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| 型號： | NCP1239 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | Low−Standby High Performance PWM Controller |
| 文件頁數(shù)： | 24/38頁 |
| 文件大小： | 1145K |
| 代理商： | NCP1239 |
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NCP1239
http://onsemi.com
24
If by design we have selected a 47 F V
CC
capacitor, it
becomes easy to evaluate the burst period and its dutycycle.
This can be done by properly identifying all time events on
Figure 42 and applying the classical formula:
t = C * V / i
.
To simplify, let’s consider t1 starts while V
CC
= V
CCOFF
.
Then:
t1: I = I
CC
3 = 400 A, V= 11.2 – 6.9 = 3 V
t1 = 505 ms
t2: I = 3.6 mA, V= 16.4 – 6.9 = 9.5 V
t3: I = 400 A, V= 16.4 – 11.2 = 5.2 V
t’1 = t1= 505 ms
t’2 = t2 = 124 ms
The total period duration is thus the sum of all these events
which leads to Tfault = 1793 ms. If Tpulse = 100 ms, then
our burst dutycycle equals 100/(1869 + 100)
≈
5%, which
is excellent.
In fact, the calculation assumption, t1 starts while
V
CC
= V
CCOFF
, gives the worse case since the duty cycle is
calculated in the case where Tpulse exactly equals the active
phase duration (switching period when V
CC
decreases from
V
CCON
to V
CCOFF
).
t2 = 124 ms
t3 = 611 ms
In fact, Tpulse is generally:
shorter than the switching phase period. In this
case, t1 is longer since the latched off phase starts
earlier (at a V
CC
higher than V
CCOFF
). As a
consequence, the final duty cycle is lower than
previously estimated,
longer than the switching phase period. In this case,
the circuit detects an overload condition simply
because V
CC
drops below V
CCOFF
(11.2 V) before
the fault timer has elapsed. Tpulse is lower than 100
ms and as a result the duty cycle is also lower.
(Major) Fault Detection and Latched Off Mode
The NCP1239 features a fast comparator that
permanently monitors the “Fault Detect” pin level. If for any
reason this level exceeds 2.4 V (typical), the part
immediately stops oscillating and stays latched off until the
user cycles down the power supply. This enables the SMPS
designer to externally shut down the part in particular when
a major default occurs, e.g. an Overvoltage Protection
(OVP). Figure 43 shows what happens when the part is
latched:
V
CCOFF
Figure 43.
Drv
Latchoff phase level
Logic reset level
Pin 3
Stop!
2.4 V
When Vpin3 exceeds 2.4 V, NCP1239 permanently latchesoff the output pulses
illustrate a case where a thermistor supplied by REF5V is connected to Pin 3 to detect excessive temperatures of the application
(refer to application schematic).
until its V
CC
goes below 4 V. The figure can
The user has unplugged, reset!
V
CC
V
CCON
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相關(guān)代理商/技術(shù)參數(shù) |
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| NCP1239D | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Low-Standby High Performance PWM Controller |
| NCP1239F | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators |
| NCP1239FDR2 | 功能描述:電流型 PWM 控制器 Low Standby Power RoHS:否 制造商:Texas Instruments 開關(guān)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 |
| NCP1239FDR2G | 功能描述:電流型 PWM 控制器 Low Standby Power High Performance PWM RoHS:否 制造商:Texas Instruments 開關(guān)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 |
| NCP1239V | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators |
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