參數(shù)資料
型號(hào)： LM5033
廠商： National Semiconductor Corporation
英文描述： 100V Push-Pull Voltage Mode PWM Controller
中文描述： 100V的推挽式電壓模式PWM控制器
文件頁(yè)數(shù)： 8/16頁(yè)
文件大?。?/td> 295K
代理商： LM5033
Functional Description
The LM5033 High Voltage PWM controller contains all of the
features needed to implement Push-Pull and Bridge topolo-
gies, using voltage-mode control in a small 10 pin package.
Features included are: startup regulator, precision 2.5V ref-
erence output, current limit detection, alternating gate driv-
ers, sync capability, thermal shutdown, softstart, and remote
shutdown. This high speed IC has total propagation delays
<
100 ns. These features simplify the design of an open loop
DC-DC converter, or a voltage controlled closed loop con-
verter. The Functional Block Diagram is shown in
Figure 1
.
High Voltage Start-Up Regulator
(Pins 1, 4)
The LM5033 contains an internal high voltage startup regu-
lator. The input pin (V
) can be connected directly to line
voltages as high as 90V for normal operation, and can
withstand transients to 100V. The regulator output at V
(9.6V) is internally current limited and sources a minimum of
20mA. Upon power up, the capacitor at V
will charge up,
providing a time delay while internal circuits stabilize. When
V
reaches the upper threshold of the under-voltage sen-
sor (typically 9.5V), the under-voltage sensor resets, en-
abling the output drivers, although the PWM duty cycle will
initially be at zero.As the Softstart capacitor then charges up
(described below) the output duty cycle will increase until
regulated by the PWM control loop. The value of the V
capacitor which affects the above mentioned delay depends
on the total system design and its start-up characteristics.
The recommended range of values for the V
CC
capacitor is
0.1 to 50μF.
The lower threshold of the under-voltage sensor is typically
at 6.8V. If V
CC
falls below this value the outputs are disabled
and the softstart capacitor is discharged. When V
CC
is again
increased above the upper threshold the outputs are en-
abled, and the softstart sequence repeats.
The LM5033’s internal power dissipation can be reduced by
powering V
CC
from an external supply. Typically this is done
by means of an auxiliary transformer winding which is diode
connected to the V
pin to provide 10-15V to V
as the
controller completes the start-up sequence. The externally
applied V
voltage will cause the internal regulator to shut
off. The under-voltage sensor circuit will still function in this
mode, requiring that the external V
capacitor be sized so
that V
never falls below 6.8V. The required current into the
V
pin from the external source is shown in Typical Perfor-
mance Characteristics (I
CC
vs. V
CC
).
If a fault condition occurs such that the external supply to
V
fails, external current draw from the V
pin must be
limited as to not exceed the regulator’s current limit, or the
maximum power dissipation of the IC. An external start-up or
other bias rail can be used instead of the internal start-up
regulator by connecting the V
and the V
pins together
and feeding the external bias voltage (10-15V) into that
node.
A thermal shutdown protection will activate if the die tem-
perature exceeds 165
o
C, disabling the outputs (OUT1 and
OUT2), and shutting down the V
CC
regulator. When the die
temperature has reduced below 150C (typical hysteresis =
15C) the V
CC
regulator is enabled and a softstart sequence
will initiate.
Reference (Pin 2)
The Ref pin provides a reference voltage of 2.5V,
±
2.4%.
The pin is internally connected to an NMOS FET drain at the
buffer amplifier’s output, allowing it to sink, but not source
current. An external pullup resistor is required. Current into
the pin must be limited to less than 20 mA to maintain
regulation. See the graph in the Typical Performance Char-
acteristics.
During start-up if the pullup voltage is present before the
reference amplifier establishes regulation, the voltage on pin
2 must not exceed 5.5V. If this reference is not used the Ref
pin can float or be connected to ground.
PWM Comparator (Pin 3), Duty
Cycle and Deadtime
The PWM comparator compares an internal ramp signal (0 -
0.65V) with the loop error voltage derived from the Comp pin
(pin 3). The Comp voltage is typically set by an external error
amplifier through an optocoupler for closed loop applica-
tions. Internally, the voltage at the Comp pin passes through
two level shifting diodes, and a gain reducing 3:1 resistor
divider. The output of the PWM comparator provides the
pulse width information to the output drivers (Out1 and
Out2). This comparator is optimized for speed in order to
achieve minimum discernable duty cycles. The output duty
cycle is 0% for V
<
1.5V, and maximum for V
>
3.5V. See the Typical Performance Characteristics. The
maximum duty cycle for each output is limited to less than
50% due to the forced deadtime. The typical deadtime be-
tween the falling edge of one gate driver output and the
rising edge of the other gate driver output is 135 ns, and
does not vary with frequency. The maximum duty cycle for
each output can be calculated from:
where T
is the period of each output, and T
is the dead-
time. For example, if the oscillator frequency is 200 kHz,
each output will cycle at 100 kHz, and T
S
= 10 μs. Using the
nominal deadtime of 135 ns, the maximum duty cycle at this
frequency is 48.65%. Using the minimum deadtime of 85 ns,
the maximum duty cycle increases to 49.15%.
When the Softstart pin (pin 10) is pulled down (internally or
externally) the Comp pin voltage is pulled down with it, with
a difference of 0.5V. When the Softstart pin voltage in-
creases the Comp voltage is allowed to increase, pulled up
by an internal 5.2V supply through a 5k
resistor.
In an open loop application, such as an intermediate bus
converter, pin 3 can be left open resulting in maximum duty
cycle at the output drivers .
Current Sense (Pin 8)
The current sense circuit is intended to protect the power
converter when an abnormal primary current is sensed by
initiating a low duty cycle hiccup mode. When the threshold
(0.5V) at Pin 8 is exceeded the outputs are disabled, and the
softstart capacitor (at pin 10) is internally discharged. When
the softstart capacitor is fully discharged
and
the voltage at
the CS pin is below 0.5V, the outputs are re-enabled allowing
the softstart capacitor voltage and the output duty cycle to
increase.
L
www.national.com
8
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LM5033_05 制造商:NSC 制造商全稱:National Semiconductor 功能描述:100V Push-Pull Voltage Mode PWM Controller
LM5033MM 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?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開(kāi)關(guān)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
LM5033MM/MEY8 制造商:Texas Instruments 功能描述:
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LM5033MMX 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?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開(kāi)關(guān)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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