參數(shù)資料
型號(hào)： LM3151MHX-2.5
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 250 kHz SWITCHING FREQ-MAX, PDSO14
封裝： TSSOP-14
文件頁(yè)數(shù)： 5/20頁(yè)
文件大小： 479K
代理商： LM3151MHX-2.5
4. Determine Output Capacitance
Typical hysteretic COT converters similar to the LM3151/2/3
require a certain amount of ripple that is generated across the
ESR of the output capacitor and fed back to the error com-
parator. Emulated Ripple Mode control built into the
LM3151/2/3 will recreate a similar ripple signal and thus the
requirement for output capacitor ESR will decrease compared
to a typical Hysteretic COT converter. The emulated ripple is
generated by sensing the voltage signal across the low-side
FET and is then compared to the FB voltage at the error com-
parator input to determine when to initiate the next on-time
period.
C
Omin = 70 / (fs
2
x L)
The maximum ESR allowed to prevent over-voltage protec-
tion during normal operation is:
ESR
max = (80 mV x L) / ETmin
ET
min is calculated using VIN-MIN
The minimum ESR must meet both of the following criteria:
ESR
min ≥ (15 mV x L) / ETmax
ESR
min ≥ [ETmax / (VIN - VOUT)]/ CO
ET
max is calculated using VIN-MAX.
Any additional parallel capacitors should be chosen so that
their effective impedance will not negatively attenuate the
output ripple voltage.
5. MOSFET Selection
The high-side and low-side FETs must have a drain to source
(V
DS) rating of at least 1.2 x VIN.
The gate drive current from VCC must not exceed the mini-
mum current limit of VCC. The drive current from VCC can be
calculated with:
I
VCCdrive = Qgtotal x fS
Where, Q
gtotal is the combined total gate charge of the high-
side and low-side FETs.
Use the following equations to calculate the current limit, I
CL,
as shown in Figure 1.
T
j is the junction temperature of the LM3151/2/3.
The plateau voltage of the FET V
GS vs Qg curve, as shown in
Figure 3 must be less than VCC - 750 mV.
30053281
FIGURE 3. Typical MOSFET Gate Charge Curve
See following design example for estimated power dissipation
calculation.
6. Calculate Input Capacitance
The main parameters for the input capacitor are the voltage
rating, which must be greater than or equal to the maximum
DC input voltage of the power supply, and its rms current rat-
ing. The maximum rms current is approximately 50% of the
maximum load current.
Where,
ΔV
IN-MAX is the maximum allowable input ripple volt-
age. A good starting point for the input ripple voltage is 5% of
V
IN.
When using low ESR ceramic capacitors on the input of the
LM3151/2/3 a resonant circuit can be formed with the
impedance of the input power supply and parasitic impedance
of long leads/PCB traces to the LM3151/2/3 input capacitors.
It is recommended to use a damping capacitor under these
circumstances, such as aluminum electrolytic that will prevent
ringing on the input. The damping capacitor should be chosen
to be approximately 5 times greater than the parallel ceramic
capacitors combination. The total input capacitance should
be greater than 10 times the input inductance of the power
supply leads/pcb trace. The damping capacitor should also
be chosen to handle its share of the rms input current which
is shared proportionately with the parallel impedance of the
ceramic capacitors and aluminum electrolytic at the
LM3151/2/3 switching frequency.
The C
BYP capacitor should be placed directly at the VIN pin.
The recommended value is 0.1 F.
7. Calculate Soft-Start Capacitor
Where t
SS is the soft-start time in seconds and Vref = 0.6V.
13
www.national.com
LM3151/LM3152/LM3153
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM3151MHX-3.3 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:SIMPLE SWITCHER? CONTROLLER, High Input Voltage Synchronous Step-Down
LM3151MHX-3.3/NOPB 功能描述:DC/DC 開(kāi)關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
LM3152 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:SIMPLE SWITCHER? CONTROLLER, High Input Voltage Synchronous Step-Down
LM3152-3.3 制造商:Texas Instruments 功能描述:REGULATOR 3.3V VOLTAGE 12A 14TSSOP
LM3152-3.3DEMO 功能描述:電源管理IC開(kāi)發(fā)工具 LM3152-3.3 DEMO BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類(lèi)型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V
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