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參數資料
| 型號： | MAX1715EEI |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Ultra-High Efficiency, Dual Step-Down Controller for Notebook Computers |
| 中文描述： | DUAL SWITCHING CONTROLLER, 620 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | 0.150 INCH, 0.025 INCH PITCH, MO-137AD QSOP-28 |
| 文件頁數： | 18/28頁 |
| 文件大?。?/td> | 308K |
| 代理商： | MAX1715EEI |
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M
Ultra-High Efficiency, Dual Step-Down
Controller for Notebook Computers
18
______________________________________________________________________________________
The inductor ripple current also impacts transient-
response performance, especially at low V
IN
- V
OUT
dif-
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The amount of output sag is also a function of the maxi-
mum duty factor, which can be calculated from the on-
time and minimum off-time:
I
C
DUTY V
F
2
where
where minimum off-time = 400ns typ (see Table 5).
Inductor Selection
The switching frequency (on-time) and operating point
(% ripple or LIR) determine the inductor value as fol-
lows:
V
(V
V
IN
Example: I
LOAD(MAX)
= 8A, V
IN
= 7V, V
OUT
= 1.6V, f =
300kHz, 35% ripple current or LIR = 0.35:
1.6V (7 - 1 6)
7 300kHz 0.33 8A 1.6 H
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice; although powdered
iron is inexpensive and can work well at 200kHz. 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 the 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
LIMIT(LOW)
> I
LOAD(MAX)
- (LIR / 2) I
LOAD(MAX)
where I
LIMIT(LOW)
= minimum current-limit threshold
voltage divided by the R
DS(ON)
of Q2. For the
MAX1715, the minimum current-limit threshold (100mV
default setting) 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 tempera-
ture. A good general rule is to allow 0.5% additional
resistance for each °C of temperature rise.
Examining the 8A circuit example with a maximum
R
DS(ON)
= 12m
at high temperature reveals the fol-
lowing:
I
LIMIT(LOW)
= 90mV / 12m
= 7.5A
7.5A is greater than the valley current of 6.6A, so the
circuit can easily deliver the full-rated 8A using the
default 100mV nominal ILIM threshold.
Output Capacitor Selection
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
energy going from a full-load to no-load condition with-
out tripping the overvoltage protection circuit.
In CPU V
CORE
converters and other applications where
the output is subject to violent load transients, the out-
put capacitor’s size 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
depends on how much ESR is needed to maintain an
acceptable level of output voltage ripple:
The actual microfarad capacitance value required
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, OS-CONs, and other electrolytics).
When using low-capacity filter capacitors such as
ceramic or polymer types, capacitor size is usually
determined by the capacity needed to prevent VSAG
and VSOAR from causing problems during load tran-
sients. Also, the capacitance must be great enough to
prevent the inductor’s stored energy from launching the
output above the overvoltage protection threshold.
Generally, once enough capacitance is added to meet
the overshoot requirement, undershoot at the rising
load edge is no longer a problem (see the VSAG equa-
tion in the
Design Procedure
).
R
Vp p
LIR I
ESR
LOAD MAX
≤
-
(
)
R
V
I
ESR
DIP
(
LOAD MAX
≤
)
L
=
μ
L =
- V
)
OUT
IN
OUT
LOAD(MAX)
DUTY
K (V
+ 0.075V) V
+ 0.075V) V
K (V
+ min off-time
OUT
IN
OUT
OUT
=
V
L
V
-
SAG
LOAD MAX
(
IN MIN
(
OUT
=
(
)
)
(
)
)
2
相關PDF資料 |
PDF描述 |
|---|---|
| MAX1717 | Replaced by TMS320VC5506 : Digital Signal Processors 132-BQFP |
| MAX1717EEG | Replaced by TMS320VC5506 : Digital Signal Processors 100-LQFP |
| MAX1718EEI | Notebook CPU Step-Down Controller for Intel Mobile Voltage Positioning IMVP-II |
| MAX1718 | Replaced by TMS320VC5506 : Digital Signal Processors 100-LQFP -40 to 85 |
| MAX1718BEEI | Notebook CPU Step-Down Controller for Intel Mobile Voltage Positioning IMVP-II |
相關代理商/技術參數 |
參數描述 |
|---|---|
| MAX1715EEI+ | 功能描述:DC/DC 開關控制器 Dual Step-Down Controller 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 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1715EEI+T | 功能描述:DC/DC 開關控制器 Dual Step-Down Controller 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 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1715EEI-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 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1715EVKIT | 功能描述:DC/DC 開關控制器 Evaluation Kit for the MAX1715 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 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1716EEG | 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 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
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