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參數(shù)資料
| 型號： | MAX1715 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Ultra-High Efficiency, Dual Step-Down Controller for Notebook Computers |
| 中文描述： | 超高效率、雙路降壓型控制器，用于筆記本電腦 |
| 文件頁數(shù)： | 19/28頁 |
| 文件大?。?/td> | 308K |
| 代理商： | MAX1715 |
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M
Ultra-High Efficiency, Dual Step-Down
Controller for Notebook Computers
______________________________________________________________________________________
19
The amount of overshoot due to stored inductor energy
can be calculated as:
where I
PEAK
is the peak inductor current.
Output Capacitor Stability Considerations
Stability is determined by the value of the ESR zero rel-
ative to the switching frequency. The point of instability
is given by the following equation:
where:
For a typical 300kHz application, the ESR zero frequen-
cy must be well below 95kHz, preferably below 50kHz.
Tantalum and OS-CON capacitors in widespread use
at the time of publication have typical ESR zero fre-
quencies of 15kHz. In the design example used for
inductor selection, the ESR needed to support 50mVp-p
ripple is 50mV/3.5A = 14.2m
. Three 470μF/4V Kemet
T510 low-ESR tantalum capacitors in parallel provide
15m
max ESR. Their typical combined ESR results in
a zero at 14.1kHz, well within the bounds of stability.
Don’t put high-value ceramic capacitors directly across
the fast feedback inputs (FB_ to AGND) without taking
precautions to ensure stability. Large ceramic capaci-
tors can have a high-ESR zero frequency and cause
erratic, unstable operation. However, it’s easy to add
enough series resistance by placing the capacitors a
couple of inches downstream from the junction of the
inductor and FB_ pin (see the
All-Ceramic-Capacitor
Application
section).
Unstable operation manifests itself in two related but
distinctly different ways: double-pulsing and fast-feed-
back loop instability.
Double-pulsing occurs due to noise on the output or
because the ESR is so low that there isn’t enough volt-
age ramp in the output voltage signal. This “fools” the
error comparator into triggering a new cycle immedi-
ately after the 400ns minimum off-time period has
expired. Double-pulsing is more annoying than harmful,
resulting in nothing worse than increased output ripple.
However, it can indicate the possible presence of loop
instability, which is caused by insufficient ESR.
Loop instability can result in oscillations at the output
after line or load perturbations that can trip the overvolt-
age protection latch or cause the output voltage to fall
below the tolerance limit.
The easiest method for checking stability is to apply a
very fast zero-to-max load transient (refer to the
MAX1715 EV kit manual) and carefully observe the out-
put voltage ripple envelope for overshoot and ringing. It
can help to simultaneously monitor the inductor current
with an AC current probe. Don’t allow more than one
cycle of ringing after the initial step-response under- or
overshoot.
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (IRMS) imposed by the switching currents.
Nontantalum chemistries (ceramic, aluminum, or OS-
CON) are preferred due to their resistance to power up
surge currents.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
(>5A) when using high-voltage (>20V) AC adapters.
Low-current applications usually require less attention.
For maximum efficiency, choose a high-side MOSFET
(Q1) that has conduction losses equal to the switching
losses at the optimum battery voltage (15V). Check to
ensure that the conduction losses at the
minimum
input voltage don’t exceed the package thermal limits
or violate the overall thermal budget. Check to ensure
that conduction losses plus switching losses at the
maximum
input voltage don’t exceed the package rat-
ings or violate the overall thermal budget.
Choose a low-side MOSFET (Q2) that has the lowest
possible R
DS(ON)
, comes in a moderate to small pack-
age (i.e., SO-8), and is reasonably priced. Ensure that
the MAX1715 DL gate driver can drive Q2; in other
words, check that the gate isn’t pulled up by the high-
side switch turning on due to parasitic drain-to-gate
capacitance, causing cross-conduction problems.
Switching losses aren’t an issue for the low-side MOS-
FET since it’s a zero-voltage switched device when
used in the buck topology.
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET, the worst-case-
I
I
V
V
-V
V
RMS
LOAD
OUT
IN
OUT
IN
=
(
)
f
R
C
ESR
ESR
F
=
1
2
π
f
f
π
ESR
=
V LI
2
2CV
PEAK
OUT
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1715EEI | Ultra-High Efficiency, Dual Step-Down Controller for Notebook Computers |
| 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 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1715EEI | 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 |
| MAX1715EEI+ | 功能描述:DC/DC 開關(guān)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(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 |
| MAX1715EEI+T | 功能描述:DC/DC 開關(guān)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(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 |
| MAX1715EEI-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 |
| MAX1715EVKIT | 功能描述:DC/DC 開關(guān)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(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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