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参数资料
| 型号： | 750108 |
| 厂商： | Wurth Electronics Inc |
| 文件页数： | 19/30页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR LT3748 |
| 设计资源： | LT3748 Design Schematic/Tips |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，隔离 |
| 功率 - 输出： | 30W |
| 输出电压： | 12V |
| 电流 - 输出： | 2.5A |
| 输入电压： | 22 ~ 75 V |
| 稳压器拓扑结构： | 回扫 |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | LT3748 |
| 相关产品： | LT3748HMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748HMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP |
| 其它名称： | 732-3308 |
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LT3748
APPLICATIONS INFORMATION
LT3748
V IN
5V TO 100V
3.0
V IN = 5V
2.5
LDO
INTV CC
(V IN – DROPOUT) TO 7V
2.0
1.5
1.0
INTV CC UVLO = 3.6V
I INTVCC = 20mA
LT3748
V IN
5V TO 20V
0.5
LDO
0
–50 –25
0
25
50
75
100 125 150
TEMPERATURE ( C)
3748 F12
INTV CC
OPTIONAL
Figure 12. INTV CC Current at Low V IN Can Cause the LT3748 to
Stop Switching Due to INTV CC Undervoltage Lockout
LT3748
V IN
5V TO 100V
and I INTVCC = 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
LDO
3.6V < BIAS < 20V,
the LT3748 will stop switching.
INTV CC
V IN > BIAS
EXTERNAL SUPPLY
OR THIRD WINDING
Overdriving INTV CC with a Third Winding
3748 F09
Figure 11. INTV CC Pin Configurations
selected MOSFET switch at the expected V IN and INTV CC
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 (N PS ), 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:
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 48V IN ,
10W application, overdriving the INTV CC 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 V C pin. Typical values are in the
f SW(MAX) ≈
L PRI ? I LIM(MIN) ? ( V OUT + V F(DIODE) ? N PS + V IN(MAX)
V IN(MAX) ? ( V OUT + V F(DIODE) ) ? N PS
)
range of R C = 50k and C C = 1nF (see the numerous sche-
matics in the Typical Applications section for other possible
values). If too large of an R C value is used, the part will be
more susceptible to high frequency noise and jitter. If too
With the maximum INTV CC current calculated, the expected
dropout when V IN drops below 7V can be extracted from
the curves in the Typical Performance Characteristics sec-
tion. The LT3748 is tested as low as V IN = 5V but the hard
limit on minimum V IN operation is the INTV CC regulator
dropout and the 3.6V under voltage lockout. Figure 12
illustrates an example where operation with V IN = 5V
small of an R C value is used, the transient performance will
suffer. The value choice for C C is somewhat the inverse
of the R C choice: if too small a C C value is used, the loop
may be unstable and if too large a C C value is used, the
transient performance will also suffer. Transient response
plays an important role for any DC/DC converter.
3748fa
19
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