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參數(shù)資料
| 型號： | LT3751IUFD#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PQCC20 |
| 封裝： | 4 X 5 MM, LEAD FREE, PLASTIC, QFN-20 |
| 文件頁數(shù)： | 8/34頁 |
| 文件大?。?/td> | 403K |
| 代理商： | LT3751IUFD#TRPBF |
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LT3751
16
3751fb
APPLICATIONS INFORMATION
The total propagation delay, td,isthesecondmostdominant
factor that affects efciency and is the summation of gate
driver on-off propagation delays and the discharge time
associated with the secondary winding capacitance. There
are two effective methods to reduce the total propagation
delay. First, reduce the total capacitance on the secondary
winding, most notably the diode capacitance. Second,
reduce the total required NMOS gate charge. Figure 8
shows the effect of large secondary capacitance.
The energy stored in the secondary winding capacitance
is CSEC VOUT2. This energy is reected to the
primary when the diode stops forward conduction. If the
reected capacitance is greater than the total NMOS drain
capacitance, the drain of the NMOS power switch goes
negative and its intrinsic body diode conducts. It takes
some time for this energy to be dissipated and thus adds
to the total propagation delay.
Choosing Regulator Maximum IPK
The IPK parameter in regulation mode is calculated based
on the desired maximum output power instead of charge
time like that in a capacitor charger application.
I
PK = 2
P
OUT(AVG)
Efficiency
1
V
TRANS
+
N
V
OUT
Note that the LT3751 regulation scheme varies the peak
current based on the output load current. The maximum
IPK is only reached during charge mode or during heavy
load conditions where output power is maximized.
Figure 8. Effect of Secondary Winding Capacitance
VDRAIN
3751 F08
ISEC
IPRI
NO SEC.
CAPACITANCE
SEC. DISCHARGE
t
Transformer Design
The transformer’s primary inductance, LPRI, is determined
by the desired VOUT and previously calculated N and IPK
parameters. Use the following equation to select LPRI:
L
PRI =
3
μs V
OUT
I
PK N
The previous equation guarantees that the VOUTcomparator
has enough time to sense the yback waveform and trip
the DONE pin latch. Operating VOUT signicantly higher
than that used to calculate LPRI could result in a runaway
condition and overcharge the output capacitor.
The LPRI equation is adequate for most regulator
applications. Note that if both IPK and N are increased
signicantly for a given VTRANS and VOUT, the maximum
IPK will not be reached within the refresh clock period. This
will result in a lower than expected maximum output power.
To prevent this from occurring, maintain the condition in
the following equation.
L
PRI <
38
μs
I
PK
1
V
TRANS
+
N
V
OUT
The upper constraint on LPRI can be reduced by increasing
VTRANS and starting the design process over. The best
regulation occurs when operating the boundary-mode
frequency above 100kHz (refer to Operation section for
boundary-mode denition).
Figure 9 denes the maximum boundary-mode switching
frequency when operating at a desired output power level
and is normalized to LPRI/POUT (μH/Watt). The relationship
of output power, boundary-mode frequency, IPK, and
primary inductance can be used as a guide throughout
the design process.
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| LT3754 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:16-Channel 50mA LED |
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| LT3754EUH#TRPBF | 功能描述:IC LED DVR 16CH 50MA 32QFN RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動器 系列:- 標準包裝:6,000 系列:- 恒定電流:- 恒定電壓:- 拓撲:開路漏極，PWM 輸出數(shù):4 內(nèi)部驅(qū)動器:是 類型 - 主要:LED 閃爍器 類型 - 次要:- 頻率:400kHz 電源電壓:2.3 V ~ 5.5 V 輸出電壓:- 安裝類型:表面貼裝 封裝/外殼:8-VFDFN 裸露焊盤 供應商設備封裝:8-HVSON 包裝:帶卷 (TR) 工作溫度:-40°C ~ 85°C 其它名稱:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
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| LT3754EUHTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:16-Channel × 50mA LED Driver |
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