1.2MHz Step- Up DC-DC Cnvrtr RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| TPS61085PWR | 功能描述:直流/直流开关调节器 650kHz 1.2MHz Step- Up DC-DC Converter RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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