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參數(shù)資料
| 型號： | MAX8540 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Synchronizable. High-Frequency Current- and Voltage-Mode PWM Controllers for Isolated Supplies |
| 中文描述： | 可同步、高頻、電流或電壓模式PWM控制器，用于隔離電源 |
| 文件頁數(shù)： | 11/16頁 |
| 文件大小： | 328K |
| 代理商： | MAX8540 |
where R
PRAMP
is in k
. The ramp-voltage magnitude is
independent of frequency. The range of values for
R
PRAMP
is from 12.4k
to 42k
.
Soft-Start
The soft-start feature allows converters built using the
MAX8540/MAX8541 to apply power to the load in a
controllable soft ramp, thus reducing startup surges
and stresses. It also determines power-up sequencing
when several converters are used.
Upon power turn-on, the soft-start pin acts as a current
sink to discharge any capacitance connected to it. Once
the voltage at V
CC
has exceeded its lockout value, soft-
start then charges the external capacitor (C
SS
), allowing
the converter output voltage to ramp up. Full output volt-
age is reached in approximately 440ms/μF.
Current Limit
The MAX8540/MAX8541 utilize two current-limit
schemes: cycle-by-cycle current limit and short-circuit
current limit. Set the current-limit threshold using a
resistor-divider from REF to GND with ILIM connected to
the center. The current-limit threshold is determined as:
where R5 is the resistor from ILIM to GND and R6 is the
resistor from REF to ILIM. Use 240k
for R16 and vary
R23 to change the threshold.
The CS signal provides feedback on the current ramp
through the main external MOSFET. The voltage on CS
is monitored by the IC. The cycle-by-cycle current limit
abbreviates the on-time of the external MOSFET in the
event that the voltage at CS is greater than the thresh-
old voltage set by ILIM.
The current-limit feature protects against a hard short
or overcurrent fault at the output by one of two selected
protection modes: by latching off the output, or pulsing
the output to reduce the average output current
(hiccup mode).
To select latched mode, connect SKTOFF to REF. In
this mode, if the hard short exists for the time period set
by the capacitance at SKTON, the output is latched off.
To unlatch the output, toggle
EN
or cycle the input
power to V
CC
.
To select hiccup mode, connect capacitors to SKTON
and SKTOFF to program the hiccup mode on- and off-
times. When a cycle-by-cycle event is detected, the IC
charges the capacitor at SKTON. The capacitor contin-
ues to charge as long as the CS voltage is greater than
the ILIM threshold voltage. Once the voltage on SKTON
reaches its threshold voltage, the MAX8540/MAX8541
begin skipping switching cycles for a time determined
by the capacitance connected to SKTOFF. Once this
time period has elapsed, the IC begins to switch for the
time period set by the capacitance connected to
SKTON. This process continues until the output short is
removed. See the
SKTON and SKTOFF
section for
details on setting the hiccup-mode periods.
Connect SKTOFF to REF and SKTON to GND to disable
the latched-mode and hiccup-mode protection, and
operate continuously in cycle-by-cycle current-limit.
PMW Comparator
The PWM comparator of the MAX8540 transforms the
optocoupled error voltage (V
OPTO
) into a duty cycle by
comparing the opto feedback-error voltage with a
summed voltage. The summed voltage is the sum of
the programmable slope compensation and the cur-
rent-sense voltages. When the summed voltage
exceeds the opto feedback error voltage, the gate-
drive logic turns off the external MOSFET.
The PWM comparator in the MAX8541 compares
V
OPTO
with the programmable voltage ramp. When the
voltage ramp exceeds V
OPTO
, the gate-driver logic
turns off the external MOSFET.
SKTON and SKTOFF
The capacitance, C
SKTON
, determines the time period
allowed before the short-circuit current limit initiates.
Once the CS voltage exceeds the ILIM threshold, the
capacitor at SKTON begins to charge. The capacitor
continues to charge until the SKTON threshold voltage
is reached or the overcurrent event is removed. This
feature allows for the higher currents required during
startup with high-capacitance loads. Set C
SKTON
to
allow sufficient time for startup. The required capaci-
tance at SKTON is determined as:
C
SKTON
= t
ON
/ 10
3
where t
ON
is in ms and C
SKTON
is in μF. The allowable
range for C
SKTON
is 100pF to 0.01μF.
The capacitance at SKTOFF determines the time period
that the external MOSFET is turned off during an over-
current event. Once the SKTON time period is exceeded,
the SKTOFF capacitor charges. Once V
SKTOFF
reaches
its threshold, the IC begins to switch again. C
SKTOFF
is
determined as:
C
SKTOFF
= t
OFF
/ 10
3
where t
OFF
is in ms and C
SKTOFF
is in μF. The allow-
able range for C
SKTOFF
is 1000pF to 1μF.
V
R
R
R
V
ILIM
REF
=
+
×
5
5
6
M
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
______________________________________________________________________________________________________
11
相關PDF資料 |
PDF描述 |
|---|---|
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| MAX8540EEE | Synchronizable, High-Frequency Current- and Voltage-Mode PWM Controllers for Isolated Supplies |
| MAX8541EEE | Synchronizable, High-Frequency Current- and Voltage-Mode PWM Controllers for Isolated Supplies |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX8540EEE | 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8540EEE+ | 功能描述:電流型 PWM 控制器 Synchronizable PWM Controller RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8540EEE+T | 功能描述:電流型 PWM 控制器 PWM Controller Curr-Mode RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8540EEE-T | 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8541EEE | 功能描述:電壓模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
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