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参数资料
| 型号： | R1224N532L-TL |
| 厂商： | RICOH COMPANY LTD |
| 元件分类： | 稳压器 |
| 英文描述： | 0.05 A SWITCHING CONTROLLER, 216 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封装： | SOT-23, 5 PIN |
| 文件页数： | 2/11页 |
| 文件大小： | 153K |
| 代理商： | R1224N532L-TL |
12345
Rev. 0.06
- 10 -
s
OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS
When Lx Tr. is ON:
(Wherein, Ripple Current P-P value is described as IRP, ON resistance of LX Tr. is described as Rp the direct current
of the inductor is described as RL.)
VIN=VOUT+(Rp+RL)
×IOUT+L×IRP/ton Equation 3
When Lx Tr. is OFF:
L
×IRP/toff = VF+VOUT+RL×IOUT Equation 4
Put Equation 4 to Equation 3 and solve for ON duty, ton/(toff+ton)=DON,
DON=(VOUT+VF+RL
×IOUT)/(VIN+VF-Rp×IOUT)Equation 5
Ripple Current is as follows;
IRP=(VIN-VOUT-Rp
×IOUT-RL×IOUT)×DON/f/L …Equation 6
Wherein, peak current that flows through L, Lx Tr., and SD is as follows;
ILmax=IOUT+IRP/2
…Equation 7
Consider ILmax, condition of input and output and select external components.
5
The above explanation is directed to the calculation in an ideal case in continuous mode.
s
External Components
1. Inductor
Select an inductor that peak current does not exceed ILmax. If larger current than allowable current flows, magnetic
saturation occurs and make transform efficiency worse.
When the load current is definite, the smaller value of L, the larger the ripple current.
Provided that the allowable current is large in that case and DC current is small, therefore, for large output current,
efficiency is better than using an inductor with a large value of L and vice versa.
2. Diode
Use a diode with low VF (Schottky type is recommended.) and high switching speed.
Reverse voltage rating should be more than VIN and current rating should be equal or more than ILmax.
3. Capacitors
As for CIN, use a capacitor with low ESR (Equivalent Series Resistance) and a capacity of at least 10
F for stable
operation.
COUT can reduce ripple of Output Voltage, therefore 47
F or more value of tantalum type capacitor is
recommended.
4. Lx Transistor
Pch Power MOSFET is required for this IC.
Its breakdown voltage between gate and source should be a few V higher than Input Voltage.
In the case of Input Voltage is low, to turn on MOSFET completely, to use a MOSFET with low threshold voltage is
effective.
If a large load current is necessary for your application and important, choose a MOSFET with low ON resistance
for good efficiency.
If a small load current is mainly necessary for your application, choose a MOSFET with low gate capacity for good
efficiency.
Maximum continuous drain current of MOSFET should be larger than peak current, ILmax.
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