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參數(shù)資料
| 型號： | DS1244Y |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | Timer or RTC |
| 英文描述： | 0 TIMER(S), REAL TIME CLOCK, PDIP28 |
| 封裝： | 0.740 INCH, PLASTIC, DIP-28 |
| 文件頁數(shù)： | 9/21頁 |
| 文件大?。?/td> | 1965K |
| 代理商： | DS1244Y |
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
17
when LIR is higher than 2.0, and it works in CCM mode
when LIR is lower than 2.0. The best trade-off between
inductor size and converter efficiency for step-up regula-
tors generally has an LIR between 0.3 and 0.5. However,
depending on the AC characteristics of the inductor core
material and ratio of inductor resistance to other power-
path resistances, the best LIR can shift up or down. If the
inductor resistance is relatively high, more ripples can
be accepted to reduce the number of required turns and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can reduce losses throughout the power path. If
extremely thin high-resistance inductors are used, as is
common for LCD panel applications, an LIR higher than
2.0 can be chosen for DCM operating mode.
Once a physical inductor is chosen, higher and lower
values of the inductor should be evaluated for efficiency
improvements in typical operating regions. The detailed
design procedure for CCM can be described as:
Calculate the approximate inductor value using the
typical input voltage (VIN), the maximum output cur-
rent (IOUT(MAX)), the expected efficiency (ETYP) taken
from an appropriate curve in the Typical Operating
Characteristics, and an estimate of LIR based on the
above discussion:
OUT(MAX)
OUT
IN(DC,MAX)
IN(MIN)
MIN
I
V
I
V
×
=
× η
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input current
at the minimum input voltage VIN(MIN), using conserva-
tion of energy and the expected efficiency at that operat-
ing point (EMIN) taken from an appropriate curve in the
Typical Operating Characteristics:
Calculate the ripple current at that operating point and
the peak current required for the inductor:
(
)
IN(MIN)
OUT(MAX)
IN(MIN)
RIPPLE
CCM
OUT(MAX)
SW
V
I
L
V
f
×
=
×
RIPPLE
PEAK_CCM
IN(DC,MAX)
I
2
=
+
When DCM operating mode is chosen to minimize the
inductor value, the calculations are different from those
above in CCM mode. The maximum inductor value for
DCM mode (or the minimum inductor value for CCM
mode) is calculated with the following equation:
IN(MIN)
DCM(MAX)
OUT(MAX)
2
IN(MIN)
SW
OUT(MAX)
V
L
1
V
2 f
V
I
=
×
× η
×
The peak inductor current in DCM is calculated with the
following equation:
(
)
OUT(MAX)
IN(MIN)
PEAK_DCM
DCM
SW
I
2
V
I
L
f
× ×
=
×
× η
The inductor’s saturation current rating should exceed
IPEAK and the inductor’s DC current rating should
exceed IIN(DC,MAX). For good efficiency, choose an
inductor with less than 0.1I series resistance.
Considering the circuit with six 10-LED strings and
20mA LED full-scale current, the maximum load current
(IOUT(MAX)) is 120mA with a 32V output and a minimal
input voltage of 7V.
Choosing a CCM operating mode with LIR = 0.8 at 1MHz
and estimating efficiency of 85% at this operating point:
2
CCM
7V
32V 7V
0.85
L
10.59 H
32V
120mA 1MHz
0.8
=
×
A 10FH inductor is chosen and the peak inductor current
at minimum input voltage is calculated as follows:
(
)
PEAK_CCM
7V
32V 7V
120mA 32V
I
7V 0.85
2 10 H 32V 1MHz
0.92A
×
×
=
+
×
× ×
×
=
Alternatively, choose a DCM operating mode by using
lower inductance and estimating efficiency of 85% at this
operating point. Since DCM has higher peak inductor
current at lower input, it causes current limit when the
parameters are not chosen properly. Considering the
case with six 10-LED strings and 20mA LED full-scale
current to prevent excessive switch current from causing
current limit:
2
DCM(MAX)
7V
(7V)
0.85
L
1
32V
2 1MHz 32V 120mA
4.24 H
×
=
×
×
=
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| DS1245AB-100 | 128K X 8 NON-VOLATILE SRAM MODULE, 100 ns, DMA32 |
| DS1245Y-120 | 128K X 8 NON-VOLATILE SRAM MODULE, 120 ns, DMA32 |
| DS1245AB-85 | 128K X 8 NON-VOLATILE SRAM MODULE, 85 ns, DMA32 |
| DS1245Y-85 | 128K X 8 NON-VOLATILE SRAM MODULE, 85 ns, DMA32 |
| DS1245Y-70 | 128K X 8 NON-VOLATILE SRAM MODULE, 70 ns, DMA32 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| DS1244Y120 | 制造商:Maxim Integrated Products 功能描述: |
| DS1244Y-120 | 制造商:Maxim Integrated Products 功能描述: |
| DS1244Y-150 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| DS1244Y-200 | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:256K NV SRAM with Phantom Clock |
| DS1244Y-70 | 功能描述:實(shí)時(shí)時(shí)鐘 RoHS:否 制造商:Microchip Technology 功能:Clock, Calendar. Alarm RTC 總線接口:I2C 日期格式:DW:DM:M:Y 時(shí)間格式:HH:MM:SS RTC 存儲容量:64 B 電源電壓-最大:5.5 V 電源電壓-最小:1.8 V 最大工作溫度:+ 85 C 最小工作溫度: 安裝風(fēng)格:Through Hole 封裝 / 箱體:PDIP-8 封裝:Tube |
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