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參數(shù)資料
| 型號： | LTC3803HS6-3#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 330 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封裝： | 1 MM HEIGHT, LEAD FREE, PLASTIC, MO-193, TSOT-23, 6 PIN |
| 文件頁數(shù)： | 3/16頁 |
| 文件大小： | 170K |
| 代理商： | LTC3803HS6-3#PBF |
LTC3803-3
11
38033fd
APPLICATIONS INFORMATION
One potential design pitfall is undersizing the value of
capacitor CVCC. In this case, the normal supply current
drawn by the LTC3803-3 will discharge CVCC too rapidly;
before the third winding drive becomes effective, the VCC
turn-off threshold will be reached. The LTC3803-3 turns
off, and the VCC node begins to charge via RSTART back up
to the VCC turn-on threshold. Depending on the particular
situation, this may result in either several on-off cycles
before proper operation is reached or permanent relaxation
oscillation at the VCC node.
Component selection is as follows:
Resistor RSTART should be made small enough to yield a
worst-case minimum charging current greater than the
maximum rated LTC3803-3 start-up current, to ensure
there is enough current to charge CVCC to the VCC turn-
on threshold. It should be made large enough to yield
a worst-case maximum charging current less than the
minimum rated LTC3803-3 supply current, so that in
operation, most of the LTC3803-3’s supply current is
delivered through the third winding. This results in the
highest possible efciency.
Capacitor CVCC should then be made large enough to avoid
the relaxation oscillation behavior described above. This
is complicated to determine theoretically as it depends on
the particulars of the secondary circuit and load behavior.
Empirical testing is recommended.
The third transformer winding should be designed so that
its output voltage, after accounting for the D2’s forward
voltage drop, exceeds the maximum VCCturn-offthreshold.
Also, the third winding’s nominal output voltage should be
at least 0.5V below the minimum rated VCC clamp voltage
to avoid running up against the LTC3803-3’s VCC shunt
regulator, needlessly wasting power.
VCC SHUNT REGULATOR
In applications including a third transformer winding,
the internal VCC shunt regulator serves to protect the
LTC3803-3 from overvoltage transients as the third wind-
ing is powering up.
In applications where a third transformer winding is
undesirable or unavailable, the shunt regulator allows
the LTC3803-3 to be powered through a single dropping
resistor from VIN to VCC, in conjunction with a bypass
capacitor, CVCC, that closely decouples VCC to GND (see
Figure 3). This simplicity comes at the expense of reduced
efciency due to the static power dissipation in the RVCC
dropping resistor.
The shunt regulator can draw up to 25mA through the
VCC pin to GND to drop enough voltage across RVCC to
regulate VCC to around 9.5V. For applications where VIN
is low enough such that the static power dissipation in
RVCC is acceptable, using the VCC shunt regulator is the
simplest way to power the LTC3803-3.
LTC3803-3
VCC
RVCC
CVCC
38033 F03
VIN
GND
Figure 3. Powering the LTC3803-3 Via the
Internal Shunt Regulator
EXTERNAL PREREGULATOR
The circuit in Figure 4 shows a third way to power the
LTC3803-3. An external series preregulator consisting of
series pass transistor Q1, Zener diode D1, and bias resistor
RB brings VCC to at least 7.6V nominal, well above the VCC
turn-off threshold. Resistor RSTART momentarily charges
the VCC node up to the VCC turn-on threshold, enabling
the LTC3803-3.
LTC3803-3
VCC
RSTART
RB
D1
8.2V
Q1
CVCC
38033 F04
VIN
GND
Figure 4. Powering the LTC3803-3 with an External Preregulator
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| LTC3803HS6-5#TRMPBF | 功能描述:IC REG CTRLR FLYBK PWM TSOT23-6 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) |
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