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| 型号： | LT1533IS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20页 |
| 文件大小： | 0K |
| 描述： | IC REG PUSH-PLL CTRLR ISO 16SOIC |
| 标准包装： | 50 |
| 类型： | 推挽式控制器，隔离式 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.3 V ~ 30 V |
| 输入电压： | 2.7 V ~ 23 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz ~ 250kHz |
| 电流 - 输出： | 1A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 16-SOIC |
| 产品目录页面： | 1327 (CN2011-ZH PDF) |
LT1533
APPLICATIO N S I N FOR M ATIO N
R VC
2k
C VC
0.01 μ F
C VC2
4.7nF
V C PIN
1533 F03
turns ratio of the transformer. The turns ratio must be
large enough to ensure that the transformer can put out a
voltage equal to the output voltage plus the diode under
minimum input conditions.
Figure 3
To prevent irregular switching, V C pin ripple should be
N =
2 ? DC MAX ( V IN ( MIN ) ? V SW
V OUT + V F
)
kept below 50mV P-P . Worst-case V C pin ripple occurs at
maximum output load current and will also be increased if
poor quality (high ESR) output capacitors are used. The
addition of a 0.0047 μ F capacitor on the V C pin reduces
switching frequency ripple to only a few millivolts. A low
value for R VC will also reduce V C pin ripple, but loop phase
margin may be inadequate.
DC MAX is the maximum duty cycle of each driver with
respect to the entire cycle which consists of two periods
(Q1A on and Q1B on). So the effective duty cycle is
2 ? DC MAX . The controller, in general, determines maxi-
mum duty cycle. A 44% maximum duty cycle is a guaran-
teed value for this part.
Some Common Turns Ratios
Magnetics
Design of magnetics is dependent on topology. The fol-
lowing details the design of the magnetics for a push-pull
converter. In this converter the transformer usually stores
V IN
5 ± 10%
5 ± 10%
5 ± 10%
V OUT
12
15
3.3
N
3.6
4.4
1.1
little energy. The following equations should be consid-
ered as the starting point to building a prototype.
Remember to add sufficient margin in the turns ratio to
account for IR drops in the transformer windings, worst-
V IN
T1
1:N
D S1
V SEC
D S2
L O
+
C O
V OUT
case diode forward drop (V F ) and switch-on voltage (V SW ).
There are a number of ways to choose the inductance
value for L O . We suggest as a starting point that L O be
Q1A
selected such that the converter is continuous at
Q1B
1533 F04
I OUT(MAX) /4. If your minimum I OUT is higher than this, or
you are operating at low currents such that the IC and
components can handle higher peak currents, then use a
Figure 4
The following definitions will be used:
V IN = Input supply voltage
V SW = Switch-on voltage
V OUT = Desired output voltage
I OUT = Output current
f = Oscillator frequency
V F = Forward drop of the rectifier
Duty cycle is the major defining equation for this topology.
Note that the output L and C basically filter the chopped
higher number.
Continuous operation occurs when the current in the
inductor never goes to zero. Discontinuous operation
occurs when the inductor current drops to zero before the
start of the next cycle and can occur with small inductors
and light loads. There is nothing inherently bad about
discontinuous operation, however, the converter control
and operation is somewhat different. The inductor is
smaller for discontinuous operation but the peak currents
in the switch, the transformer, the diodes, inductor and
capacitor will be higher. But for low power situations these
may not present a big constraint.
voltage so duty cycle controls output voltage. N is the
11
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