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参数资料
| 型号： | IRDC3870 |
| 厂商： | International Rectifier |
| 文件页数： | 13/20页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL REG SUPIRBUCK DC/DC |
| 产品变化通告： | (EP) Parts Discontinuation 25/May/2012 |
| 标准包装： | 1 |
| 系列： | * |
IR3870MPBF
Circuit Description
voltage is within regulation before four
One can use equation 4 to find the required
consecutive soft-start cycles, PGOOD transitions
inductance. The main advantage of small
HIGH to reset the counter.
inductance is increased inductor current slew
rate during a load transient, which leads to a
OVER VOLTAGE PROTECTION
The IR3870 monitors the voltage at the FB node.
If the FB voltage is above the over voltage
threshold, the gates are turned off and the
PGOOD signal is pulled low. Toggling VCC will
allow the next start up.
smaller output capacitance requirement as
discussed in the Output Capacitor Selection
section. The draw back of using smaller
inductances is increased switching power loss in
upper MOSFET, which reduces the system
efficiency and increases the thermal dissipation
as discussed in the Power Loss section.
CHARGE PUMP
The purpose of the charge pump is to improve
the system efficiency. A combination of VCC, V5
and three external components are used to boost
PVCC up to V CPTH . PVCC drives the
synchronous MOSFET and reduces the R DSON
when compared to a regular 5V rail driver. The
lower FET RDSON reduces the conduction
power loss as discussed in the Power Loss
section. The charge pump is continuously
enabled for FCCM = HIGH. The charge pump
circuit is disabled when FCCM = LOW and the
output loading is less than half of inductor current
ripple. In this case, PVCC is two diode voltages
away from the V5 rail. Therefore, the power loss
for driver is reduced. The charge pump circuit
stops switching the CPO pin for PVCC above
V CPTH .
Input Capacitor Selection
The main function of the input capacitor bank is
to provide the input ripple current and fast slew
rate current during the load current step up. The
input capacitor bank must have adequate ripple
current carrying capability to handle the total
RMS current. Figure 16 shows a typical input
current. Equation 5 shows the RMS input current.
The RMS input current contains the DC load
current and the inductor ripple current. As shown
in equation 4, the inductor ripple current is
unrelated to the load current. The maximum
RMS input current occurs at the maximum output
current. The maximum power dissipation in the
input capacitor equals the square of the
maximum RMS input current times the input
capacitor’s total ESR.
COMPONENT SELECTION
Selection of components for the converter is an
iterative process which involves meeting the
specifications and trade-offs between performance
and cost. The following sections will guide one
through the process.
Inductor Selection
Inductor selection involves meeting the steady
state output ripple requirement, minimizing the
Figure 16. Typical Input Current Waveform.
1
? f
? t ? ? dt
I IN_RMS ?
?
1 ? Δ I ?
switching loss of upper MOSFETs, meeting
transient response specifications and minimizing
the output capacitance. The output voltage
includes a DC voltage and a small AC ripple
component due to the low pass filter which has
incomplete attenuation of the switching harmonics.
Neglecting the inductance in series with the output
Ts
2
Ts
0
? I OUT ? D ? 1 ? ? ? ? (5)
3 ? I OUT ?
2
capacitor, the magnitude of the AC voltage ripple is
determined by the total inductor ripple current flow
through the total equivalent series resistance
(ESR) of the output capacitor bank.
The voltage rating of the input capacitor needs to be
greater than the maximum input voltage because of
high frequency ringing at the phase node. The typical
percentage is 25%.
Δ I ?
V OUT
L
? ? 1 ? D ? ? Ts ?
V OUT ? ? V IN ? V OUT ?
V IN ? L ? F s
(4)
13
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| IRDC3895 | 功能描述:电源管理IC开发工具 Design Kit Featuring IR3895M RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| IRDC3897 | 功能描述:电源管理IC开发工具 Design Kit POL IC RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
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