參數(shù)資料
型號(hào)： LM5026MTX
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： Active Clamp Current Mode PWM Controller
中文描述： 3 A SWITCHING CONTROLLER, 660 kHz SWITCHING FREQ-MAX, PDSO16
封裝： TSSOP-16
文件頁(yè)數(shù)： 11/23頁(yè)
文件大?。?/td> 936K
代理商： LM5026MTX
Detailed Operating Description
The LM5026 PWM controller contains all of the features
necessary to implement power converters utilizing the active
clamp reset technique with current mode control. With the
active clamp reset, higher efficiencies and greater power
densities can be realized compared to conventional catch
winding or RDC clamp reset techniques. The LM5026 pro-
vides two control outputs, the main power switch control
(OUT_A) and the active clamp switch control (OUT_B). The
device can be configured to drive either a P-Channel or
N-Channel clamp switch. The main switch gate driver fea-
tures a compound configuration consisting of both MOS and
bipolar devices, which provide superior gate drive character-
istics. The LM5026 can be configured to operate with bias
voltages over a wide input range from 8V to 100V. Additional
features include programmable maximum duty cycle, line
under-voltage lockout, cycle-by-cycle current limit, hiccup
mode fault protection with adjustable delays, PWM slope
compensation, soft-start, a 1MHz capable oscillator with syn-
chronization Input / Output capability, precision reference
and thermal shutdown.
High Voltage Start-Up Regulator
The LM5026 contains an internal high voltage start-up regu-
lator that allows the input pin (VIN) to be connected directly
to a nominal 48V dc line voltage. The regulator output (VCC)
is internally current limited to 20mA. When power is applied
and the UVLO pin potential is greater than 0.4V, the regula-
tor is enabled and sources current into an external capacitor
connected to the VCC pin. The recommended capacitance
range for the VCC regulator is 0.1μF to 100μF. The VCC
regulator provides power to the internal voltage reference,
PWM controller and gate drivers. The controller outputs are
enabled when the voltage on the VCC pin reaches the
regulation point of 7.6V, the internal voltage reference (REF)
reaches its regulation point of 5V and the UVLO voltage is
greater than 1.25V. In typical applications, an auxiliary trans-
former winding is connected through a diode to the VCC pin.
This winding must raise the VCC voltage above 8V to shut
off the internal start-up regulator. Powering VCC from an
auxiliary winding improves efficiency while reducing the con-
troller’s power dissipation.
The external VCC capacitor must be sized such that the
current delivered from the capacitor and the VCC regulator
will maintain a VCC voltage greater than 6.2V during the
initial start-up. During a fault mode when the converter aux-
iliary winding is inactive, external current draw on the VCC
line should be limited such that the power dissipated in the
start-up regulator does not exceed the maximum power
dissipation of the IC package. An external start-up or bias
regulator can be used to power the LM5026 instead of the
internal start-up regulator by connecting the VCC and the
VIN pins together and connecting an external bias supply to
these two pins.
Line Under-Voltage Detector
The LM5026 contains a dual level Under-Voltage Lockout
(UVLO) circuit. When the UVLO pin voltage is below 0.4V
the controller is in a low current shutdown mode. When the
UVLO pin voltage is greater than 0.4V but less than 1.25V,
the controller is in standby mode. In standby mode the VCC
and REF bias regulators are active while the controller out-
puts are disabled. When the VCC and REF outputs exceed
the VCC and REF under-voltage thresholds and the UVLO
pin voltage is greater than 1.25V, the outputs are enabled
and normal operation begins. An external set-point voltage
divider from VIN to GND can be used to set the operational
range of the converter. The divider must be designed such
that the voltage at the UVLO pin will be greater than 1.25V
when VIN is in the desired operating range. UVLO hysteresis
is accomplished with an internal 20uA current source that is
switched on or off into the impedance of the set-point divider.
When the UVLO threshold is exceeded, the current source is
activated to instantly raise the voltage at the UVLO pin.
When the UVLO pin voltage falls below the 1.25V threshold,
the current source is turned off causing the voltage at the
UVLO pin to fall. The hysteresis of the 0.4V shutdown com-
parator is fixed at 100mV.
The UVLO pin can also be used to implement various re-
mote enable / disable functions. Pulling the UVLO pin below
the 0.4V threshold totally disables the controller. Pulling the
UVLO pin to a potential between 1.25 and 0.4V places the
controller in standby with the VCC and REF regulators op-
erating. Turning off a converter by forcing the UVLO pin to
the standby condition provides a controlled soft-stop. The
controller outputs are not directly disabled in standby mode,
rather the soft-start capacitor is discharged with a 50μA sink
current. Discharging the soft-start capacitor gradually re-
duces the PWM duty cycle to zero, providing a slow con-
trolled discharge of the power converter output filter. This
controlled discharge can help prevent uncontrolled behavior
of self-driven synchronous rectifiers during turn-off.
PWM Outputs
The relative phase of the main switch gate driver OUT_Aand
active clamp gate driver OUT_B can be configured for mul-
tiple applications. For active clamp configurations utilizing a
ground referenced P-Channel clamp switch, the two outputs
should be in phase, with the active clamp output overlapping
the main output. For active clamp configurations utilizing a
high side N-Channel switch, the active clamp output should
be out of phase with main output and there should be a dead
time between the two gate drive pulses. A distinguishing
feature of the LM5026 is the ability to accurately configure
either deadtime (both off) or overlap time (both on) of the
gate driver outputs. The overlap / deadtime magnitude is
controlled by the resistor value (RSET) connected to the
TIME pin of the controller. The opposite end of the resistor
can be connected to either REF for deadtime control or to
AGND for overlap control. The internal configuration detector
senses the direction of current flow in the TIME pin resistor
and configures the phase relationship of the main and active
clamp outputs.
L
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM5026MTX/NOPB 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
LM5026SD 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
LM5026SD/NOPB 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
LM5026SDX 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
LM5026SDX/NOPB 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
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