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參數(shù)資料
| 型號(hào)： | MAX1791EUB |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High-Efficiency, 10-Pin レMAX, Step-Down Controllers for Notebooks |
| 中文描述： | SWITCHING CONTROLLER, 328 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | MICRO MAX PACKAGE-10 |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 391K |
| 代理商： | MAX1791EUB |
M
High-Efficiency, 10-Pin μMAX, Step-Down
Controllers for Notebooks
14
______________________________________________________________________________________
then the PWM is latched off and will not restart until VP
power is cycled, or
SHDN
is toggled low then high.
Design Procedure
Begin by establishing the input voltage range and max-
imum load current before choosing an inductor and its
associated ripple-current ratio (LIR). The following four
factors dictate the rest of the design:
1)
Input voltage range.
The maximum value (V
VP
(MAX)
) must accommodate the maximum AC
adapter voltage. The minimum value (V
VP(MIN)
)
must account for the lowest input voltage after
drops due to connectors, fuses, and battery selec-
tor switches. If there is a choice at all, lower input
voltages result in better efficiency.
2)
Maximum load current.
There are two values to
consider. The peak load current (I
LOAD(MAX)
) deter-
mines the instantaneous component stress and fil-
tering requirements and thus drives output
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The continu-
ous load current (I
LOAD
) determines the thermal
stress and thus drives the selection of input capaci-
tors, MOSFETs, and other critical heat-contributing
components. Modern notebook CPUs generally
exhibit, I
LOAD
= I
LOAD(MAX)
x 0.8.
3)
Switching frequency.
The MAX1762/MAX1791
have a nominal switching frequency of 300kHz.
4)
Inductor ripple-current ratio (LIR).
LIR is the ratio
of the peak-to-peak ripple current to the average
inductor current. Size and efficiency trade-offs must
be considered when setting the inductor ripple-cur-
rent ratio. Low inductor values cause large ripple
currents, resulting in the smallest size but poor effi-
ciency and high output noise. The minimum practi-
cal inductor value is one that causes the circuit to
operate at critical conduction (where the inductor
current just touches zero with every cycle). Inductor
values lower than this grant no further size-reduc-
tion benefit.
The MAX1762/MAX1791s
’
pulse-skipping algorithm ini-
tiates skip mode at the critical conduction point. So, the
inductor operating point also determines the load-cur-
rent value at which switchover occurs. The optimum
point is usually found between 20% and 50% ripple
current.
The inductor ripple current also impacts transient-
response performance, especially at low V
VP
- V
OUT
difference. Low inductor values allow the inductor cur-
rent to slew faster, replenishing charge removed from
the output filter capacitors by a sudden load step. The
peak amplitude of the output transient (V
SAG
) is also a
function of the maximum duty factor, which can be cal-
culated from the on-time and minimum off-time:
where minimum off-time = 0.5μs (max).
Inductor Selection
The switching frequency (on-time) and operating point
(% ripple or LIR) determine the inductor value as fol-
lows:
Example: I
LOAD(MAX)
= 2A, V
VP
= 7V, V
OUT
= 1.6V, f =
300kHz, 35% ripple current or LIR = 0.35:
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice. The core must be large
enough not to saturate at the peak inductor current
(I
PEAK
):
I
PEAK
= I
LOAD(MAX)
+ [(LIR/2)
I
LOAD(MAX)
]
Determining Current Limit
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The val-
ley of the inductor current occurs at I
LOAD(MAX)
minus
half of the ripple current; therefore:
I
VALLEY
> I
LOAD(MAX)
- [(LIR/2)
I
LOAD(MAX)
]
where I
VALLEY
= minimum current-limit threshold volt-
age divided by the R
DS(ON)
of Q2. For the MAX1762/
MAX1791, the minimum current-limit threshold is 90mV.
Use the worst-case maximum value for R
DS(ON)
from
the MOSFET Q2 data sheet, and add some margin for
the rise in R
DS(ON)
with temperature. A good general
rule is to allow 0.5% additional resistance for each
°
C of
temperature rise.
L
kHz
A
H
=
×
=
1.6V(7V-1.6V)
7 300
0 35 2
.
5 9
.
μ
L
=
× ×
×
V
(V
LIR
-V
I
LOAD(MAX)
)
V
OUT
VP
OUT
VP
V
)
L
V
V
+t
V
- V
V
VP
- t
SAG
LOAD(MAX)
(
I
OUT
VP
OFF(MIN)
OUT
OUT
V
VP
OUT
OFF(MIN)
2
=
×
×
×
K
C
K
2
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1791EUB+ | 功能描述:DC/DC 開關(guān)控制器 Step-Down for Notebook 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 |
| MAX1791EUB+ | 制造商:Maxim Integrated Products 功能描述:CONTROLLER ((NW)) |
| MAX1791EUB+T | 功能描述:DC/DC 開關(guān)控制器 Step-Down for Notebook 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 |
| MAX1791EUB-T | 功能描述:DC/DC 開關(guān)控制器 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 |
| MAX1791EVKIT | 功能描述:DC/DC 開關(guān)控制器 Evaluation Kit for the MAX1791 MAX1762 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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