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參數(shù)資料
| 型號(hào)： | MAX1685EEE |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | Low-Noise, 14V Input, 1A, PWM Step-Down Converters |
| 中文描述： | 2.3 A SWITCHING REGULATOR, 680 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 0.150 INCH, 0.025 INCH PITCH, QSOP-16 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大?。?/td> | 234K |
| 代理商： | MAX1685EEE |
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Low-Noise, 14V Input, 1A, PWM
S tep-Down Converters
10
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inductor peak current during the first half of each cycle,
based on the output error voltage. The MAX1684/
MAX1685’s loop gain is relatively low to enable the use
of a small, low-valued output filter capacitor. The 1.4%
transient load regulation from 0 to 1A is compensated
by an integrator circuit that lowers DC load regulation
to 0.01% typical. Slope compensation accounts for the
inductor-current waveform’s down slope during the
second half of each cycle, and eliminates the inductor-
current staircasing characteristic of current-mode con-
trollers at high duty cycles.
PFM Control
In low-power mode, the MAX1684/MAX1685 devices
switch only as needed to service the load. This reduces
the switching frequency and associated losses in the
P-channel switch, the synchronous rectifier, and the
external inductor. During this PFM operation, a switch-
ing cycle initiates when the PFM comparator senses
that the output voltage has dropped too low. The
P-channel MOSFET switch turns on and conducts cur-
rent to the output-filter capacitor and load. The
MAX1684/MAX1685 then wait until the PFM comparator
senses a low output voltage again.
In normal mode at light load (<150mA), the device also
operates in PFM. The PFM current comparator controls
both entry into PWM mode and the peak switch current
during PFM operation. Consequently, some jitter is nor-
mal during transition from PFM to PWM with loads
around 150mA, and it has no adverse impact on regu-
lation.
100% Duty-Cyc le Operation
As the input voltage drops, the duty cycle increases
until the P-channel MOSFET turns on continuously,
achieving 100% duty cycle. Dropout voltage in 100%
duty cycle is the output current multiplied by the on-
resistance of the internal switch and inductor, approxi-
mately 0.35V (I
OUT
= 1A).
V ery Low Duty-Cyc le Operation
Because of the P-channel minimum on-time and dead-
time (duration when both switches are off), the
MAX1684/MAX1685’s switching frequency must
decrease in PWM or normal mode to maintain regulation
at a very low duty cycle. The total P-channel on-time and
dead-time is 290ns typical. As a result, the MAX1684/
MAX1685 will maintain fixed-frequency regulation at no
load for V
IN
up to 10V
OUT
and 5V
OUT
, respectively (see
PWM Fixed-Frequency Operation Area graph in the
Typical Operating Characteristics). For higher V
IN
at no
load, the frequency decreases based on the following
equation:
f = V
OUT
/ (V
IN
·
290ns)
At medium- to full-load current (>100mA), V
IN
can
increase slightly higher before the frequency decreases.
S ync hronous Rec tific ation
Although the primary rectifier is an external Schottky
diode, a small internal N-channel synchronous rectifier
allows PWM operation at light loads. During the second
half of each cycle, when the inductor current ramps
below the zero-crossing threshold or when the oscilla-
tor period ends, the synchronous rectifier turns off. This
keeps excess current from flowing backward through
the inductor. Choose an appropriate inductor to limit
the PWM ripple current through the N-channel FET to
400mAp-p.
Current Limit and S oft-S tart
The voltage at ILIM/SS sets the PWM current limit
(I
LIM
= 1.75A) and the low-power current limit (I
LIMLP
=
380mA). The PWM current limit applies when the
device is in PWM mode, in synchronized PWM mode,
or delivering a heavy load in normal mode (Table 1).
The I
LIMLP
limit applies when the device is in low-power
mode. An internal 4μA current source pulls ILIM/SS up
to CVL. To use the maximum current-limit thresholds,
leave ILIM/SS unconnected or connect it to a soft-start
capacitor. Connect an external resistor from ILIM/SS to
AGND to adjust the current-limit thresholds.
The PWM current-limit threshold is (I
LIM
·
R
ILIM/SS
·
4μA) / V
REF
and is adjustable from 0.5A to 1.75A.
The low-power current-limit threshold is equal to (I
LIMLP
·
R
ILIM/SS
·
4μA) / V
REF
and is adjustable from 110mA to
380mA.
For example, when R
ILIM/SS
is 156k
, the PWM current
limit threshold is 0.88A and the low-power current limit
threshold is 0.19A.
Connect a low-value capacitor from ILIM/SS to AGND
to achieve soft-start, limiting inrush current. ILIM/SS
internally shorts to AGND in shutdown to discharge the
soft-start capacitor. Do not connect ILIM/SS to REF or
CVL. Determine the soft-start duration by:
t
SOFT-START
= C
ILIM/SS
(1.25V / 4μA)
where t
SOFT-START
is the time from SHDN going high to
the regulator being able to supply full load current. For
example, a 0.1μF capacitor yields 31ms of soft-start.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1685EEE+ | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 14V 1A PWM Step-Down Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1685EEE+T | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 14V 1A PWM Step-Down Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1685EEE-T | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 14V 1A PWM Step-Down Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1685EVKIT | 功能描述:電源管理IC開(kāi)發(fā)工具 Evaluation Kit for the MAX1684 MAX1685 RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類(lèi)型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| MAX1686EUA | 功能描述:電荷泵 3-5V Regulating Chrg Pump For SIM Cards RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 輸出電壓:- 1.5 V to - 5.5 V, 3 V to 11 V 輸出電流:100 mA 電源電流:1 mA 最大工作溫度:+ 70 C 封裝 / 箱體:SOIC-8 Narrow 封裝:Tube |
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