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參數(shù)資料
| 型號： | LT3748HMS#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO12 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-16/12 |
| 文件頁數(shù)： | 11/30頁 |
| 文件大小： | 284K |
| 代理商： | LT3748HMS#PBF |
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LT3748
19
3748fa
APPLICATIONS INFORMATION
selected MOSFET switch at the expected VIN and INTVCC
voltages and multiply that charge required with each
turn-on event by the maximum operating frequency. The
maximum operating frequency in a given application can
be approximated from the primary transformer inductance,
the windings ratio (NPS), the nominal output voltage and
the maximum input voltage. Unless the part is limited by
minimum on- or off-times, this maximum frequency will
occur when the part is regulating in boundary mode at the
minimum peak switch current, and can be derived from:
fSW(MAX) ≈
VIN(MAX) VOUT + VF(DIODE)
() NPS
LPRI ILIM(MIN) VOUT + VF(DIODE) NPS + VIN(MAX)
()
With the maximum INTVCCcurrentcalculated,theexpected
dropout when VIN drops below 7V can be extracted from
the curves in the Typical Performance Characteristics sec-
tion. The LT3748 is tested as low as VIN = 5V but the hard
limit on minimum VIN operation is the INTVCC regulator
dropout and the 3.6V under voltage lockout. Figure 12
illustrates an example where operation with VIN = 5V
and IINTVCC = 20mA might be fully functional at room
temperature, but when the dropout for the same current
exceeds 1.4V and trips the UVLO at higher temperatures
the LT3748 will stop switching.
Overdriving INTVCC with a Third Winding
The LT3748 provides excellent output voltage regulation
without the need for an opto-coupler or third winding,
but for some applications with input voltages greater than
20V, an additional winding may improve overall system
efficiency. The third winding should be designed to out-
put a voltage between 7.2V and 20V. For a typical 48VIN,
10W application, overdriving the INTVCC pin may improve
efficiency by several percent at maximum load and as
much as 30% at light loads.
Loop Compensation
The LT3748 is compensated using an external resistor-
capacitor network on the VC pin. Typical values are in the
range of RC = 50k and CC = 1nF (see the numerous sche-
matics in the Typical Applications section for other possible
values). If too large of an RC value is used, the part will be
more susceptible to high frequency noise and jitter. If too
small of an RC value is used, the transient performance will
suffer. The value choice for CC is somewhat the inverse
of the RC choice: if too small a CC value is used, the loop
may be unstable and if too large a CC value is used, the
transient performance will also suffer. Transient response
plays an important role for any DC/DC converter.
LT3748
3.6V < BIAS < 20V,
VIN > BIAS
5V TO 100V
INTVCC
VIN
3748 F09
EXTERNAL SUPPLY
OR THIRD WINDING
LDO
LT3748
(VIN – DROPOUT) TO 7V
5V TO 100V
INTVCC
VIN
LDO
LT3748
5V TO 20V
INTVCC
VIN
OPTIONAL
LDO
Figure 11. INTVCC Pin Configurations
TEMPERATURE ( C)
–50
0
INTV
CC
DROPOUT
(V)
0.5
1.0
1.5
2.0
050
100
150
3748 F12
2.5
3.0
–25
25
75
125
VIN = 5V
INTVCC UVLO = 3.6V
IINTVCC = 20mA
Figure 12. INTVCC Current at Low VIN Can Cause the LT3748 to
Stop Switching Due to INTVCC Undervoltage Lockout
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| LT3748HMSTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748IMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMSPBF | 制造商:Linear Technology 功能描述:100V Isolated Flyback Controller MSOP16 |
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