参数资料
| 型号： | NCP1573DR2 |
| 厂商： | ON Semiconductor |
| 文件页数： | 12/17页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 8-SOIC |
| 产品变化通告： | Product Discontinuation 31/Mar/2005 |
| 标准包装： | 1 |
| PWM 型： | 电流/电压模式，V²? |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 电源电压： | 11.4 V ~ 12.6 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 125°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 剪切带 (CT) |
| 其它名称： | NCP1573DR2OSCT |
NCP1573
IRIPPLE +
(VIN * VOUT)VOUT
(fOSC)(L)(VIN)
Ra for an inductor designed to conduct 20 A to 30 A is
approximately 45 ° C/W. The inductor temperature is given as:
IOUT(MAX) + ISWITCH(MAX) *
(VIN(MIN) * VOUT)VOUT
(fOSC)(ISWITCH(MAX))(VIN(MIN))
Peak inductor current is defined as the load current plus
half of the peak current. Peak current must be less than the
maximum rated FET switch current, and must also be less
than the inductor saturation current. Thus, the maximum
output current can be defined as:
VIN(MAX) * VOUT VOUT
2 fOSC L VIN(MAX)
Since the maximum output current must be less than the
maximum switch current, the minimum inductance required
can be determined.
L(MIN) +
T(inductor) + D T(inductor) ) Tambient
V CC Bypass Filtering
A small RC filter should be added between module V CC
and the V CC input to the IC. A 10 Ω resistor and a 0.47 μ F
capacitor should be sufficient to ensure the controller IC does
not operate erratically due to injected noise, and will also
supply reserve charge for the onboard gate drivers.
Input Filter Capacitors
The input filter capacitors provide a charge reservoir that
minimizes supply voltage variations due to changes in current
flowing through the switch FETs. These capacitors must be
chosen primarily for ripple current rating.
This equation identifies the value of inductor that will
provide the full rated switch current as inductor ripple current,
and will usually result in inefficient system operation. The
system will sink current away from the load during some
portion of the duty cycle unless load current is greater than
V IN
L IN
I IN(AVE)
C IN
L OUT
V OUT
C OUT
half of the rated switch current. Some value larger than the
minimum inductance must be used to ensure the converter
does not sink current. Choosing larger values of inductor will
I RMS(CIN)
CONTROL
INPUT
reduce the ripple current, and inductor value can be designed
to accommodate a particular value of ripple current by
replacing I SWITCH(MAX) with a desired value of I RIPPLE :
Figure 22.
Consider the schematic shown in Figure 22. The average
L(RIPPLE) +
(VIN(MIN) * VOUT)VOUT
(fOSC)(IRIPPLE)(VIN(MIN))
current flowing in the input inductor L IN for any given
output current is:
(L)( D IOUT)
(VIN * VOUT)
(L)( D IOUT)
(VOUT)
IIN(AVE) + IOUT
VRIPPLE + ESRC IRIPPLE +
I 2IN(AVE) ) OUT
VIN
IOUT per phase * IIN(AVE) 2 * I 2IN(AVE)
However, reducing the ripple current will cause transient
response times to increase. The response times for both
increasing and decreasing current steps are shown below.
TRESPONSE(INCREASING) +
TRESPONSE(DECREASING) +
Inductor value selection also depends on how much output
ripple voltage the system can tolerate. Output ripple voltage
is defined as the product of the output ripple current and the
output filter capacitor ESR.
Thus, output ripple voltage can be calculated as:
ESRC VIN * VOUT VOUT
fOSC L VIN
Finally, we should consider power dissipation in the
output inductors. Power dissipation is proportional to the
square of inductor current:
PD + (I 2L )(ESRL)
The temperature rise of the inductor relative to the air
surrounding it is defined as the product of power dissipation
and thermal resistance to ambient:
D T(inductor) + (Ra)(PD)
VOUT
VIN
Input capacitor current is positive into the capacitor when
the switch FETs are off, and negative out of the capacitor
when the switch FETs are on. When the switches are off,
I IN(AVE) flows into the capacitor. When the switches are on,
capacitor current is equal to the per ? phase output current
minus I IN(AVE) . If we ignore the small current variation due
to the output ripple current, we can approximate the input
capacitor current waveform as a square wave. We can then
calculate the RMS input capacitor ripple current:
V
IRMS(CIN) +
The input capacitance must be designed to conduct the
worst case input ripple current. This will require several
capacitors in parallel. In addition to the worst case current,
attention must be paid to the capacitor manufacturer ’s
derating for operation over temperature.
As an example, let us define the input capacitance for a
5 V to 3.3 V conversion at 10 A at an ambient temperature
of 60 ° C. Efficiency of 80% is assumed. Average input
current in the input filter inductor is:
http://onsemi.com
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