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参数资料
| 型号： | LT1533IS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/20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
It is beyond the scope of this data sheet to get into EMI
fundamentals. AN70 contains much information concern-
ing noise in switching regulators and should be consulted.
them, 2) the oscillator will control the placement of output
frequency harmonics which can aid in specific problems
where you might be trying to avoid a certain frequency
bandwidth that is used for detection elsewhere.
Oscillator Frequency
The oscillator determines the switching frequency and
therefore the fundamental positioning of all harmonics.
The use of good quality external components is important
to ensure oscillator frequency stability. The oscillator is a
sawtooth design. A current defined by external resistor R T
is used to charge and discharge the capacitor C T . The
discharge rate is approximately ten times the charge rate.
By allowing the user to have control over both compo-
nents, trimming of oscillator frequency can be more easily
achieved.
The external capacitance C T is chosen by:
C T(nF) = 2180/[f OSC(kHz) ? R T(k ? ) ]
where f OSC is the desired oscillator frequency in kHz.
For R T equal to 16.9k, this simplifies to:
C T(nF) = 129/f OSC(kHz) ,
e.g., C T = 1.29nF for f OSC = 100kHz
Nominally R T should be 16.9k. Since it sets up current, its
temperature coefficient should be selected to compliment
the capacitor. Ideally, both should have low temperature
coefficients.
When the DUTY pin is high or floating, the outputs will be
turned off during the discharge time of the oscillator. Due
to slew rate control, turning off the outputs does not
produce immediate transitions. Turn-off will require the
current to ramp down and the switch voltage to ramp up.
If the DUTY pin is grounded, then the outputs will turn on
or off starting with the clock discharge.
If the FB pin is below 0.4V the oscillator discharge time will
increase, causing the oscillation frequency to decrease by
approximately 6:1. This feature helps minimize power
dissipation during start-up and short-circuit conditions.
Oscillator frequency is important for noise reduction in
two ways: 1) the lower the oscillator frequency the lower
the harmonics of waveforms are, making it easier to filter
8
Oscillator Sync
If a more precise frequency is desired (e.g., to accurately
place harmonics) the oscillator can be synchronized to an
external clock. Set the RC timing components for an
oscillator frequency 10% lower than the desired sync
frequency.
Drive the SYNC pin with a square wave (with greater than
1.4V amplitude). The rising edge of the sync square wave
will initiate clock discharge. The sync pulse should have a
minimum pulse width of 0.5 μ s.
Be careful in sync’ing to frequencies much different from
the part since the internal oscillator charge slope deter-
mines slope compensation. It would be possible to get into
subharmonic oscillation if the sync doesn’t allow for the
charge cycle of the capacitor to initiate slope compensa-
tion. In general, this will not be a problem until the sync
frequency is greater than 1.5 times the oscillator free-run
frequency.
Slew Rate Setting
Setting the voltage and current slew rates is easy. External
resistors to ground on the R VSL and R CSL pins determine
the slew rates. Determining what slew rate to use is more
difficult. There are several ways to approach the problem.
First, start by putting a 50k resistor pot with a 3.9k series
resistance on each pin. In general, the next step will be to
monitor the noise that you are concerned with. Be careful
with measurement technique (consult AN70). Keep probe
ground leads very short.
Usually it will be desirable to keep the voltage and current
slew resistors approximately the same. There are circum-
stances where a better optimization can be found by
adjusting each separately, but as these values are sepa-
rated further, a loss of independence of control will occur.
Starting from the lowest resistor setting adjust the pots
until the noise level meets your guidelines. Note that
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相关代理商/技术参数 |
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| LT1534 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Ultralow Noise 2A Switching Regulators |
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