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參數(shù)資料
| 型號： | MAX1994ETM |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Step-Down Controllers Plus Linear- Regulator Controller for Notebook Computers |
| 中文描述： | DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, CQCC48 |
| 封裝： | 7 X 7 MM, 0.80 MM HEIGHT, THIN, QFN-48 |
| 文件頁數(shù)： | 39/49頁 |
| 文件大?。?/td> | 983K |
| 代理商： | MAX1994ETM |
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M
Dual Step-Down Controllers Plus Linear-
Regulator Controller for Notebook Computers
______________________________________________________________________________________
39
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:
where I
LIMIT(MIN)
equals the minimum current-limit
threshold voltage divided by the current-sense resistor.
The sense resistor (R2 in Figure 1) determines the achiev-
able current-limit accuracy. There is a trade-off between
current-limit accuracy and sense-resistor power dissipa-
tion. Most applications employ a current-sense voltage of
50mV to 100mV. Choose a sense resistor so that:
where 0.8 is a factor for worst-case low current-limit
threshold.
Extremely cost-sensitive applications that do not require
high-accuracy current sensing can use the on-resis-
tance of the low-side MOSFET switch in place of the
sense resistor by connecting CS2 to LX2. Use the worst-
case maximum value for R
DS(ON)
from the MOSFET
data sheet taking into account the rise in R
DS(ON)
with
temperature. A good general rule is to allow 0.5% addi-
tional resistance for each
°
C temperature rise.
Assume the current-sense resistor in the application cir-
cuit in Figure 1 is removed and CS2 is directly tied to
LX2. The Q4 maximum R
DS(ON)
= 3.8m
at T
J
= +25
°
C
and 5.7m
at T
J
= +125
°
C.
The minimum current-limit threshold is:
mV
LIMIT MIN
(
)
=
and the required valley current limit is:
I
LIMIT(MIN)
> 7A
(1 - 0.30/2) = 5.95A
since 7A is greater than the required 5.95A, the circuit
can deliver the 7A full-load current.
Output Capacitor Selection
(BUCK1 and BUCK2)
The output filter capacitor must have low enough effec-
tive series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements. Also, the capacitance
value must be high enough to absorb the inductor ener-
gy going from a full-load to no-load condition without
tripping the OVP circuit.
In CPU core voltage regulators and other applications
where the output is subject to violent load transients,
the output capacitor
’
s size typically depends on how
much ESR is needed to prevent the output from dipping
too low under a load transient. Ignoring the sag due to
finite capacitance:
In non-CPU applications, the output capacitor
’
s size
often depends on how much ESR is needed to maintain
an acceptable level of output-voltage ripple:
The actual microfarad capacitance value required often
relates to the physical size needed to achieve low ESR,
as well as to the chemistry of the capacitor technology.
Thus, the capacitor is usually selected by ESR and volt-
age rating rather than by capacitance value (this is true
of tantalums, OSCONs, and other electrolytics).
When using low-capacity filter capacitors such as
ceramic or polymer types, capacitor size is usually deter-
mined by the capacity needed to prevent V
SAG
and
V
SOAR
from causing problems during load transients.
Generally, once enough capacitance is added to meet
the overshoot requirement, undershoot at the rising load
edge is no longer a problem.
The amount of overshoot due to stored inductor energy
can be calculated as:
where I
PEAK
is the peak inductor current.
V
L I
C
OUT
V
SOAR
PEAK
OUT
=
×
×
2
2
R
V
LIR I
ESR
P P
LOAD MAX
≤
(
)
R
V
I
ESR
DIP
LOAD MAX
≤
(
)
I
m
A
.
.
.
×
=
500
0 1 0 8
5 7
7
R
mV
I
V
Fixed Mode
(
R
I
Adjustable Mode
(
SENSE
LIMIT MIN
SENSE
ILIM
LIMIT MIN
=
×
=
×
50
0 8
.
0 1 0 8
.
2
)
.
)
(
)
(
)
I
I
LIR
2
LIMIT MIN
LOAD MAX
(
)
(
)
>
×
1
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1994ETM+ | 功能描述:DC/DC 開關控制器 Integrated Circuits (ICs) RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM+T | 功能描述:DC/DC 開關控制器 Integrated Circuits (ICs) RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM-T | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994EVKIT | 功能描述:DC/DC 開關控制器 Evaluation Kit for the MAX1816 MAX1980 MAX1994 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1995EGI | 功能描述:顯示驅動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
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