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参数资料
| 型号： | IRDC3871 |
| 厂商： | International Rectifier |
| 文件页数： | 16/21页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR IRDC3871 |
| 标准包装： | 1 |
| 系列： | SupIRBuck™ |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 1.05V |
| 电流 - 输出： | 8A |
| 输入电压： | 12V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 300kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | IR3871 |
IR3871MPBF
DESIGN EXAMPLE
Design Criteria:
Input Voltage, VIN, = 6V to 21V
Output Voltage, VOUT = 1.25V
Switching Frequency, FS = 400KHz
Inductor Ripple Current, 2ΔI = 3A
Maximum Output Current, IOUT = 6A
Choose an inductor with the lowest DCR and
AC power loss as possible to increase the
overall system efficiency. For instance, choose
an FDU0650-R82M manufactured by TOKO.
The inductance of this part is 820nH and has
4.2 mΩ DCR. Ripple current needs to be
recalculated using the chosen inductor.
Over Current Trip, IOC = 9A
Overshoot Allowance, VOS = VOUT + 50mV
Undershoot Allowance, VDROP = 50mV
ΔI ?
1.25 V ? ? 21 V - 1.25 V ?
2 ? 21 V ? 0.82 ? H ? 400k Hz
? 1.75 A
R FF ?
? 156 k ?
1 ? 1.75 A ?
I IN_RMS ? 6 A ?
? 1 ? ? ?
? ? 1.5 A
Find R FF :
1.25 V
1 V ? 20 pF ? 400k Hz
Pick a standard value 158 kΩ, 1% resistor.
Choose an input capacitor:
1.25V
21 V 3 ? 6 A ?
2
Find R SET :
A
Panasonic
10μF
(ECJ3YB1E106M)
R SET ?
1.4 ? 10m ? ? 9 A
20 ? A
? 6.3 k ?
accommodates 6 Arms of ripple current at
300KHz. Due to the chemistry of multilayer
ceramic capacitors, the capacitance varies over
The R DSON of the lower MOSFET could be
expected to increase by a factor of 1.4 over
temperature. Therefore, pick a 6.49 kΩ, 1%
standard resistor.
Find a resistive voltage divider for V OUT = 1.25V:
temperature and operating voltage, both AC and
DC. One 10μF capacitor is recommended. In a
practical solution, one 1μF capacitor is required
along with 10μF. The purpose of the 1μF
capacitor is to suppress the switching noise and
deliver high frequency current.
V FB ?
R 2
R 2 ? R 1
? V OUT ? 0.5 V
Choose an output capacitor:
To meet the undershoot specification, select a
R 2 = 1.33k Ω , R 1 = 1.96 kΩ, both 1% standard
resistors .
Choose the soft start capacitor:
Once the soft start time has chosen, such as
1000us to reach to the reference voltage, a 22nF
for C SS is used to meet 1000μs.
set of output capacitors which has an equivalent
ESR of 10 mΩ (50mV/5A). To meet the
overshoot specification, equation 8 will be used
to calculate the minimum output capacitance.
As a result, 160μF will be needed for 5A load
remover. Combine those two requirements, one
can choose a set of output capacitors from
manufactures such as SP-Cap (Specialty
V OUT ? ? V IN ? V OUT ?
1.25 V ? ? 21 V - 1.25 V ?
Choose an inductor to
specification:
L ?
V IN ? 2 Δ I ? F s
?
21 V ? 3 A ? 400k Hz
meet
the
design
Polymer Capacitor) from Panasonic or
POSCAP from Sanyo. A 150μF
(EEFSL0D151R) from Panasonic is
recommended. This capacitor has 9 mΩ ESR
which leaves margin for the voltage drop of the
ESL during load step up. The typical ESL for
this capacitor is around 2nH.
? 1.0 ? H
16
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