參數(shù)資料
型號(hào)： LM5045MH
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, PDSO28
封裝： ETSSOP-28
文件頁(yè)數(shù)： 13/28頁(yè)
文件大小： 610K
代理商： LM5045MH
The recommended capacitor value range for C
FF is from
100pF to 1800pF. Referring to Figure 9, it can be seen that
C
FF value must be small enough to be discharged with in the
clock pulse-width which is typically within 50ns. The R
DS(ON)
of the internal discharge FET is 5.5
.
The value of R
FF required can be calculated from
For example, assuming a V
RAMP of 1.5V (a good compromise
of signal range and noise immunity), at VIN
MIN of 36V (oscil-
lator frequency of 400 kHz and C
FF = 470pF results in a value
for R
FF of 125 k.
CURRENT MODE CONTROL USING THE LM5045
The LM5045 can be configured for current mode control by
applying a signal proportional to the primary current to the
RAMP pin. One way to achieve this is shown in Figure 10.
The primary current can be sensed using a current trans-
former or sense resistor, the resulting signal is filtered and
applied to the RAMP pin through a resistor used for slope
compensation. It can be seen that the signal applied to the
RAMP pin consists of the primary current information from the
CS pin plus an additional ramp for slope compensation,
added by the resistor R
SLOPE.
The current sense resistor is selected such that during over
current condition, the voltage across the current sense resis-
tor is above the minimum CS threshold of 728mV.
In general, the amount of slope compensation required to
avoid sub-harmonic oscillation is equal to at least one-half the
down-slope of the output inductor current, transformed to the
primary. To mitigate sub-harmonic oscillation after one
switching period, the slope compensation has to be equal to
one times the down slope of the filter inductor current trans-
posed to primary. This is known as deadbeat control. The
slope compensation resistor required to implement dead-beat
control can be calculated as follows:
Where N
TR is the turns-ratio with respect to the primary. For
example, for a 3.3V output converter with a turns-ratio be-
tween primary and secondary of 9:1, an output filter induc-
tance (L
FILTER) of 800nH and a current sense resistor
(R
SENSE) of 15m, RSLOPE of 1.67k will suffice.
VIN and VCC
The voltage applied to the VIN pin, which may be the same
as the system voltage applied to the power transformer’s pri-
mary (V
PWR), can vary in the range of the 14 to 100V. It is
recommended that the filter shown in Figure 11 be used to
suppress the transients that may occur at the input supply.
This is particularly important when VIN is operated close to
the maximum operating rating of the LM5045. The current into
VIN depends primarily on the LM5045’s operating current, the
switching frequency, and any external loads on the VCC pin,
that typically include the gate capacitances of the power
MOSFETs. In typical applications, an auxiliary transformer
winding is connected through a diode to the VCC pin. This pin
must raise VCC voltage above 8V to shut off the internal start-
up regulator.
After the outputs are enabled and the external VCC supply
voltage has begun supplying power to the IC, the current into
the VIN pin drops below 1mA. VIN should remain at a voltage
equal to or above the VCC voltage to avoid reverse current
through the internal body diode of the internal VCC regulator.
FOR APPLICATIONS WITH > 100V INPUT
For applications where the system input voltage exceeds
100V, VIN can be powered from an external start-up regulator
as shown in Figure12. In this configuration, the VIN and VCC
pins should be connected together. The voltage at the VCC
and VIN pins must be greater than 10V (>Max VCC reference
voltage) yet not exceed 16V. To enable operation the VCC
voltage must be raised above 10V. The voltage at the VCC
pin must not exceed 16V. The voltage source at the right side
of Figure 12 is typically derived from the power stage, and
becomes active once the LM5045’s outputs are active.
30145425
FIGURE 10. Current Mode Configuration
www.national.com
20
LM5045
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM5045MH/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
LM5045MHX 制造商:TI 制造商全稱(chēng):Texas Instruments 功能描述:Full-Bridge PWM Controller with Integrated MOSFET Drivers
LM5045MHX/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
LM5045SQ 制造商:TI 制造商全稱(chēng):Texas Instruments 功能描述:Full-Bridge PWM Controller with Integrated MOSFET Drivers
LM5045SQ/NOPB 功能描述:電流型 PWM 控制器 Full-Bridge PWM Cntrlr 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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