參數(shù)資料
型號(hào): LM3524DMWC
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 穩(wěn)壓器
英文描述: 0.2 A SWITCHING CONTROLLER, 350 kHz SWITCHING FREQ-MAX, UUC
封裝: WAFER
文件頁(yè)數(shù): 7/22頁(yè)
文件大?。?/td> 728K
代理商: LM3524DMWC
Typical Applications (Continued)
In calculating the output capacitor C
o it can be seen that Co
supplies I
o during tON. The voltage change on Co during this
time will be some
V
c = Vo or the output ripple of the regu-
lator. Calculation of C
o is:
where: C
o is in farads, f is the switching frequency,
V
o is the p-p output ripple
Calculation of inductor L1 is as follows:
V
IN is applied across L1
where: L1 is in henrys, f is the switching frequency in Hz
To apply the above theory, a complete step-up switching
regulator is shown in
Figure 20. Since V
IN is 5V, VREF is tied
to V
IN. The input voltage is divided by 2 to bias the error am-
plifier’s inverting input. The output voltage is:
The network D1, C1 forms a slow start circuit.
This holds the output of the error amplifier initially low thus
reducing the duty-cycle to a minimum. Without the slow start
circuit the inductor may saturate at turn-on because it has to
supply high peak currents to charge the output capacitor
from 0V. It should also be noted that this circuit has no sup-
ply rejection. By adding a reference voltage at the
non-inverting input to the error amplifier, see
Figure 21, the
input voltage variations are rejected.
The LM3524D can also be used in inductorless switching
regulators.
Figure 22 shows a polarity inverter which if con-
nected to
Figure 20 provides a 15V unregulated output.
www.national.com
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