參數(shù)資料
型號(hào)： MAX1813EEI
廠商： MAXIM INTEGRATED PRODUCTS INC
元件分類： 穩(wěn)壓器
英文描述： Dynamically-Adjustable, Synchronous Step-Down Controller with Integrated Voltage Positioning
中文描述： SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO28
封裝： 0.150 INCH, 0.025 INCH PITCH, QSOP-28
文件頁(yè)數(shù)： 26/38頁(yè)
文件大?。?/td> 738K
代理商： MAX1813EEI
M
Dynamically-Adjustable, Synchronous Step-Down
Controller with Integrated Voltage Positioning
26
______________________________________________________________________________________
where:
For a standard 300kHz application, the ESR zero fre-
quency must be well below 95kHz, preferably below
50kHz. Tantalum, Sanyo POSCAP, and Panasonic SP
capacitors in wide-spread use at the time of publication
have typical ESR zero frequencies below 30kHz. In the
standard application used for inductor selection, the
ESR needed to support a 30mVp-p ripple is 30mV/(22A
x 0.3) = 4.5m
. Six 220μF/2.5V Panasonic SP capaci-
tors in parallel provide 2.5m
(max) ESR. The capaci-
tors
’
typical ESR results in a zero at 48kHz.
Don
’
t put high-value ceramic capacitors directly across
the output without taking precautions to ensure stability.
Ceramic capacitors have a high ESR zero frequency
and may 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 the FB pin.
Unstable operation manifests itself in two related but
distinctly different ways: double-pulsing and 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 minimum off-time period has expired.
Double-pulsing is more annoying than harmful, result-
ing 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 cause the out-
put voltage to rise above or fall below the tolerance
limit.
The easiest method for checking stability is to apply a
very fast zero-to-max load transient and carefully
observe the output voltage ripple envelope for over-
shoot and ringing. It can help to monitor simultaneously
the inductor current with an AC current probe. Don
’
t
allow more than one cycle of ringing after the initial
step-response under/overshoot.
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (I
RMS
) imposed by the switching currents
defined by the following equation:
For most applications, nontantalum chemistries (ceram-
ic, aluminum, or OS-CON) are preferred due to their
resistance to inrush surge currents typical of systems
with a mechanical switch or connector in series with the
input. If the MAX1813 is operated as the second stage
of a two-stage power-conversion system, tantalum
input capacitors are acceptable. In either configuration,
choose an input capacitor that exhibits less than +10
°
C
temperature rise at the RMS input current for optimal
circuit longevity.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
(>20A) when using high-voltage (>20V) AC adapters.
Low-current applications usually require less attention.
The high-side MOSFET (Q
H
) must be able to dissipate
the resistive losses plus the switching losses at both
V
IN(MIN)
and V
IN(MAX)
. Calculate both of these sums.
Ideally, the losses at V
IN(MIN)
should be roughly equal
to losses at V
IN(MAX)
, with lower losses in between. If
the losses at V
IN(MIN)
are significantly higher than the
losses at V
IN(MAX)
, consider increasing the size of Q
H
.
Conversely, if the losses at V
IN(MAX)
are significantly
higher than the losses at V
IN(MIN)
, consider reducing
the size of Q
H
. If V
IN
does not vary over a wide range,
the minimum power dissipation occurs where the resis-
tive losses equal the switching losses.
Choose a low-side MOSFET that has the lowest possi-
ble on-resistance (R
DS(ON)
), comes in a moderate-
sized package (i.e., one or two SO-8s, DPAK or
D
2
PAK), and is reasonably priced. Make sure that the
DL gate driver can supply sufficient current to support
the gate charge and the current injected into the para-
sitic gate-to-drain capacitor caused by the high-side
MOSFET turning on; otherwise, cross-conduction prob-
lems may occur.
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET (Q
H
), the worst-
case power dissipation due to resistance occurs at the
minimum input voltage:
I
=I
V
(V
V
- V
)
RMS
LOAD
OUT
IN
OUT
IN
ESR
ESR OUT
=
1
2 R
ESR
SW
π
=
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX1813EEI+ 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
MAX1813EEI+T 功能描述:DC/DC 開關(guān)控制器 Dynamically Adjustable Synchronous Step-Down Controller w/Integrated Voltage Positioning 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
MAX1813EEI-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
MAX1813EVKIT 功能描述:DC/DC 開關(guān)控制器 Evaluation Kit for the MAX1813 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
MAX1813XR46+ 制造商:Maxim Integrated Products 功能描述:
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